University of Southampton, 2003

FACULTY OF ARTS

DEPARTMENT OF ARCHAEOLOGY

FIRESHED: THE APPLICATION OF GIS

TECHNIQUES TO HISTORIC MILITARY DATA

by Colin Lacey

A dissertation submitted in partial fulfilment of the

requirements for MSc (Archaeological Computing –

Spatial Technology) by instructional course.

‘…we shall defend our Island, whatever the cost may be,

we shall fight on the beaches,

we shall fight on the landing grounds,

we shall fight in the fields and in the streets,

we shall fight in the hills;

we shall never surrender…’

(Winston Churchill, House of Commons, 4th June 1940)

Acknowledgements

I am indebted to the following for assistance during the preparation of this

study:

Colonel (retired) David Hunt, OBE, CEng, MIEE, for providing much-needed

advice of military doctrine and fieldcraft, for leading field trips in the study area

and for devoting much of his spare time to searching for and providing data.

Mr Graeme Earl (University of Southampton), for assistance with visual basic

scripting and frequent technical queries at all hours of the day.

Dr David Wheatley (University of Southampton), for further technical

assistance, conversion of DEM and assistance with development of the

trajectory modelling system.

Dr Marcos Llobera (University of Southampton), for assistance with DEM

smoothing and trajectory modelling.

Mr Chris Webster (Somerset County Council), for provision of DEM and

photographic data.

I am also extremely grateful to my friends and family, especially Steph, for their continuing support, and for putting up with me throughout the summer of 2003.

Table of Contents Chapter 1: Introduction.........................................................................................1

Background to Military Archaeology...............................................................1 Background to GIS in Archaeology .................................................................4 Background to Anti-Invasion Defences ...........................................................5 Aim of the Study ..............................................................................................8

Chapter 2: Methodology.......................................................................................9 Software............................................................................................................9 Source Data ......................................................................................................9

Digital Elevation Model (DEM)...................................................................9 2002 Air Photos..........................................................................................11 1946 Air Photos..........................................................................................11 OS Landline Data .......................................................................................11 1929 OS Mapping.......................................................................................11 Site Data .....................................................................................................12

Selection of Area ............................................................................................13 Elevation Model Preparation..........................................................................16 Physical Properties of Pillboxes .....................................................................17

Type 24 Pillbox ..........................................................................................19 6-Pounder Anti-Tank Emplacement...........................................................21 Vickers Machine Gun Pillboxes.................................................................23

Visibility Analysis ..........................................................................................25 Viewsheds...................................................................................................27 Cumulative Viewsheds...............................................................................30 Attacks by Airborne Troops .......................................................................31 Artillery Observation Posts ........................................................................36

Fireshed Analysis ...........................................................................................48 Analysis of Anti-Tank Weapons ................................................................49 Analysis of Rifle Fire .................................................................................63 Analysis of the Bren Light Machine Gun...................................................65 Complex Firesheds: Trajectory Modelling.................................................70

Chapter 3: Discussion of Results........................................................................87 Credibility of Results......................................................................................87 General Conclusions – what the system as it stands is capable of .................89 Improvements / Future Directions..................................................................90 Conclusions ....................................................................................................95

Appendix I: Background to the Taunton Stopline..............................................97 Appendix II: Site List .......................................................................................102 Appendix III: Principles of Defence.................................................................106 Appendix IV: German Attack Tactics ..............................................................110 Appendix V: Visual Basic Complex Fireshed Script .......................................112 References: .......................................................................................................126

Table of Figures Figure 1: Planned Stoplines in Britain (C. Webster, Somerset County Council,

based on Dobinson 1996, Wills 1985) .........................................................6

Figure 2: The Taunton Stopline (Hunt Unpublished-a) .......................................7

Figure 3: A pair of buildings, digitised as vectors..............................................10

Figure 4: The same buildings converted to 10m resolution raster .....................10

Figure 5: The same buildings converted to 5m resolution raster .......................10

Figure 6: Digital Elevation Model of the study area ..........................................14

Figure 7: 1929 OS map of the study area, showing the Stopline, pillboxes and other defences.............................................................................................15

Figure 8: View restrictions – Vector above the line, 5m resolution raster below.....................................................................................................................17

Figure 9: A Type 24 Pillbox from the Taunton Stopline....................................19

Figure 10: Section of Type 24 Embrasure (adapted from Chief Engineer - Eastern Command 1940) ............................................................................20

Figure 11: Type 24 Pillbox Plan (Wills 1985:30) ..............................................20

Figure 12: 6pdr emplacement MAT 602 high on the embankment of the old Chard Canal near the aqueduct over Langport Road (Photograph: David Hunt)...........................................................................................................21

Figure 14: 6pdr emplacement MAT 604, side elevation (Wills 1985:23) .........22

Figure 15: Vickers Machine Gun Emplacement plan (Wills 1985:38) ..............23

Figure 16: Vickers Machine Gun Emplacement N17a (David Hunt) ................24

Figure 18: The visibility of a man in a hole (Drawn by L. Willoughby-Ellis)...25

Figure 19: Target heights of anti-personnel fire (adapted from War Office 1942d).........................................................................................................26

Figure 20: Testing for the intervisibility of two cells (Wheatley and Gillings 2002:205)....................................................................................................28

Figure 21: Viewshed Bounding Attributes, ArcGIS 8.3 (Drawn by S. Pillinger)....................................................................................................................29

Figure 22: Making a cumulative viewshed from three separate viewsheds.......30

Figure 23: Viewshed: Attack from the air ..........................................................33

Figure 24: A 25pdr weapon in use (Anon 1942)................................................37

Figure 25: Trajectories of guns, howitzers and mortars (David Hunt)...............37

Figure 26: Extract from Division North Artillery Plan (1940)...........................39

Figure 27: Viewsheds of incorrect and correct locations for Knapp OP............40

Figure 28: Durston OP viewshed .......................................................................41

Figure 29: Knapp OP viewshed..........................................................................42

Figure 30: Crimson Hill OP viewshed ...............................................................43

Figure 31: Viewshed of all OPs..........................................................................45

Figure 32: Dead ground from all OPs ................................................................46

Figure 33: Types of anti-tank ditch (Lowry 1996:89)........................................51

Figure 34: 6pdr Anti-Tank Gun, Royal Armoured Corps Tank Museum, Bovington (adapted from Tank Museum photograph)..............................52

Figure 35: Boys Anti-Tank Rifle (David Hunt) .................................................53

Figure 36: Vulnerable points of German tanks (adapted from VIII Corps Unknown) ...................................................................................................54

Figure 37: Screen-shot of newly-created fireshed, ArcGIS ...............................56

Figure 38: 6pdr anti-tank gun fireshed, Crimson Hill ........................................57

Figure 39: Dead ground, southwest of MAT602................................................58

Figure 40: 6pdr emplacement viewshed, Crimson Hill......................................59

Figure 41: 6pdr and Boys fireshed, Crimson Hill ..............................................61

Figure 42: Anti-tank viewshed, Crimson Hill ....................................................62

Figure 43: SMLE rifle (David Hunt)..................................................................63

Figure 44: Bren LMG (War Office 1942c) ........................................................65

Figure 45: Bren LMG on tripod (War Office 1942c).........................................66

Figure 46: Type 24 view and firesheds ..............................................................67

Figure 47: Vickers MMG (Anon 1942)..............................................................70

Figure 48: Pair of Vickers emplacements (arrowed), Crimson Hill, viewed from the attacking side (David Hunt)..................................................................71

Figure 49: Applications of Fire (War Office 1942d)..........................................75

Figure 50: Comparison between parabola and trajectory...................................77

Figure 51: SMLE trajectory plot ........................................................................78

Figure 52: Original elevation model...................................................................80

Figure 53: Distance raster reclassified into 200yd intervals .............................80

Figure 54: Previous raster reclassified with trajectory height above line of sight....................................................................................................................80

Figure 55: Result of subtracting Figure 54 from Figure 52................................80

Figure 56: Viewshed calculated using Figure 55 as DEM .................................80

Figure 57: Resulting fireshed, displayed on original elevation model ...............80

Figure 58: ‘Footprints’ of trajectories ................................................................82

Figure 59: Right angled triangles reflecting points on a trajectory ....................82

Figure 60: Calculating the angle of sight ...........................................................83

Figure 61: Complex Fireshed of MV1, Crimson Hill ........................................85

Figure 62: Theoretical and actual viewsheds, MV1, top of Crimson Hill, suggesting an enfilade role (green = theoretical arc, red = viewshed) .......86

Figure 63: Pillbox M1b, Wrantage, half excavated, illustrating the level to which it was buried to enhance its camouflage ..........................................92

Figure 64: Pillbox M1a, Wrantage, obscured by trees, indicating its height above the surrounding ground ....................................................................93

Figure 65: Overgrown and forgotten: A pillbox on the Great Western Railway, south of Creech, originally disguised as a signal box (David Hunt) ..........95

Figure 66: View from the top of Crimson Hill north towards Wrantage ...........97

Figure 67: Type 24 pillbox, Buckland, Somerset (Tacchi 2003) .......................98

Figure 69: Concrete anti-tank posts added to a railway embankment, Donyatt, Somerset ...................................................................................................100

Figure 70: Road blocks either side of a canal bridge, Donyatt, Somerset........100

Figure 71: Section of the Taunton Stopline defence plan (Crimson Hill), 1940..................................................................................................................101

Figure 72: Defending a bridge or crossing point (Mace 1996:4) .....................108

Table of Tables Table 1: Attribute Codes of 'View Restrictions' Shapefile.................................16

Table 2: Viewshed bounding attributes, ArcGIS 8.3 .........................................29

Table 3: Anti-Tank Target Heights ....................................................................54

Table 4: Target Heights for SMLE Fire .............................................................64

Table 5: Machine Gun Ranges (War Office 1937:4) .........................................72

Table 6: Trajectory Table for Rifle No 1 Mk 3 SMLE firing SAA .303 MkVII ammunition, with muzzle velocity of 2440ft/sec (War Office 1942d) ......77

1

Chapter 1: Introduction This chapter provides a basic review of the scope and background of the

archaeological study of twentieth-century military sites, outlines the principles

of the use of geographical information systems (GIS) in the discipline and

introduces the concept to anti-invasion defences in Britain. Finally, the aim of

the study is discussed.

Background to Military Archaeology Military archaeology is a global phenomenon that has only begun to be studied

in any great detail since the early 1990s (Schofield 2003:8). All work up to this

point had largely been carried out by amateurs fulfilling their own curiosity. The

end of the Cold War in 1990 brought about a change in the attitudes of the

general public toward military sites. ‘…In parallel with the work of professional

historians there has developed a lively popular interest in the physical remains

of recent warfare which are widely viewed as more immediate, local and

accessible than other machinations of politicians and higher command’

(Dobinson et al. 1997:289). For many, there is a living memory (and a degree of

sentiment) connected to their involvement in the construction and use of such

sites (Dobinson et al. 1997:289, Schofield 2001:21), although particularly for

Second World War sites, this is a dwindling resource (English Heritage 2000).

Archaeology and historical research combined are, therefore, becoming the only

sources of information for the study of military sites worldwide, putting them in

line with more ‘conventional’ forms of archaeology.

The Defence of Britain Project exemplifies this amateur-professional

relationship. This was a project set up by the Council for British Archaeology in

April 1995, which invited members of the public to submit site reports of all

kinds of Britain’s surviving military architecture. The final submission date was

in autumn 2001 and the project has resulted in an online searchable database of

military sites, hosted by the Archaeological Data Service. This provides a record

of approximately 20,000 surviving sites of the hundreds of thousands built

(including some 5,500 surviving pillboxes including many of those in the study

area, all built in the latter half of 1940 (Foot 2003:8).) Defence of Britain

records were also submitted to local Sites and Monuments Records (SMRs) and

2

the National Monument Record (NMR) – an action which has, in itself,

instigated a great deal of interest in the subject (Schofield 2003:5).

Following the completion of the Defence of Britain Project, the Project’s co-

ordinator, William Foot, has been commissioned by English Heritage’s

Monuments Protection Programme to create local studies of anti-invasion

landscapes, using 1940s defence plans from the Public Record Office, Kew, the

physical remains and 1946 aerial photographs to record the most coherent and

legible defence landscapes surviving from the 1940-42 period. This two-year

study, known as the ‘Defence Areas Project’ is being carried out in order to

assess structures for preservation, either individually or in collective local

groups (Foot 2003:9). It does not, however, draw on the SMR ‘Officers’ or

other local sources of information; neither does it exploit any GIS analysis.

Likewise, David Hunt, a retired colonel, is carrying out an in-depth study of the

Taunton stop-line (a highly defended inland ‘frontier’, designed in 1940 to

contain any German invasion of the SW peninsular of England). Despite the

level of examination that has been carried out, Schofield’s framework highlights

the need for study ‘with a view to further understanding defence policy and its

implementation at a local level, and set within the national context’ (in press).

John Schofield (Head of Military and Naval Evaluation Programmes, English

Heritage) identified that ‘a GIS-based work to combine strategic ideals and

military doctrine with reality (through viewshed and field-of-fire analyses)’ was

in need of investigation..” in his forthcoming English Heritage research

framework, ‘Modern Military Matters’ (in press). The present study was carried

out on his personal recommendation to fill the gap left in previous research.

Schofield invited David Hunt to contribute to the forthcoming research

framework and at his suggestion, Hunt was asked to support the writer of this

dissertation with both his knowledge of anti-invasion defences gained through

his in-depth research and his specialist military knowledge and experience. This

includes assignments as a Weapons Technical Staff Officer, formal staff

training at the Royal Military College of Science (Army Staff Course Division

I), The RAF Staff College and the German Armed Forces Command and Staff

College. Support took the form of teach-ins, and observations expressed below

are those of the author unless credited.

3

Military archaeologists face a number of challenges in their work. Defence

works were often constructed with great haste under the threat of an enemy

attack at any time and consequently, the records kept are frequently patchy –

that is to say when the records can be found – the British armed forces are not

known for keeping classified documentation until long after its useful life has

ended. Premature destruction of records is also a common occurrence. Although

there is still a surviving element of those that remember World War II first-

hand, those that remember the particular object of the archaeologist’s studies are

frequently difficult to find. Also, the factor that many people, particularly those

with bad experiences of the War, whilst having useful memories, are more

inclined to believe that they are best forgotten. This attitude also percolated

through local and national government and led to the large-scale removal of

World War II archaeology as soon as its use had passed. Despite this, there is

still a great deal to be learned from these relics of one of the tensest periods of

Britain’s recent history. In 1944, once the Allied forces had established

themselves on the Continent, permission was given to start removing anti-

invasion defences across the UK (Hunt 2003).

Challenges particular to the study of anti-invasion defences are also common.

Few senior officers with experience of, and responsibility for the construction

works survive. Few records of their ‘appreciations of the situation’ and reasons

or justifications for decisions taken exist. Anti invasion was a completely new

situation for the Army with new roles to fulfil and considerable overstretching

of resources. The totally unexpected situation post-Dunkirk left the country with

no preparation or contingency plans against a new threat. Britain as an island

nation did not have the history or experiences of a land-based frontier with

permanent fortifications, in contradiction with those of Belgium, France and the

Netherlands. All work was carried out under constant threat of invasion forcing

short cuts to be taken or non- optimal solutions adopted to ensure that, if the

invasion happened, there would be some fortifications for the defenders.

Mistakes were made and documentation was often not produced. Some

fortifications, removed at the end of the war and after, cannot now be surveyed

to establish orientations, fields of view and fields of fire. (Hunt Unpublished-a).

4

Background to GIS in Archaeology GIS … are computer systems whose main purpose is to store, manipulate,

analyse and present information about geographic space.

(Wheatley and Gillings 2002:9)

From the 1970s, heralding the early days of GIS in archaeology (Wheatley and

Gillings 2002:18), there have been many great developments in technology,

both hardware and software based. Modern GIS, with their easy-to-use

graphical user interfaces, and pre-coded macros, used to automate both

frequently-used and complex features and carry out far more than is possible

with a paper map alone. Currently, archaeologists use GIS in many ways.

Simple uses include spatial databases – the foundation for all systems, but often

used alone, in their own right, as three-dimensional data storage media, able to

store, and most importantly, display, the locations as well as the attributes of a

feature. One main use of GIS in archaeology is to take this a step further and ask

why these features are located where they are. Analysis of factors ‘outside the

artefactual sphere’ (Wheatley and Gillings 2002:17) – geology, political

boundaries and effects of natural phenomena such as sunlight and rainfall all

affect the location of, for example, settlement sites, and all can all be modelled

using GIS. A step further still is into the realm of spatial patterning. The use of

GIS to determine whether archaeological site location is random or organised,

based on natural or cultural phenomena, is a common field of study (see for

example Hodder and Orton 1976) This leads into fields such as cost-surface

analysis (e.g. Bell and Lock 2000) and predictive modelling of site location –

using characteristics of known sites to predict the locations of those currently

unknown (see Warren 1990). Increasingly in recent years GIS has become

accepted as an essential tool to Cultural Resource Management as a way to store

and analyse details of significant sites on a regional basis (Wheatley and

Gillings 2002:19).

The archaeological use of GIS exploited in this study is visibility analysis – the

ability of a point to ‘see’ other points. This is explained in greater detail below.

5

Background to Anti-Invasion Defences After the German conquest of France in June 1940 Britain

was alone and in imminent danger of German invasion.

(Alexander 1998)

Immediately following the withdrawal of the British army from Dunkirk in late

May 1940, Britain was the closest it had been to being invaded for centuries.

Since the previous conflicts in the nineteenth century, technology had advanced

to such an extent that Britain’s once formidable coastal defences were now

inadequate against the advanced, highly mobile weaponry of the twentieth

century. The development of the aeroplane, faster ships and the most feared of

new weapons, the tank, meant the risk to the country was dramatically

increased. Immediately the withdrawal from Dunkirk was complete, on

approximately June 4th (Green and Plant 2003), General Sir Edmund Ironside,

Commander in Chief of Home Forces, gave the order for the most intense

period of military construction in England for centuries, and the construction of

‘the largest system of defensive earthworks ever built in England’ (Foot

2003:9).

The concept was simple – to create defended lines, or ‘stoplines’ across the

country that would ‘block the progress of armoured columns, setting them up

for a counter-attack… A stopline would [be] a continuous anti-tank obstacle,

natural if possible, covered by pillboxes and other prepared positions’ (Green

and Plant 2003). ‘Soldiers recently returned from France laboured alongside

civilian workers to build concrete gun-posts and pillboxes for the nations few

remaining weapons’ (Alexander 1998:9).

The immediate object is to divide England into several small

fields surrounded by a hedge of anti-tank obstacles which is

strong defensively, using natural accidents of the ground where

possible. Should Armoured Fighting Vehicles or airborne attacks

break into the enclosures the policy will be to close the gate by

blocking the crossing over the obstacles and to let the ‘dogs’ in

the shape of armoured formations, or other troops, in to round

up the cattle.

(Southern Command 1940)

6

Britain’s main stopline was constructed, running from the west coast of England

to the east, below London, then turning north and stretching to Edinburgh and

beyond. This line was known as the General Headquarters Anti-Tank Line

(GHQ Line) and consisted of a continuous stretch of natural features, anti-tank

obstacles, roadblocks and bridges prepared for demolition should the need arise.

The line was punctuated with pillboxes and gun emplacements – ‘hardened

defence works’ (Foot 2003:8) – of varying sorts, which, using the limited

weaponry available in the aftermath of Dunkirk, were intended to destroy the

attacking force as they became stuck at the anti-tank obstacles. Field artillery

and even anti-aircraft units, which were mobile and had no permanent structures

built for their use, would support pillboxes. Several more stoplines were

constructed in areas to the south and west of the GHQ line, in order that an

attacking army would have to break through several lines before being able to

take control of the country.

Figure 1: Planned Stoplines in Britain (C. Webster, Somerset County Council, based on Dobinson 1996, Wills 1985)

7

‘In principle the General Headquarters Line bore the

unmistakable stamp of linear and frontal defensive lines

established in France during World War One. Unfortunately

many of the weapons available to defend the fortifications of the

General Headquarters Line including ex naval guns, machine-

guns and rifles also dated from the same period.’

(Alexander 1998:9-10)

The Taunton Stopline was a World War II anti-invasion stop line, facing west,

built between July and November 1940. Its aim was to ‘stop an enemy’s

advance from the West and in particular a rapid advance supported by

Armoured Fighting Vehicles (up to the size of a German medium tank) which

may have broken through the forward defences’ (War Office 1940).

Figure 2: The Taunton Stopline (Hunt Unpublished-a)

For a more detailed description of the Taunton Stopline, see Appendix I.

The fronts are everywhere. The trenches are dug in the towns

and streets. Every village is fortified. Every road is barred.

(Winston Churchill, BBC Broadcast, 14th July 1940)

8

Aim of the Study To investigate how GIS-based terrain analysis can contribute to the study

military defences in Britain by using as an example World War II anti-invasion

defences on a selected section of the Taunton Stop Line in South-west England.

Nothing of this kind has previously been carried out for this period of Britain’s

history and it is thought that these important sites from our recent past should be

given the same consideration as is currently being given to more ancient sites. It

should also be noted that the majority of the techniques developed during this

study are also applicable to the archaeological study of weaponry and defences

of all ages – from the Roman fort, ballista and bow-and-arrow, to the motte-and-

bailey castle or classical fortifications such as vauban, the trebuchet and the

cannon, the main differences lie in the scale and weapon properties.

9

Chapter 2: Methodology This section explains the technical aspects of the study, beginning with the

specifications of the software and source data used. The selection criteria for the

area of study are described, as is the procedure of re-working the terrain model

to include features that obstruct the view of an observer. The next section

describes how the physical properties of the types of pillboxes found in the

study area affect their fields of view and fire. Visibility analysis is next covered,

with sections covering observation of attacking parachute troops and the

determination of artillery observation points from somewhat ambiguous

documented locations. Following on, ‘fireshed’ – the devised system of

analysing fields-of-fire of the various weapons on the Stopline – is described in

two forms – flat and curved trajectory weaponry. Each weapon is introduced,

after which the procedures for calculating its fireshed are described, along with

analyses of sample results.

Software The majority of work was carried out using ESRI ArcGIS 8.3 (hereon in

referred to as ArcGIS). Image format transformation was carried out using Corel

Photopaint 11.

Source Data Source data for the project consisted of ESRI shapefiles, raster images, ESRI

grid datasets, and Microsoft Excel spreadsheets. Below, the source data and its

particulars are listed:

Digital Elevation Model (DEM) Description: Raster digital elevation model (DEM) of the county of Somerset.

Point data in 10m grid, Z values obtained from photogrammetry.

Origin: Purchased by Somerset County Council from a third party air-

photo and photogrammetry company.

Processing: Data was compiled from a point text file using ArcGIS, in which,

data for the study area was cropped from the rest of the county.

The resulting data was smoothed using a 6x6 mean filter, due to

regular microtopographical anomalies giving a regular tartan-like

pattern to viewsheds. Finally, the data was resampled from 10m

10

resolution to 5m in order that digitised buildings and hedgerows

measuring less than 10m across were displayed correctly (see

below).

Uses: The DEM was used as a terrain model for viewshed and fireshed

calculation. Photogrammetry data is now considered a ‘viable

alternative to the use of map-based elevation data’ (Wheatley and

Gillings 2002:113).

Figure 3: A pair of buildings, digitised as vectors.

Figure 4: The same buildings converted to 10m resolution raster

(raster = green, vector = blue)

Figure 5: The same buildings converted to 5m resolution raster

(raster = purple, vector = blue)

11

2002 Air Photos Description: 0.25m resolution colour raster images of the study area in

ERMapper ECW format.

Origin: Purchased by Somerset County Council from a third party air-

photo and photogrammetry company.

Processing: None

Uses: Establishment of accurate locations of pillboxes (where still

extant) and ease of navigation and visualisation of the landscape.

1946 Air Photos Description: Incomplete 0.25m resolution monochrome raster images of the

study area in ERMapper ECW format.

Origin: Somerset County Council. Originally taken as reconnaissance

photographs by the Royal Air Force soon after the end of the Second World

War.

Processing: None

Uses: Establishment of accurate locations of pillboxes (where visible –

camouflage was still in good condition in many cases) and ease

of navigation and visualisation of the landscape. There were

many gaps in the 1946 coverage (often in important areas).

OS Landline Data Description: Fully feature-coded vector data of Ordnance Survey 1:2500 scale

mapping.

Origin: Ordnance Survey

Processing: Cropped to study area and converted to shapefiles using ArcGIS.

Uses: Establishment of accurate locations and orientations of pillboxes

(where still extant) and ease of navigation and visualisation of

the landscape.

1929 OS Mapping Description: 0.21m resolution raster data of 1929 Ordnance Survey mapping.

12

Origin: Somerset County Council digital data and University of

Southampton Cartographic Unit map archive sheet maps.

Processing: Digital data was in georeferenced Tagged Image Format (TIF)

and it was decided that, to reduce image size, the images would

be converted to Portable Network Graphic format (PNG) and TIF

world files (TFW) were renamed as PNG world files (PGW) to

preserve georeferencing. Paper maps were scanned using an A4

flatbed scanner, again into PNG format, then georeferenced and

georectified using standard tools in ArcGIS.

Uses: Ease of navigation and visualisation of the landscape prior to the

construction of the Taunton Stopline.

Site Data Description: Details of pillboxes, gun emplacements and crossing points

(SMR number where applicable, grid reference, site description,

designation and site type, bearings where applicable) stored in a

Microsoft Excel spreadsheet.

Origin: Pillbox data from Somerset County Council Sites and

Monuments Record (SMR), crossing points selected from OS

maps as points at which tanks and troops could cross canals,

railways and other physical boundaries forming part of the

stopline (i.e. bridges), compiled by David Hunt as part of his

research into the stopline. Bearings for some sites taken in the

field using magnetic compasses and from air photos / OS

Landline maps

Processing: Excel files converted to shapefiles using ArcToolbox, a facility

of ArcGIS.

Uses: Pillboxes and gun emplacements used as sources for viewsheds

and firesheds, and crossing points used as targets for gunfire, as

the enemy would be ‘funnelled’ into a confined space at these

points.

13

Selection of Area In order to test viewshed and fireshed techniques, a sample area of the Taunton

Stopline was required. An area measuring 6km (E-W) x 8km (N-S) was chosen

on the basis that:

• It featured each of the three main types of pillbox (and therefore all of

the main types of weapons) used on the Stopline.

• There is a high survival rate of pillboxes and accurate locations are

available for those removed.

• Its terrain is highly varied, ranging from 4m to 110m (heights above sea

level), also containing canals and railway cuttings, woodland and

buildings, and consequently is better suited for demonstrating the effect

of terrain on view and fire than a flat piece of ground. Particularly

interesting is Crimson Hill, a large plateau in the southeast corner of the

study area with a steep wooded scarp face dropping from it to the north.

This features several pillboxes aimed out across the steep wooded

hillside.

• Full DEM, 1929 map and 2001 air photo cover, and good 1946 air photo

cover is available in a georeferenced digital format from Somerset

County Council.

• The landscape has changed relatively little since the Second World War.

14

Figure 6: Digital Elevation Model of the study area

15

Figure 7: 1929 OS map of the study area, showing the Stopline, pillboxes and other defences

16

Elevation Model Preparation The digital elevation model of the area had been ‘cleaned’ when produced: Due

to the nature of air photos depicting everything visible at ground level, the DEM

would have initially recorded woodland, hedges, buildings and other articles

standing above ground level as ground level. These features were removed

before the model was supplied to customers. Unfortunately, visibility and field-

of-fire analysis requires that these ‘artefacts’ are present. In order to get around

this problem, woodland, thick hedgerows and some buildings were digitised as

polygons in a shapefile, using the editing tools of ArcGIS. Locations for the

above were obtained largely from 1946 air photos, although for gaps in this

coverage, estimates were derived from a combination of both 1929 OS maps

and 2001 air photos. The attributes of each polygon were coded as to the type of

view restriction they represent using the following table: 1

Code Description Height (m) 1 Woodland 30 2 Thick Hedgerow 1.7 3 Building 10 4 Possible Woodland 30 5 Possible Hedgerow 1.7 6 Possible Building 10 7 Crimson Hill Scrub 1

Table 1: Attribute Codes of 'View Restrictions' Shapefile

Finally, the shapefile was converted (using ArcGIS Spatial Analyst conversion

routine) into a 5m resolution raster dataset containing the height values. This

was added to the elevation model using the ArcGIS Raster Calculator, with the

resulting raster becoming the basis for all future calculations.

This method was chosen above digitising features directly as rasters, due to its

flexibility – it is possible to manipulate polygons and change their values far

more and with less effort than when working with rasters alone.

1 Heights of hedges, scrub and buildings were estimated from modern examples. Modern tree heights were measured using basic trigonometry and averaged giving the approximate height of 30m.

17

Figure 8: View restrictions – Vector above the line, 5m resolution raster below.

Physical Properties of Pillboxes Essentially, a pillbox is a reinforced building in which troops can shelter from

incoming fire and retaliate with their own weapons. Described as ‘probably the

most familiar type of 20th century defensive building’ (Lowry 1996:79), these

structures provided the backbone of defence along the Taunton Stopline. They

were situated both to directly defend vital crossing points and to deter attacking

armies from their task. Designs were issued by branch FW3 of the War Office

Directorate of Fortifications and Works in June 1940 for around twelve types of

pillbox, which were loosely adhered to by regional construction workers (Lowry

1996:79). Three main types of pillbox can be found on the Taunton Stopline.

The most common is the Type 24 thick-walled (shell-proof2) hexagonal pillbox

(also the most common in Britain (Foot 2003:8)). Second is the Vickers

machine gun emplacement and third, the six-pounder anti-tank gun

emplacement – a design specific to the Taunton Stopline. Each pillbox is

characterised by its role, usually governed by the weapon it is designed to hold.

2 The 1936 Army Manual of Field Engineering stated that 3’6” (1.67m) of reinforced concrete would resist a 6” (15.2cm) shell (Alexander 1998:88).

18

This also dictates the shape and size of its loophole or loopholes3 which were

wherever possible, ‘sited to provide interlocking fields of fire with other

pillboxes over the anticipated directions of attack, and designed to minimise

external dimensions, so limiting access to incoming fire, whilst maximising

freedom of movement internally for the weapon and its operator’ (Lowry

1996:79). Another factor of the loophole was that it restricted the vision of those

inside the pillbox, both vertically and horizontally. It is this factor that is

important for the analysis of fields of view and fire.

3 Loopholes – firing loops, embrasures – splayed horizontal slits for looking or firing through (Lowry 1996:79).

19

Type 24 Pillbox

Figure 9: A Type 24 Pillbox from the Taunton Stopline

The type 24, also referred to as an ‘FW3 / Type 24’, is a hexagonal pillbox with

five large loopholes suitable for Bren light machine guns and Boys anti-tank

rifles, each with a ‘table’ formed from the thickness of the wall, on which the

bipod of the weapon would stand. The fifth wall, slightly longer than the others,

featured a central doorway flanked by a single rifle loophole on each side. These

were somewhat cruder in form than the other loopholes and did not have the

luxury of a table for tripod-mounted guns. Tables as such were only provided in

Vickers emplacements, whereas Type 24 boxes had slots built under the

loophole to accommodate the front leg of the tripod of a Bren Light Machine

Gun or a Boys Anti-Tank Rifle. The doorway was situated to the ‘safe’ side of

the stopline (see Figure 9 above) and the rifle loopholes were intended for local

defence only. Internally, the posts featured a ‘Y’ shaped baffle wall to contain

ricochets and blast from incoming fire.

20

Figure 10: Section of Type 24 Embrasure (adapted from Chief Engineer - Eastern Command 1940)

Each main loophole had an arc of fire of approximately 60°, meaning that

allowing for the small gaps between the rifle and main loopholes, type 24

pillboxes could cover almost 360°, and the non-covered area (‘dead ground’)

was entirely behind the stopline, so not of great concern. Vertical restrictions of

view were calculated using the original construction plans (Chief Engineer -

Eastern Command 1940) taking the vertical centre of the loophole as the

observer height. Details of the measurement can be seen in Figure 10 above.

Figure 11: Type 24 Pillbox Plan (Wills 1985:30)

6-Pounder Anti-Tank Emplacement

Figure 12: 6pdr emplacement MAT 602 high on the embankment of the old Chard Canal near the aqueduct over Langport Road (Photograph: David Hunt)

These emplacements were originally open concrete-walled pits as described by

Alexander (1998:92), although at a later date, rear walls (on the ‘safe’ side of

the stopline) and roofs were added to give the gun crew a greater level of

protection from shelling and dive

bombers. The gun was situated on a

pedestal forward of the wall and

could swing through a 180° arc,

which was also the field of vision of

the personnel. It is assumed that

there are no practical restrictions on

elevating the gun to fire up to its

designated range of 600yds or

depressing the gun to engage targets

within its arc of fire (Hunt 2003).

Vertical restrictions on view, dictated

by the presence of the front wall and

Figure 13: Pedestal in MAT 602

(David Hunt)

21

22

roof (see Figure 12 above and Figure 14 below), are considered minimal as the

gun crew are able to move to the front of the emplacement and look upwards

past the roof and downwards past the wall.

Figure 14: 6pdr emplacement MAT 604, side elevation (Wills 1985:23)

23

Vickers Machine Gun Pillboxes

Figure 15: Vickers Machine Gun Emplacement plan (Wills 1985:38)

These pillboxes were characterised by their square shape and a single large

embrasure with a large concrete table inside, where a Vickers machine gun

would stand on its tripod. The boxes also featured two rifle loopholes for local

defence, situated in the walls opposite and to the left of the main embrasure

(when viewed from outside, facing the main embrasure), and in the wall to the

right, a doorway shielded by a separate large concrete blast wall. It should be

noted that pillbox NV15 is unique in that it has two large embrasures, on

adjacent walls. Only one table is present, and it is thought that the embrasure

24

with the table would be used in preference to the other. In all calculations,

therefore, the additional embrasure is analysed separately.

Figure 16: Vickers Machine Gun Emplacement N17a (David Hunt)

Again, the embrasure restricts the view and fire from inside as follows:

As with the Type 24 pillbox above, the rifle loopholes

placed to defend the stopline but are for local defenc

have been ignored in view and field-of-fire calculations

Figure 17: Restrictionsimposed by VickersEmplacement embrasure(adapted from Wills1985:38)

are not a strategic feature

e only. Due to this, they

.

25

Visibility Analysis Reconnaissance is as important in the defence as in the attack.

Active patrolling should be carried out, and the enemy kept

under constant observation by forward infantry posts and

intelligence sections. By the piecing together of small items of

information which in themselves may appear unimportant, the

enemy’s intentions may often be deduced.’

(War Office 1937:145)

The key to the defence and attack of an area is visibility. Opposing sides both

want to see as much of their adversaries as possible, without being seen

themselves. Due to this factor, the terrain can be both an ally and an enemy to

the soldier. It can provide elevated observation points and areas to hide where

the landform masks the view from the observer. These areas in which observers

cannot see their enemy, are known as ‘dead ground’. The level of dead ground

decreases the higher above ground level the subject of observation stands. For

instance, a man crouching in a one meter deep hole may be invisible to the

observer, although when the same man, measuring for instance, 1.6m, stands in

the same hole, the upper 0.6m of his body is visible.

Figure 18: The visibility of a man in a hole (Drawn by L. Willoughby-Ellis)

(green = invisible, red = visible)

26

The technology of warfare in the 1940s meant that there were several levels of

observation desired by the defending force. Observation to ground level – if

anything is present, at any height, it will be seen. Observation to approximately

one metre – the height of a man kneeling or crawling / running whilst bent

double, and the height of the top of the tracks of a tank, meaning the entire hull

of the vehicle is visible. Observation to 1.6m – the height of a standing man and

the turret of a tank (known as ‘hull down’ – i.e. the turret is the only part

visible). Observation to two metres – the top of the turret of a tank – if

approaching over the brow of a hill, the tank commander would raise a flap in

the turret and examine the view over the hill. Alternatively, periscopes would be

used, protruding from the turret This is known as ‘turret down’. Finally,

observation to 91m (300 feet) – incoming parachute troops and dive-bombers.

Figure 19: Target heights of anti-personnel fire (adapted from War Office 1942d)

Even when out of range of weaponry, those defending need a view of the enemy

as soon as possible, in order to get some idea on the direction of forthcoming

attack, and to plan the counter-attack wisely. Moreover it is vital that all

positions along the forward defended localities maintain all-round observation

to gather intelligence and to avoid being surprised by the enemy.

Two main scenarios illustrate this concept and are outlined below: attack by

parachute and artillery observation. The former is a theoretical scenario,

applicable to other defences, but outlined here in principle, and the latter uses

methods described to calculate the likely location of points referenced poorly in

contemporary documents. The military have been estimating fields of view for

many years, by use of the map contours or by drawing cross sections or profiles

of the terrain using physical pen-and-paper methods using contours from maps

as source data (Hunt 2003, War Office 1937:110-11).

27

An attacker would be looking for:

i. Covered approaches, Close or wooded country will offer

special opportunities for a concealed advance and for

outflanking or surprising the enemy.

ii. Positions from which observed covering fire can be brought

to bear.

iii. Features which when occupied or captured will enable to

enemy’s position to be enfiladed and a flank attack to be

made under favourable conditions.

iv. Ground favourable for the co-operation of armoured fighting

vehicles.

v. Probable lines of advance of hostile tanks and the areas in

which hostile tank counter-attacks are likely to be made.

vi. A line of attack by which the advancing troops will be

defiladed as far as possible from enemy weapons.

vii. Facilities for concealment from hostile aircraft.

(War Office 1937:111)

Manual calculation of fields of view and fire is a laborious and time-consuming

exercise that, with good quality GIS software, and a fairly powerful computer,

can be automated into a procedure that takes seconds.

Viewsheds Both scenarios above can be modelled using a common application of GIS in

archaeology – visibility analysis. For many years, the technique of analysing

points that can be seen from other points (viewshed analysis) is widely used in

the planning and civil engineering industries and widely in the modern military

(Fisher, P 1991:1321). Visibility analysis is also by no means a recent

development in archaeology. Well before the advent of GIS, antiquarians, and

later, archaeologists were making basic observations about spatial patterning

and site location (Wheatley and Gillings 2000:1). Further applications were

initially developed in the 1970s, documented by Hodder and Orton (1976) and

Renfrew, in his 1979 report containing analysis of the visibility and

28

intervisibility of prehistoric sites on Orkney. The GIS-based study of visibility

escalated considerably in the 1990s with the development of viewshed analysis

(Wheatley and Gillings 2002:201). Traditionally, viewshed analysis has been

largely restricted to the study of prehistoric archaeology, and it is not thought

that it has been used (in an archaeological sense) on anything as recent as World

War II, although it is at least as useful to this relatively modern period as it is to

the neolithic.

Viewshed calculations in this study use the digital elevation model as prepared

above, and a list of points, as source data. The points represent the observer

points and are automatically assigned an elevation value corresponding to that

of the underlying pixel of the DEM. The calculation that produces the viewshed

is best described by Wheatley and Gillings as follows: ‘…for each cell in the

raster, a straight line be interpolated between the source point and every other

cell within the elevation model. The heights of all the cells which occur on the

straight line between the source and target cells can then be obtained in order to

ascertain whether or not the cell exceeds the height of the three dimensional line

at that point’ (2002:205).

Figure 20: Testing for the intervisibility of two cells (Wheatley and Gillings 2002:205)

Upper example – cell is visible. Lower example – cell is invisible.

The result is a raster dataset in which pixels are coded with the following values

– 0 for invisible from observer point (or in this case, ‘dead ground’) and 1 for

visible. ArcGIS allows the constraining of viewsheds in several ways. Angles

29

and heights can be added as fields to the attribute table for each entry in the

observer point dataset and are as follows:

Attribute Name Description Default Value SPOT Assigns absolute elevation to observer

point (overwriting DEM value) No default

OFFSETA Vertical distance to be added to DEM value at observer point

0

OFFSETB Vertical distance to be added to DEM value at target point

0

AZIMUTH1 Anticlockwise horizontal angle limit of viewshed calculation

0

AZIMUTH2 Clockwise horizontal angle limit of viewshed calculation

360

VERT1 Upper vertical angle limit of viewshed calculation, measured from the horizontal

90

VERT2 Lower vertical angle limit of viewshed calculation, measured from the horizontal

-90

RADIUS1 Inner radius of viewshed area – calculations only occur beyond this distance

0

RADIUS2 Outer radius of viewshed area – calculations do not occur beyond this distance

Infinity

Table 2: Viewshed bounding attributes, ArcGIS 8.3

Figure 21: Viewshed Bounding Attributes, ArcGIS 8.3 (Drawn by S. Pillinger)

30

Cumulative Viewsheds Cumulative viewsheds are a simple sum total of individual viewsheds,

calculated on a pixel-by-pixel basis:

1 0 1 1 0 0 2 1 0 1

+ 0 1

+ 0 1

= 0 3

Figure 22: Making a cumulative viewshed from three separate viewsheds

The resulting raster contains a value per pixel that relates to the number of observer points able to see that pixel. ArcGIS calculates cumulative viewsheds automatically without calculating the individual viewsheds.

31

Attacks by Airborne Troops ‘Parachute troops were dropped from about 300 feet from

aircraft and gliders… Their morale was very low unless

they had time to organise after landing. When attacked at

once they were easily disposed of… Small arms fire against

descending parachute troops was only effective at short

range. The lessons for the Home Guard [and other

defending soldier] in this include:-

(a) Parachute troops must be attacked at the earliest

opportunity. Every second counts in making your plan

and carrying it out. Every moment lost will cost you

lives and ammunition. Risks must be freely taken in

order to gain time. The enemy must be sought out and

destroyed.

(b) You must not wait for parachute troops to attack you.

(c) Memorise covered approaches to all points in your

area where they may land.

(d) If possible prevent them from reaching their arms

containers; the weapons they carry on them are only

short range, so you can snipe them while you are out of

their range…’

(Langdon-Davies, on the German invasion of Crete, and

how it applies to the defence of Britain (1942))

This section uses viewshed analysis to evaluate how the physical constraints of

pillboxes affect the areas in which incoming airborne assaults can be seen at a

height of 300’ (91m).

It can be seen from the training advice given above that the impetus was on

elimination of attacking forces immediately (or prior to) the moment at which

their feet touch the ground. This relies on the knowledge that troops are being

dropped by parachute, which stems from the defending force seeing the

parachutists whilst airborne, or the aircraft from which they are to be dropped.

32

Equally, gliders should be seen on their landing approach glide. As the Vickers

machine gun was primarily an anti-personnel weapon, and due to the

complication of range finding on targets that are not at ground level, together

with the unsuitability of the tripod mounting and sights to track fast moving

aerial targets, making it unlikely that the gun would have been used in such a

way (War Office 1942a makes no reference to attacking aircraft with the

Vickers Machine Gun), it is feasible that it would have been used against just-

landed paratroopers or gliders.

The ability to see such troops or gliders as they descended would be crucial to

the process of aiming and setting the range of the gun on the landing ground to

engage the enemy with fire. Likewise, the ability to descend out of view of the

waiting guns could be a significant benefit to the attacking force. It should be

noted, however, that there is no evidence to suggest that the Taunton Stopline

design was influenced by such factors (Hunt 2003). Nevertheless, the study has

been included to demonstrate the potential. An example where the technique

could be particularly valuable would be in the analysis of highly successful

attacks by glider borne troops on the Belgian Fortress of Eben Emal in May

1940 (Bierganz and Heeren 1990).

Viewsheds produced with OFFSETB values of 91m (300’) will therefore

indicate the points at which the gunner will be able to see his descending targets

and set up to give them a hostile welcome. It was with this in mind that the

viewshed, Figure 23 overleaf, was created.

33

Figure 23: Viewshed: Attack from the air

It is of interest to note the arc of dead airspace lying in front of the pillboxes

caused by the vertical restrictions of the embrasures. The Vickers emplacement

has a fairly large opening, therefore the view at 300’ from such a building is far

greater than would be possible from the smaller embrasure of a Type 24. The

34

increasing depth of red shading, illustrating areas with less emplacements able

to see the area is a useful tool in predicting areas with decreased risk to

parachutists, although caution must be exercised here – this may be an artefact

of ‘edge effect’ – the non-inclusion in GIS calculations of emplacements lying

beyond the edges of the study area, which still have influence over it.

Also worthy of mention is the patch of dead ground to the west of NV18 and

NV19 (to the left of the image). This area is shielded from view by an area of

woodland, highlighted in a deep red indicating its visibility from some eight or

nine gun emplacements. If it had been the case that the area was only defended

by the Vickers machine guns, this would be an area in which parachutists could

be successfully landed without fear of being spotted (whether or not the aircraft

dropping the soldiers would be visible, is a different matter, beyond the scope of

this example). This conclusion emphasises the importance of negative data in

military archaeology.

‘Dead ground’ - where a defender cannot observe – is a benefit to the enemy,

and likewise, ground that cannot be seen by the enemy is a benefit to the

defender. In this latter case, it might allow the defenders to supply their

positions, move up reinforcements in ‘covered approaches’ or to prepare further

positions or obstacles out of view of the enemy on the ground. The term ‘dead

ground’ is obviously relative to a particular observation point. What a soldier on

the ground cannot see is in ‘dead ground’ to him but it may be clearly visible to

an observer in a high building and therefore not in ‘dead ground’ to the latter.

These techniques are as valid for the study of a medieval castle or Iron Age

hillfort as to the study of the more recent past.

Returning to the matter in hand, it is evident that the modelling technique

described above also works with Type 24 pillboxes and anti-tank gun

emplacements, which, whilst not necessarily equipped as well as a Vickers

emplacement to deal with such an attack, would have been able to fire on

paratroops with light machine guns from within the pillbox or rifle from the

troops outside, so would also have been appreciative of forewarning and a view

of the sky. This technique of analysis is better suited to other anti-invasion

defences such as those on airfields, although their absence in the study area

dictates the use of Vickers emplacements to demonstrate this technique, also

35

valid for use on anti-aircraft guns, searchlight sites and radars. The concept

could also be used to indicate the range at which low-flying reconnaissance

aeroplanes and other enemy aircraft would have come into view over the terrain.

Dive-bombers such as the Stuka, had an exceptionally steep angle of attack

against targets and are therefore unlikely to have been shielded by terrain in

their high altitude approach run, before diving steeply onto their chosen target

(See also Langdon-Davies 1942: Section XII: Anti-Aircraft).

The analysis of Second World War airborne attack scenarios using viewshed

techniques has been proven to be very successful. The presence and absence of

vision in a defensive situation are incredibly useful factors to the historian and

archaeologist alike, and their use is most definitely not restricted to the study of

the Second World War.

36

Artillery Observation Posts ‘In some instances, visibility can be regarded as a key factor in attempting to

answer the question as to why a particular site is in a particular place, rather

than all the other places it might have been located’

(Wheatley and Gillings 2002:202)

Whereas in other disciplines of archaeology, site location often depends on

many factors, ranging from proximity to water and food, to distance from

symbolic sites, military sites are often chosen only for one – visibility.

Soldiers defending the Taunton Stopline would not all have been posted in

pillboxes, defending the immediate frontier. Situated behind the line would be

artillery batteries designed to bring heavy fire down on attacking forces from a

distance.

Each of the six brigades earmarked for deployment along the Taunton Stop

Line, was to be supported by a Field Artillery regiment consisting of two

batteries. Each battery consisted of twelve weapons (Hunt Unpublished-a) – a

mixture of 18pdr guns and 25pdr howitzers. In artillery terminology, a gun is a

weapon with a high muzzle velocity, which can fire over a long range, with a

comparatively flat trajectory whereas howitzers have less of a muzzle velocity

but a very high trajectory (see Complex Firesheds below for further definitions

of military terms).

‘The gun has a longer range and a more rapid rate of fire than a

howitzer of corresponding classification; the howitzer has a

greater shell power and the ability to search ground behind

cover, which guns owing to their flat trajectory cannot reach.

Howitzers can be brought into action almost anywhere, e.g.

directly behind steep ground, buildings, or woods; positions for

guns are much harder to find, since it is necessary to ensure that

their flat trajectory will clear the crest of any high ground or

obstacle between gun and target (this factor is known as “crest

clearance”).’

(War Office 1935:10)

37

Figure 24: A 25pdr weapon in use (Anon 1942)

Figure 25: Trajectories of guns, howitzers and mortars (David Hunt)

When used in a defensive situation, the Field Service Regulations manual (War

Office) gives the following roles for the application of artillery weaponry:

i. Counter-preparation – fire directed on the enemy’s forming-

up places and forward communications, so as to disorganise

and, if possible, break up an attack that appears to be

imminent.

ii. Defensive fire – against troops engaged in an attack, usually

targeted at pre-arranged areas, in coordination with other

weapons (i.e. the Vickers Medium Machine Gun in the

Taunton example), on a pre-arranged signal [for example a

38

rocket or ‘Verey’ light – see also War Office Tactical Notes

for Platoon Commanders (1941)].

iii. Anti-Tank defence – a second line of fire if enemy tanks

breach the front line.

iv. Counter-battery – fire directed at enemy artillery.

v. Harassing fire – to hinder progress in attack and destroy

attacker’s morale by preventing or hampering movements of

reinforcements, food and ammunition to the front line.

As artillery batteries were situated behind the line, often out of direct sight of

the enemy, there were limitations to the effectiveness of the weaponry in all of

the scenarios above if observation and communication was poor. To combat this

factor, observation posts (OPs) were established on high ground at some

distance from the guns to act as the eyes of the gunners. Each battery could

deploy one OP but may temporarily deploy a 'subsidiary OP' to cover areas not

visible from the main OP. In addition, the excellent communication of the OP

(compared with those of a 1940 infantry battalion) would have enabled it to

rapidly pass valuable intelligence rearwards up the chain of command (Hunt

Unpublished-a).

The Roles of Artillery Observation Posts (from War Office 1939)

1. Observation and control of artillery fire

2. Study tactical situation

3. Pass information about enemy and own troops to higher

command

The importance of the OP is highlighted in the Field Service Regulation manual

in that ‘If the enemy can be actually seen attacking, they will be engaged with

defensive fire by all batteries whose observers can see them, although the pre-

arranged signal [see ii. above] may not have been given… Since artillery is

normally placed in indirect positions… the selection of …OPs and the

establishing of communication between the OPs and the guns is often the

determining factor in the time taken by artillery to open fire’ (War Office

1935:12-13). Note that, provided both the gun position and the position of the

target are accurately known, it is possible for the guns to engage the target with

a ‘predicted shoot’. Wherever possible, an OP would adjust such fire onto the

target.

Documentary evidence for the artillery OPs on the stopline is vague when

giving locations – the surviving document (Division North 1940) mentions 1/25,000 sketch maps, although these have not survived. In the same document,

each OP is given a general location and a list of points it can see. This is

currently the only known evidence for the study area OPs (Note that the grid

references relate to the wartime Cassini grid and not the Ordnance Survey

National Grid):

(B) Brigade. Battery. O.P. Visibility from O.P. No. 1. 2 O.Ps North Approaches to obstacle about & South of 1 mile North & South of road at DURSTON. DURSTON. No. 2. KNAPP. From DURSTON to NEW BARN 7345. (C) Brigade. Battery. O.P. Visibility from O.P. No. 1. CRIMSON HILL From STONY HEAD 7344 to

northern slope CRIMSON HILL.

39

Figure 26: Extract from Division North Artillery Plan (1940)

A trial-and-error process was used to suggest accurate locations for these OPs,

using a combination of OS map data, air photographs and the DEM. The

elevation model was examined for the highest ground at each locality. The area

was checked for suitability using maps and air photographs (i.e. the elevation is

not ‘falsely high’ due to the presence of woodland or post-1940s structures or

earthworks), and if considered viable, a point was created and a 360° viewshed

calculated with an observer height (OFFSETA) of 1.6m, to account for a man

standing. This was compared with the Division North Artillery Plan (Figure 26

above) for conformity. When the viewshed was not sufficient to cover the areas

mentioned, another point was chosen and the procedure repeated until sufficient

results were found.

40

Figure 27: Viewsheds of incorrect and correct locations for Knapp OP

In addition, the resultant viewsheds were modified to reflect the distance from

the OP on the basis that the further the point was from the OP, the less easy it

would have been for the observer to identify camouflaged troops or to identify

hostile activity. This was carried out using ArcGIS Spatial Analyst. A ‘distance

to…’ calculation was used to produce a raster in which each cell contained its

distance from the OP. The viewshed, being a binary dataset (0 = invisible, 1 =

visible) was multiplied pixel by pixel, by the distance calculation using the

raster calculator. This resulted in the same distance raster cropped to only the

visible cells of the viewshed. All other cells had a value of zero. In displaying

the resultant raster, it was possible to use this classification (i.e. to use a

graduated fill, the level of which depended on the pixel value, or to create bands

of colour for certain distances) or to display it as a conventional viewshed, using

one colour for a value greater than one4. The distance viewsheds can be

interpreted in one further way – as indicating towards the quality of view. The

further away something is, the less clarity it has, even when viewed through

binoculars. For this reason, the following viewsheds of the estimated positions

4 It is not possible to calculate a cumulative viewshed from this using the

conventional technique, and for this reason, it is recommended that the original

viewshed is retained.

41

of the OPs are displayed with green fading to red. Green indicates good clear

vision, whereas red indicates a deteriorated view due to the longer distance.

Figure 28: Durston OP viewshed

42

Figure 29: Knapp OP viewshed

43

Figure 30: Crimson Hill OP viewshed

One final image was produced using a cumulative viewshed from all OPs. This

is to show dead ground (areas invisible to observers). When studying defence

works, negative data is as important as positive data. Dead ground is ground in

which the enemy can hide from the view of the observer, be it for

reconnaissance, to group before an attack, or to rest after fighting. Dead ground

44

is a risk to the defending troops. Whereas all dead ground behind the stopline

can be ignored, there are some glaring holes in the cover on the non-defended

side. The area southeast of the Crimson Hill OP, flanking the northern side of

the Crimson Hill ridge, is an ideal corridor for attackers to use in order to get

close to the Stopline. Again, a corridor running right up to the line can be seen

0.5km south of Lillesdon. There are also significant areas of dead ground to the

southwest corner of the study area in which large armies could assemble unseen

in readiness for an assault on the Stopline. Whether an enemy could have

identified these covered approaches from the map or by reconnaissance, is

another matter. Nevertheless, they clearly indicate points where the OP could

not observe and report movement or engage with artillery fire.

45

Figure 31: Viewshed of all OPs

46

Figure 32: Dead ground from all OPs

It should be noted that many of these areas of dead ground, especially those

close to the line, would have been covered by fire from pillboxes and gun

emplacements on the line itself. No one aspect of the defences was intended to

operate alone, and mutual support between permanent and mobile units would

have ensured any gaps were well covered. Also worthy of note is that an OP

47

was located at Beer Crowcombe, just southeast of the study area, which was

intended to cover the large area of dead ground on the plateau to the east of the

Crimson Hill scarp round to Ashill.

In a defensive position, fields of fire should normally overlap (War Office

1941), and the areas where there is the greatest overlap may give some

indication of where the planners of the defences considered the threat to be

greatest. Conversely, where the overlapping is minimal or non-existent, it may

identify areas where the perceived threat was lower or there were simply

insufficient troops available to cover it. In this case, examination of viewsheds

may show whether the area of weakness could be observed so that a patrol

could be sent out to intercept the enemy or artillery fire directed onto the

attackers. Here the artillery observation viewshed might give an indication as to

whether the Artillery OP would be able to observe the enemy movement and

call down fire and direct it onto the target.

A GIS such as this can therefore be used to help accurately predict the location

of poorly defined observation posts, providing the terrain model is accurate for

the time period under consideration (see Fisher, P 1991). It gives an excellent

indication of where artillery OP could observe the enemy, report their

movements and engage with artillery fire and, equally important, the areas

where this would not have been practical.

48

Fireshed Analysis A major part of this study was the formation of a methodology for modelling

the theoretical fields-of-fire of the various weapons used on the Taunton

Stopline in a 1940 anti-invasion defence scenario. Due to the reliance of the

methods developed on viewshed calculations, this analysis has been entitled

‘fireshed’. A fireshed indicates the areas that the field-of-fire for a given

weapon at a given point will cover (i.e. a specific target can be engaged by the

given weapon).

Two types of fireshed analysis were developed, each applying to weapons with

particular characteristics. Simple firesheds were developed for weapons that are

fired only at targets that can be seen. Complex firesheds were developed for

weapons fired at targets that are not in a direct line of sight, but can still be hit

providing the coordinates of the target are known (indirect fire – see War Office

1937:5).

49

Analysis of Anti-Tank Weapons ‘The weak points of the German tank are six in number.

(a) Its Blindness. The only view obtainable is through the

driver’s slit, the gunner’s slit, and the commander’s

slit, all of which are very cramped, or the periscope

which can be smashed with small arms fire.

It cannot see anything above itself… It cannot see the

ground anywhere within fifteen feet of itself… In order

to increase visibility tanks often move with the lid open.

(b) Field of Fire. The tank’s guns cannot be lowered to

shoot anything on ground level within twenty feet of the

tank, and they cannot be raised more than twenty-five

degrees upwards… Tanks’ gun-turrets revolve very

slowly and their weapons defend the vehicle from

attack only along their immediate line of sight. Attack,

therefore, from several points at once, must find gaps

in the tank’s defence.

(c) The Tracks. The tank is only useful so long as it can

move: and it can only move so long as the tracks work.

The tracks are very easily broken, and for this reason

anti-tank attacks should usually be concentrated on

breaking the tracks.

(d) Inside the Tank. The living conditions inside the tank

are cramped, very hot, and therefore very exhausting.

No tank crew can remain for more than a few hours

inside a closed tank… If tanks can be kept under

observation… there is bound to come a time when the

crew have to come out; and then they are very easily

destroyed.

(e) Petrol. The tank is, of course, entirely dependent upon

its petrol supplies. These are often brought with it in

50

petrol lorries, which can be easily set on fire with

proper ammunition…

The tank must be prevented at all costs from any

chance of refuelling by the wayside…

(f) Night. Darkness is the greatest ally of the tank hunter.

As night approaches tank crews seek harbours where

they may lie up and rest. This is the opportunity for

stalking, sniping and attacking with grenades and

incendiary bombs.’

(Langdon-Davies 1942)

Whilst the obstacles of the Taunton Stopline were designed to stop the progress

of tanks, it would not destroy them, and would effectively leave a row of enemy

guns pointed at the defending force. Tanks needed to be destroyed, and for this

purpose, anti-tank guns were employed.

As can be seen from the quote above, a tank is similarly restricted both in vision

and fire to a pillbox. The latter has the advantage that it can be easily hidden

until needed, and that the gun crew know the terrain in advance, and the former

has the overwhelming advantage that it is mobile. It is much harder to hit a

moving target, particularly one moving ‘tactically’ so that it makes the best use

of any cover offered by the terrain.

The passage of tanks throughout the countryside would have been made

difficult by the use of many ‘passive’ defences such as anti-tank ditches and

obstacles, and roadblocks. These would funnel tanks into areas in which they

could be attacked easily by troops defending the line. Anti-tank guns were

situated primarily on the main routes of passage or to cover areas where the line

was considered weak.

51

Figure 33: Types of anti-tank ditch (Lowry 1996:89)

Static anti-tank guns on the Taunton Stopline were primarily the 6-pounder

6cwt Mk II Hotchkiss static-mounted ex naval gun (6pdr). These were

reconditioned First World War naval guns of the same variety used in the Mk I

Tank, also of First World War vintage, mounted on specially made steel

pedestals inside covered concrete pits (6pdr emplacements). ‘Every gun was

52

supplied with 50 rounds of ammunition and a crew of 2 Non Commissioned

Officiers (sic) and 8 Gunners organised to be self-contained in an emergency

with at least 4 days hard rations’ (Alexander 1998).

Figure 34: 6pdr Anti-Tank Gun, Royal Armoured Corps Tank Museum, Bovington (adapted from Tank Museum photograph)

These guns were capable of firing beyond 8000yds (7315m, Royal Armoured

Corps Tank Museum pers. comm.) although for maximum accuracy 6pdrs on

the Taunton line were restricted to firing on targets within a range of 600yds

(549m) as the ‘first shot must be a hit and fire must be withheld until a hit is

certain…’ (Southern Command 1940). In order to locate a tank before it came

into range, and to identify it as hostile, gun crews needed to be able to see

further than this. Up to a range of 600yds, a 6pdr trajectory was for all intents

and purposes, flat and had a reasonable probability of hitting the target provided

that the gun sights had been set to the appropriate range. Anti-tank guns were

always only used in direct fire, where the gunner could see and ‘lay on’ the

target. Thus, calculation of a fireshed for a 6pdr emplacement does not require

any consideration of the trajectory. A viewshed with the desired target height

(OFFSETB) is calculated, cropped to a radius (RADIUS2) of 549m.

The second weapon used on the Taunton Stopline, capable of attacking

armoured vehicles, was the Boys 0.55” Anti-Tank Rifle. These were

specifically designed, with a firing rate of nine rounds per minute (War Office

1942b), to combat German tanks developed at the end of the First World War,

but was found less effective against the newer, thicker-armoured tanks used by

the enemy in the late 1930s and 1940s. Each infantry battalion should have had

between 17 and 21 Boys Rifles but many were lost in the May 1940 withdrawal

53

from Dunkirk. Despite their lack of penetrating power, ‘from very close range,

firing from a predetermined firing position in a pillbox, the Boys was still quite

a deterrent against thin skinned armoured cars forced to a halt by road-blocks

and anti-tank ditches’, and despite its growing obsoleteness, ‘it was still the

only reliable anti-tank weapon the infantry could hope to have at hand’

(Alexander 1998). Again, to ensure maximum penetration on the vulnerable

parts of the tank, the range at which infantry were told to limit their fire was

300yds (274m – War Office 1942b). Calculation of a fireshed for a Boys rifle

does not require any consideration of the trajectory and is also very

straightforward. The procedure is the same as dictated for the 6pdr above,

although the RADIUS2 value is restricted to 274m.

Figure 35: Boys Anti-Tank Rifle (David Hunt)

Tank target zones

Approximate ‘kill zones’ (i.e. where to hit the tank to be sure of immobilisation

and / or destruction) of World War II German tanks were located generally

around weak points in the fabric of the vehicle. A guaranteed immobilising

move is to remove one track, thus the tops of tracks and the track return rollers

are prime targets for anti-tank fire, but an immobilised tank (or ‘M-Kill’) can

still fire on the defences. Other points include the turret ring , where the turret

rotates on the hull, areas in which the armour is thinner, or where existing

openings can be found (i.e. around protruding guns, engine and hull air intakes).

These were more likely to result in destruction of the tank or a K –Kill. A

contemporary British diagram illustrates them thus:

54

Figure 36: Vulnerable points of German tanks (adapted from VIII Corps Unknown)

Based on this information, anti-tank firesheds are calculated with target heights

as listed in Table 3, below.

Target Height (OFFSETB, in

m) Description

0 Anything from ground level up – all of the tank would be vulnerable

1 The top of the tracks (main target zone) to the top of the turret – main vulnerable points all covered

Table 3: Anti-Tank Target Heights

55

Anti-Tank Fireshed calculation procedure in ArcGIS:

Produce viewshed from axis of gun with the following settings (assuming

standard Taunton Stop Line gun emplacement – for non-standard designs,

values will require recalculation.

6pdr emplacement:

AZIMUTH1 = [axis of fire] - 90

AZIMUTH2 = [axis of fire] + 90

OFFSETA = [height of gun barrel in m] = 1.6

OFFSETB = [target height – see Table 3]

VERT1 = [maximum elevation of gun barrel from

horizontal] = 90

VERT2 = [minimum elevation of gun barrel from

horizontal] = -90

RADIUS2 = [maximum permitted range] = 549

Boys emplacement:

AZIMUTH1 = 0

AZIMUTH2 = 360

OFFSETA = [height of gun barrel in m] = 1.35

OFFSETB = [target height – see Table 3]

VERT1 = [maximum elevation of gun barrel from

horizontal] = +5

VERT2 = [minimum elevation of gun barrel from

horizontal] = -5

RADIUS2 = [maximum permitted range] = 274

The resulting raster displays the fireshed from static anti-tank gun positions.

56

Figure 37: Screen-shot of newly-created fireshed, ArcGIS

57

Analysis of Anti-Tank View and Firesheds

Figure 38: 6pdr anti-tank gun fireshed, Crimson Hill

As can be seen from Figure 38 above, the Wrantage area either side of the

current A378 (in 1940 the B3153) had very good 6pdr anti-tank coverage at 1m

target height. The great deal of overlap between guns MAT603 and MAT604 on

the flat, open ground on the Crimson Hill plateau give an impermeable area in

which each gun can support the other if under attack. A large area of dead

ground is apparent below the Crimson Hill scarp face. This is less of a problem

than it seems, as tanks would have been totally unable to climb the steep face or

58

traverse laterally along the hillside in this area due to its steep topography and

dense woodland.

Figure 39: Dead ground, southwest of MAT602

The main weak point demonstrated is the patch of dead ground stemming from

farm buildings, leading southwest away from MAT602, at the foot of the hill

(Figure 39). Analysis of the viewshed of these sites (Figure 40), shows that this

corridor is up to 0.5km wide in places and runs approximately 2km to a large

band of dead ground lying parallel with the Stopline which could easily be used

as a hidden passageway right to the defences by an attacking army. Of

consolation is the fact that the northeast limit of this dead ground, on a bend in

the road, two guns have overlapping arcs of fire. The close range to the

pillboxes at this point would also place the tank in a very vulnerable position as

it can only engage one target at a time. Tanks never advance alone for this very

reason (Hunt 2003). At this time, the gun not being aimed at by the tank can

destroy the vehicle. Defences should normally be sited to allow mutual support

59

between the pillboxes containing the weapons (i.e. one pillbox is able to fire on

enemy directly attacking the other) and these techniques enable this principle to

be tested (War Office 1941).

Figure 40: 6pdr emplacement viewshed, Crimson Hill

On the negative side, a single tank would never attempt to breach the line alone

and those following behind will a) be able to see the location of the 6pdr

emplacement when it fires on the first tank, and b) be in a position to retreat

quickly to the dead ground area and plan its retaliation. This would no doubt

60

result in a close-quarters direct-fire fight, which, it is thought, the 6pdr

emplacements could not win (Hunt 2003).

However, it is not the case that 6pdr emplacements would be fighting alone in

defending the Stopline. Adding to the equation the view and firesheds of the

neighbouring Type 24 pillboxes, with their Boys anti-tank rifles, the situation is

greatly improved. It can be seen from the images below that the only significant

ground dead to fire is that of the Crimson Hill scarp face, which is not passable

by tank, although the viewshed with a target height of 2m (the top of a tank)

shows that a tank anywhere on the ‘dangerous’ side of the stopline would have

been visible, and able to be tracked until within range of the guns.

In the example of the Taunton Stopline, it should be noted that the German

army was highly skilled in massing armoured vehicles once they found

opposition that they could neither rush through nor bypass. They would use

sheer volume of armour to punch through the line, as the presence of a great

many simultaneously moving targets would overwhelm the small number of

6pdr and Boys guns in the area. Tanks would move in tactical bounds between

points of dead ground, with one troop or squadron covering the other as they

advanced at top speed to the next patch of dead ground. A good defence system,

therefore, covers most, if not all, of the dead ground. Coupled with this intensity

of armoured attack, Stuka dive-bombers would have attacked gun

emplacements (hence the concrete canopies erected for 6pdrs). See Appendix

IV for a background to German attack tactics.

Overall, it can be seen that the modelling of viewsheds and firesheds of anti-

tank weaponry can give a good insight into the strengths and weaknesses of the

defensive position and assist in deducing the possible strategy of a defended

area. It must be remembered that ideal circumstances rarely exist and most

defensive plans are a compromise. The examples above show that where gaps in

cover by one kind of weaponry exist, they may well be covered effectively by

another, making a significantly better ‘tank stop’ (to use the 1940 terminology)

to invading tanks, that might otherwise be unnoticed by the archaeologist or

historian.

61

Figure 41: 6pdr and Boys fireshed, Crimson Hill

62

Figure 42: Anti-tank viewshed, Crimson Hill

63

Analysis of Rifle Fire

Figure 43: SMLE rifle (David Hunt)

Developed in the 1890s, the Short Magazine Lee Enfield rifle (SMLE) was the

standard service rifle of the British Army during both World Wars. It used the

standard .303 cartridge format, also used in the Bren Light Machine Gun and, in

a somewhat modified form, in the Vickers Medium Machine Gun. The role of

the SMLE on the Taunton Stopline was entirely anti-personnel. The rifle would

be fired from infantry slit-trenches and from pillboxes, such as the Type 24. It

was not normally to be used as an offensive weapon from the loopholes of the

Type 24, as the soldiers were dug in around the pillbox (War Office 1941), as

the loopholes offering the best arcs of fire were occupied by the Bren Light

Machine Gun (LMG) or Boys Anti-Tank Rifle.

Calculating SMLE Firesheds

The SMLE was, like the 6pdr and Boys rifle, a weapon fired directly – i.e. only

at visible targets. Its fireshed, therefore, is calculated along the same lines as for

the aforementioned weapons, by producing a cropped viewshed. In order to

obtain a reasonable maximum range of fire, rifle range target data was obtained

from ‘Small Arms Training Volume I, Pamphlet 1’ (War Office 1942d) which

stated that a first-class shot can hit a 12” (30cm) diameter target consistently at

a distance of 200yds (183m). Taking an estimate of the width of a man’s chest

at 18” (45cm), simple mathematics dictate that the same first-class shot could

hit a man consistently at 300yds (274m). This was later confirmed in Pamphlet

3 of the above series, which instructs that a rifle should not normally be used at

a range greater than 300yds on a moving human target.

In order to calculate a SMLE fireshed in ArcGIS, guidelines should be followed

as for Boys rifles, detailed above, with the following modification:

RADIUS2 = 274

64

In addition, as the weapon was used in an anti-personnel role, its target heights

varied from that of anti-tank weaponry, as can be seen in Table 4.

Target Height (OFFSETB, in

m) Description

0 Ground level – target is 100% vulnerable to fire 1 Man crawling, or running in a crouched position

1.6 Man standing Table 4: Target Heights for SMLE Fire

Firesheds for SMLE rifles along the Taunton Stopline are incorporated in a general Type 24 fireshed, which can be found on page 67.

65

Analysis of the Bren Light Machine Gun

Figure 44: Bren LMG (War Office 1942c)

The Bren Light Machine Gun (LMG) was introduced to the British Army in

1938 and used the same .303 calibre rounds as the SMLE rifle. The gun was

mounted on a bipod (Mk 1 guns featured telescopic legs) and was to be used

(subject to availability following Dunkirk) in every Type 24 pillbox on the

Taunton Stopline, as an anti-personnel weapon (see also Fisher, R 2003 for a

history of the Bren LMG).

The Bren LMG, like the Boys Anti-Tank Rifle, the 6pdr Anti-Tank Gun and the

SMLE rifle, was a direct fire weapon. Although the sights could be set to 2000

yds (or 1800 yds – Mk II gun) it had a recommended range of 600yds and a

maximum practical range of 1000yds (549m and 914m respectively – Hunt

2003).

The Type 24 pillbox was primarily designed to protect the Bren LMG or Boys

Anti-tank rifle. Each of the 5 forward loopholes was provided with a slot to

accommodate the front leg of the Bren tripod. The Bren, when mounted on the

tripod, had an arc of fire that was restricted to 38° – much narrower than the 50º

permitted by the Type 24 loophole (War Office 1942c).

66

Figure 45: Bren LMG on tripod (War Office 1942c)

1. There are five tripods for LMGs to each infantry company; one

with each platoon, the other two with company headquarters

for allotment to platoons as required. Normally tripods are

used only in defence.

2. The use of the tripod is twofold :-

i. To enable the gun to fire on a fixed line.

ii. To enable it to fire within the limits of a fixed arc.

Apart from these uses, the gun will normally be fired from the

bipod, because of the far greater flexibility with which it engage

targets in different directions when thus mounted. (War Office

1942c)

Areas of dead ground between the arcs of fire from adjacent pillbox loopholes

exist, although each pillbox is unlikely to have been manned by more that a

couple of LMG. It was commonplace to remove the gun from the pillbox and

set it up close by, in order to cover this dead ground (War Office 1941). The

five-metre resolution of the DEM dictates that in order to affect the view and

firesheds produced, the gun when arranged thus, would need to be in a separate

cell from the pillbox, which could be up to five metres away. For this reason,

all-round coverage is assumed from the pillbox site. Viewsheds are calculated

on the same basis as for the SMLE rifle, with a RADIUS2 value of 914m.

67

Figure 46: Type 24 view and firesheds

The above fireshed was produced by creating a cumulative viewshed of Type 24

pillboxes on the Taunton Stopline, ignoring those forming part of anti-tank

islands as these were a later addition in 1941. The viewshed had a target height

(OFFSETB) of 1m and a RADIUS2 value of 914m (the maximum practical

68

range of a Bren LMG, and the general area of interest of the infantry soldiers

with both Boys and SMLE rifles Hunt). In order to display a banded result, a

distance calculation (see Complex Firesheds below) was also carried out on the

points. The viewshed was reclassified using ArcGIS Spatial Analyst into two

classes: 0 = 0, >0 = 1. This process converted the cumulative viewshed, with

values reflecting the number of pillboxes able to see the point, into a simple,

visible or invisible classification, and when multiplied by the distance

calculation, as for the creation of ‘quality of view’ viewsheds, resulted in a

raster in which every pixel of visible ground contains its distance from the

nearest pillbox. This raster was cropped to exclude data on the eastern side of

the line. The raster was displayed with its distances up to 300yds / 274m

coloured green, up to 600yds / 549m coloured yellow and the final band, up to

1000yds / 914m, coloured red.

In the green band, all weapons are effective. This is also the only band in which

tanks are vulnerable, due to the presence of the Boys rifle. Enemy Infantry are

also exposed, as they are susceptible to fire from both the SMLE rifle and the

Bren LMG. The yellow band indicates the usual operating range of the Bren,

and the red, the maximum range of the Bren and the area of interest for

observation by troops in or around Type 24 pillboxes.

Immediately apparent from the fireshed is the large (0.5km wide) gap in the

green band mid-way along the southern arm of the stopline. This gap is out of

range of Boys rifles, meaning it is easily permeable by tanks, unaffected by the

smaller calibre weapons that do cover the area. A similar, although smaller, gap

exists 0.25km east of Lillesdon, and a larger gap can be found at the northern

limit of the study area at Durston. Here, lying just beyond the northern boundary

of the study area, a 6pdr anti-tank gun stood which would most probably cover

this sufficiently. The former two gaps, however, are ideal for the attackers to

penetrate and double back to destroy the surrounding pillboxes from their

vulnerable side (see Appendix X for details of German attack tactics, and War

Office 1937:109-10 for British tactics in the same situation).

Also apparent are patches of dead ground, especially in area north of Lillesdon.

Some of these form corridors along which tanks and infantry could advance

unseen. In general, excepting this dead ground, there is good anti-personnel

69

cover to be found all along the line in the study area, although the Crimson Hill

plateau appears to be weakly covered. Again, overlapping cover from pillboxes

situated outside the study area may cover this ground, and the Vickers machine

guns also situated here to the south of Beer Crowcombe would enhance the

defence a great deal.

A point worthy of note is that this fireshed is not accurate around Lillesdon, in

that it would be impossible to obtain a direct line of fire through the hamlet due

to the presence of buildings, which would significantly reduce the viewshed at

this point. An area for future work is in digitising every building in a study area,

and measuring and assigning accurate heights to said structures. Also absent is

tree cover along the canals that form the main obstacle. Air photos failed to

reveal the density (and in some cases, presence) of trees along much of the

length of the canals, and therefore they were not digitised.

Despite these inaccuracies, this does prove that calculating firesheds for direct-

fire weapons is possible using viewshed techniques, and, given accurate

elevation data, the method can be applied to many situations throughout time.

70

Complex Firesheds: Trajectory Modelling Modelling ballistic trajectories using GIS viewshed techniques has never before

been documented. This study is breaking new ground with the development of a

technique intended to analyse the fields of fire of historical weaponry in a three

dimensional, geographical nature. The technique is applicable to any projectile-

launching weapon of any period, providing range tables such as Table 6 below

are present or can be produced.

The method is ultimately useful for the modelling of firesheds of weapons used

in ‘indirect fire’ – that is to say firing at points the gunner cannot see. This could

be, for example, on ‘fixed lines’ or ‘fixed arcs’ through fog, smoke, or at night

provided preparation has been carried out in daylight (War Office 1937:4). The

only infantry weapon, capable of indirect fire, used in permanent fortifications

on the Taunton Stopline was the Vickers Medium Machine Gun. The Bren

LMG when mounted on its tripod could be fired against targets temporarily

obscure by fog, smoke or darkness but could not practically fire against targets

outside its field of view.

A more complex case is where the target is hidden behind the crest of a hill and

the weapon has to fire over the crest. The weapon obviously has to know where

and when a potential target appears if it to attempt to engage it. The field

artillery supporting the garrison of the line would normally have fired from

concealed gun positions in the indirect mode against targets that could not be

observed from the gun. This analysis has only been applied to the Vickers

MMG as no accurate locations for artillery batteries are known.

The Vickers Medium Machine Gun

Figure 47: Vickers MMG (Anon 1942)

71

The Vickers Medium Machine Gun (MMG) was ‘the most powerful of all

infantry weapons in defence’ (War Office 1937:4). Introduced in 1912, the

MMG was a large, belt-driven gun, capable of firing up to 250 rounds in one

minute (War Office 1937:5). The gun had a variety of mounts, the most popular

being a tripod (Forty 1998:24) on which it stood atop a concrete table in the

Vickers emplacement, with its ammunition and a water canister used for cooling

the barrel, beside it (Alexander 1998:93). The guns were located in pairs along

the stopline as a section of two guns shared a range-finder and fire controller,

usually situated in a slit-trench between the two emplacements (Hunt 2003).

Figure 48: Pair of Vickers emplacements (arrowed), Crimson Hill, viewed from the attacking side (David Hunt)

Vickers MMG ranges were defined as in Table 5 below. Close range fire was

easily directed and somewhat economic in terms of ammunition. Beyond this, a

far greater deal of accuracy and rigidity in control is required in order to

guarantee successful fire. Effective and long ranges both require a greater

amount of ammunition in order to be sure of hitting the target. Above all, it was

important to accurately know the range of the target being engaged.

72

Term Range (yards) Close <800 Effective 800 – 2000 Long 2000 – 2800

Table 5: Machine Gun Ranges (War Office 1937:4)

The introduction of Mark VIIIz streamlined ammunition just before the Second World War enabled the gun to engage targets to 4200 yards (Hunt 2003). Before fireshed calculation methods are discussed, military terminology relating

to general small arms and more specifically to machine guns is listed to aid in

the understanding of further sections.

Small Arms Terminology (Adapted from War Office 1942d)

These terms have been in military use in Britain throughout the twentieth

century. Similar terms are used in other countries.

Line of fire – direction of target from muzzle of weapon.

Line of sight – straight line from firer’s eye through the sights to point aimed at.

Trajectory – curved path taken by bullet during flight.

Culminating point – greatest height above line of sight to which the bullet rises

in flight.

Angle of descent – angle that the tangent to the trajectory makes to line of sight

at point of impact.

First catch – point where bullet has descended sufficiently to strike the top of

the target

First graze – point where bullet, if not interfered with, will first strike the

ground.

Dangerous space – for a given range, is distance between first catch and first

graze. See below.

Tangent angle (or tangent elevation) – angle that barrel axis makes with the line

of sight.

Angle of sight – angle between line of sight and horizontal plane.

73

Crest Clearance Angle – angle by which axis of gun barrel must be raised above

line of sight to crest to ensure all bullets clear the crest.

Quadrant elevation – angle between barrel of gun and horizontal, always above

the angle of sight (see also War Office 1942a).

To summarise; the Dangerous Space depends on the:

• Range

• Height of weapon above ground level

• Height of object fired at (target)

• Flatness of trajectory

• Conformation of ground

The Dangerous Space decreases as the range increases, due to steeper angle of

descent at longer ranges.

The Dangerous Space increases:

• The nearer the weapon is to the ground

• The higher the target object

• The flatter the trajectory

• The nearer the ground conforms to the angle of descent of the bullet

Note that with a gun firing at a set range over flat ground, the bullets should

strike the ground at that range.

Machine Gun Terminology (Adapted from Hunt Unpublished-b, War Office

1942a)

Cone of Fire – When fire is delivered to a target, the bullets pass through the air

in the shape of a cone of fire which is the pattern formed by a series of shots

fired with the same elevation and point of aim. (e.g. Bren LMG – cone of fire is

oval pattern with density decreasing from the centre outwards. Approx size at

500 yds is 6.5 ft W x 7.5 ft H for bursts fired from bipod and 3.5 x 5.5 ft for

bursts fired from tripod.)

74

Beaten Zone – When machine gun fire is correctly applied to a target, the bullets

of the cone on striking the ground form a beaten zone around the target. The

size of the beaten zone will vary with the range and slope of the ground in

relation to the angle of descent of the bullets. Beaten zone depth increases with

range due to increased angle of descent. Beyond 1500yds it increases again;

particularly laterally but, at the same time, the angle of descent becomes steeper

and the dangerous space formed by the lowest bullets of the cone becomes

smaller. (e.g. Bren LMG – at a range of 500 yds, the beaten zone measures

172yds in length by 2yds in width. At a range of 1000 yds, the beaten zone

measures 115yds in length by 4yds in width.)

Effect of Ground on Beaten Zone – A cone of fire striking a steep hillside will

cover a very small area of ground. As the slope decreases, the beaten zone

increases. The maximum occurs when the slope of the ground in the target area

conforms to the trajectory of the bullets. In some cases, the ground may slope

away out of sight of the firer (i.e. a ‘reverse slope’) but still be covered by the

beaten zone. Troops in this ‘reverse slope’ position would be unseen by the firer

but would still be in danger of un-aimed fire from the Bren LMG or indirect fire

from the Vickers MMG.

Permissible Error In Ranging – The error that can be made in range estimation

while still keeping the target in the beaten zone. The centre of the beaten zone

should be centred at the range of the target. The permissible error is therefore

half the beaten zone. As the distance increases, it becomes increasingly

important to establish the accurate range to the target.

Defiladed Zone – The area of ground that would be in the beaten zone but for

the fact that a proportion of the bullets of the cone have met an obstruction,

usually a piece of high ground.

Dangerous Zone – For fire to be effective, the target must be included in the

dangerous zone, which is the area of the beaten zone plus the dangerous space

formed by the lowest bullets of the cone.

75

Figure 49: Applications of Fire (War Office 1942d)

It is, therefore, vital that modelling of the dangerous zone be carried out in order

to assess the effectiveness of, or reason behind, the placing of a weapon. As

essentially, the dangerous zone is defined by the trajectory, this is what is

modelled below.

Roles of the Machine Gun (Adapted from Hunt Unpublished-b)

1. To fire at point targets. (The gunner needs to see the target and to

accurately know the range; particularly at longer distances)

2. To fire on fixed lines producing a long thin fixed 'fence' of fire that will

kill anything walking across the fixed line. Typically the fixed line

might be along the obstacle (e.g. a canal) or down an approach road.

(Here the trajectory matters a lot as at the far end of the line, the attacker

will be shot in the foot, while at the centre of the fixed line, they will be

shot through the head).

3. ‘Sweeping terrain with fire’ so that any soldier moving across that

terrain is likely to be hit. (With this technique, the gun sights are set at

one range (normally 600yds) in the knowledge that the dangerous space

76

is such that a man at any lesser range should be hit). This technique

might be used to deny attackers access to particular areas.

4. To put down a weight of fire on a particular area (e.g. a bridge as a

‘crossing point’ over an obstacle). Here the main effect is the beaten

zone. Outside the zone, towards the gun, there will also be the

‘dangerous space’, which depends on the terrain, range and height of

trajectory above the actual ground.

Modelling a Trajectory using Viewshed Techniques

Upon initial examination, it was considered that trajectories are parabolas.

Being such, they are easy to calculate using a parabola equation such as:

y = ax2 + bx + c

Unfortunately, this is only true for projectiles moving in a vacuum. In reality, a

bullet fired from a gun in the open air loses momentum through the resistance of

the air as it passes through. This produces a curve that starts gently upwards, but

at great speed, and gradually gets steeper as the wind resistance increases. From

the apex of the curve, when the forces of gravity outweigh the upward thrust of

the bullet, to its impact, the curve becomes dramatically steeper in a downward

direction. In a parabola, the upward and downward curves mirror each other.

Consequentially, experiments with parabolas were ended and details of true

trajectories of weapons were sought. The trajectory of a projectile depends on

its weight, the force with which it is launched and the amount of wind resistance

it offers. Trajectory data from various contemporary weapon range tables was

sourced and used in the preparation of firesheds of indirect fire weapons, under

the assumption that there is no wind at the time of firing.

The first stage in modelling the trajectory of a bullet using viewshed techniques

is to restrict the elevation of the viewshed to a one-degree aperture, representing

the line of sight of the gun. As the distance the projectile will travel varies

considerably with the angle of the gun (see Figure 51 – the initial angle of the

trajectory is equivalent to the angle of the gun), it is not suitable to calculate

curved trajectories using the entire vertical field of view from the pillbox

embrasure, as was possible for the flat trajectory and direct-fire weapons in the

previous section.

77

Figure 50: Comparison between parabola and trajectory

Height of trajectory (in feet) above line of sight

at given distance from weapon in yards Range from weapon to

target in yards 0000

0

0000 200

0000 300

0000 400

0000 500

0000 600

0000 700

0000 800

0000 900

0000 1000

0000 1100

0000 1200

300 0 0.7 0 400 0 1.6 1.4 0 500 0 2.6 2.9 2 0 600 0 3.7 4.4 4.1 2.6 0 700 0 4.9 6.2 6.6 5.8 3.6 0 800 0 6.3 8.3 9.4 9.4 7.9 4.8 0 900 0 7.9 10.7 12.6 13.3 12.6 10.3 6.2 0

1000 0 9.7 13.4 16.2 17.8 18.0 16.5 13.2 7.8 0 1100 0 11.7 16.5 20.3 22.9 24.1 23.7 21.3 17.3 10.5 0 1200 0 14.0 19.9 24.8 28.5 30.9 31.7 30.7 27.5 21.9 12.5 0

Table 6: Trajectory Table for Rifle No 1 Mk 3 SMLE firing SAA .303 MkVII ammunition, with muzzle velocity of 2440ft/sec (War Office 1942d)

Note: As the Bren LMG uses the same ammunition as the SMLE, discussed above, its trajectory

is the same. Therefore, the data in Table 6 above is applicable to both weapons. The Bren LMG

manual (War Office 1942c) instructs users to view Vickers Machine Gun range tables, as these

are equivalent. Moreover all three weapons have a similar barrel length. It was assumed,

therefore, that short-range Vickers MMG trajectories are similar to those of the SMLE. This is a

roundabout way of obtaining Vickers range data, but was the only option open as no sources

were able to supply range tables for the obsolete Vickers MMG.

78

SMLE Rifle Trajectory 1942

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

Range (yards)

Hei

ght o

f tra

ject

ory

abov

e lin

e of

sig

ht (f

eet)

Figure 51: SMLE trajectory plot

In order to maximise the dangerous space contained within the height of person,

it was standard procedure to sight the LMG so that its bullets would hit the

ground at 600yds (549m). At this range, the entire height of the trajectory is

within what was considered the average height of a soldier (War Office 1942c).

It must be noted that the range table above is calculated with the gun mounted at

ground level – i.e. zero feet. In use, the gun would, if mounted outside the

pillbox, be supported at a level of six inches to one foot (15-30cm) and when

used inside a pillbox, the gun would be mounted at approximately 1.45m from

the floor of the building (taken as ground level for this study, although some

pillboxes were dug in to hillsides to aid in camouflage). The concept behind

this ranging is that, on flat ground, attackers coming into contact with the

trajectory of a bullet ranged at 600yds would have been hit somewhere on their

body. The closer to the gun they stood, they would be hit in the foot or leg. The

further away they stood, the bullets would hit higher up their body. At the apex

of the trajectory, they would be hit in the head. On the descent of the bullet, they

would be hit from above, gradually lower down their bodies as they increased

their distance from the gun.

As the weapon can still traverse horizontally when its angle is set vertically,

there was no need to restrict the AZIMUTH1 and AZIMUTH2 values more than

the embrasure of the gun emplacement constrained them already.

79

A simple viewshed such as this will not allow for the curvature of a projectile in

motion. Viewsheds are based on sight, and sight occurs in straight lines, which

cannot be manipulated easily. It was considered a more feasible task to alter the

heights of the ground surface to reflect the curvature of the straightened

trajectory. The concept is based on an analogy of the trajectory and ground

surface as being a single piece of rubber, the bottom face of which represents

the landform and the top face of which is curved upwards and then downwards,

representing the path of the trajectory. The process outlined above is simply

demonstrated by pushing down on the top of the rubber until the curved surface

is perfectly flat. Consequentially, the bottom surface will have been pushed

down by the amount needed to flatten the top and will represent the shape of the

trajectory, although inverted. A viewshed carried out on this deformed ground

was therefore considered to be an accurate fireshed for the chosen weapon.

The Simple Model, as created in ArcGIS

The Spatial Analyst distance calculator was used to create a circular raster

centred on a point shapefile representing the pillbox. The radius of this circle

was set to the range being investigated, and the procedure calculated the

distance from the pillbox to each pixel in the raster.

The values in the circular raster were then reclassified using Spatial Analyst into

the distance bands found on the SMLE range table. Each band was allocated the

value of the height of the trajectory at that point. This resulted in a raster made

up of concentric circles, with from the centre out, values that rose gradually then

fell. In effect, this was a circular trajectory around the pillbox point.

The raster calculator component of ArcGIS was then used to subtract the pixel

values of the circular trajectory from those of the elevation model at that point.

Its output, a temporary file, showed the terrain dipping down before returning to

its original level, in a complete circle.

A viewshed was then calculated from the pillbox point. The resulting image

represented the fireshed of the pillbox for the chosen weapon. The viewshed can

be calculated with the standard OFFSETB values explained in previous sections

to gauge the effect of pillboxes against different height targets.

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Figure 52: Original elevation model

Figure 53: Distance raster reclassified into 200yd intervals

Figure 54: Previous raster reclassified with trajectory height above line of sight

Figure 55: Result of subtracting Figure 54 from Figure 52

Figure 56: Viewshed calculated using

Figure 55 as DEM Figure 57: Resulting fireshed, displayed on

original elevation model

Problems with The Simple Model

The simple model produced a fireshed that is inaccurate on two accounts: The

trajectory created was stepped, not smooth, as the path of a bullet flying through

the air should be. This is due to the low resolution of the source data, and was

easily remedied.

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Interim values – x(interim) – were interpolated from the values either side

(upper x and lower x), where the size of interval (gap size) is known, as follows:

gapxinterimxinterimxsizegap

xlowerxuppergapx

+−=

−−=

)1()(

1

(The same formula applies to y values)

The other problem was apparent when the model was implemented on sites with

a difference in height between gun and target. A pair of MMGs at the northern

end of the study area were situated atop a bank, overlooking surrounding

countryside. Those on edge of the Crimson Hill plateau also look out over a

hillside that drops away suddenly. Firesheds from these guns showed no points

of contact at all. Had this been the case, guns at these points would be useless

against anything but falling parachutists. The reason for this error is the

assumption that the line of sight was horizontal, and therefore the trajectory

ended in mid air. Vickers MMGs, however, could tilt up and down to combat

such problems and would range on whatever ground was 600yds away (Hunt

2003). As can be seen from Figure 60 below, the line of sight of the elevated

gunner is angled down towards the target, and the trajectory displayed reflects

this. There is still a lot of dead ground beneath the trajectory of this gun in

which an enemy could move unscathed, although not as much as is present in

the model. A further problem can be visualised in which the target is higher than

the gun. In this instance, a horizontal fireshed would see bullets hitting the

ground below the target, when in reality, the gunner would aim the gun upwards

to counteract this.

Nevertheless, this technique offers the possibility of assessing whether

positioning the gun on the top of an embankment (or on high ground), giving

good fields of view but limited dangerous zones, would be better than

positioning the gun at the foot of the embankment (at ground level) with

reduced fields of view and shorter, but more effective fields of fire.

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Figure 58: ‘Footprints’ of trajectories

It is not enough to subtract a value from the height of the bullet corresponding

to the elevation of the line of sight. The range is measured along the line of sight

rather than the horizontal plane, but the values subtracted from the elevation

model are based on the horizontal ‘footprint’ of the line. At 90° from vertical,

the line of sight and horizontal footprint are equal. At higher or lower angles of

sight, the line of sight does not change length, but its horizontal footprint

becomes shorter. Due to this fact, it was necessary to rotate the trajectory curve

by the same angle as the line of sight.

Figure 59: Right angled triangles reflecting points on a trajectory

In order to obtain the angle of sight, basic trigonometry was used. A plane was

drawn at the target ground level, parallel with the horizontal line of sight. A

vertical line was drawn from this plane to the gun. Upon adding the angled line

of sight, a right-angled triangle is produced. Using sine rule and the knowledge

that when a straight line cuts a pair of parallel lines, the angles between the lines

are the same at opposite ends, the angle of sight was calculated (see below).

Inverted, this system also applies when the target height is above that of the

gun.

83

1

sin−

=

hypotenuseoppositea

Figure 60: Calculating the angle of sight

In order to rotate the trajectory, the straight-line distance was calculated

between each point and the gun, using Pythagoras’ theorem (a2 + b2 = c2), where

c is the point-gun distance, a is the range to the point and b is the height of the

point above the line of sight. The data was then rotated using a standard polar

transformation formula, using Microsoft Excel. Equations for the transformation

are as follows:

( )

−

++=

−− 1122 tansin90sin

xy

hgyxxnew

( )

−

++=

−− 1122 tansin90cos

xy

hgyxynew

Where: g = gun height h = hypotenuse length x = x-axis value y = y-axis value The Advanced Model

In order to calculate a fireshed using the resulting trajectory, it is necessary to

adjust the vertical angle constraints (VERT1 and VERT2) in order that they

reflect the angle of sight. VERT1 is set to the angle of sight, whilst VERT2 is

set to the angle of sight –0.1. The value for VERT2 is fairly arbitrary and can be

adjusted depending on the permutations of the GIS package in use, but should

always be an interval of one degree or less. This is to represent axis of the barrel

of the gun fixed at a certain elevation (and therefore range). Following this

procedure, the fireshed is calculated using the new trajectory data to the same

method as described in ‘The Simple Model’, above.

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As this method involves a great many manual processes, making calculation of

the firesheds of several guns a time-consuming and repetitive process, a Visual

Basic script to automate the process was coded by Graeme Earl, University of

Southampton. This script is included in Appendix V, but can be summarised as

follows:

A ‘personal geodatabase’ (alternative form of vector data storage to shapefiles)

is required containing point data for guns, coded with OFFSETA and B,

AZIMUTH1 and 2, VERT1 and 2, reflecting the desired output fireshed. Also

essential is an elevation model.

The user edits the script, adding file location data for the geodatabase, the

elevation model and a working folder. The (unmodified) trajectory data for the

desired range is added, in either imperial units or metric (a flag is set to instigate

a conversion procedure should it be required), together with the number of new

points to interpolate between each existing point, and finally the angle of sight

is input. On running the procedure, a raster image of a fireshed is produced for

each point in the geodatabase, based upon the constraints entered. In order to

overcome the need to know the angle of sight, a routine was added to allow

repetitions of the script with varying angles of sight – the trajectory being

rotated separately for each iteration of the algorithm. Each fireshed is calculated

on a separate record in the geodatabase, so in order for this to function correctly,

the source file requires consecutively numbered records located on the same

pillbox, with corresponding VERT1 and VERT2 values to the angles of sight

examined by the routine at the time.

This script is a great labour-saving device, well suited to the application of

calculating firesheds for an entire stopline. It is at present, however, limited by

being unable to recalculate VERT1 and VERT2 values automatically, making

large amounts of data redundancy necessary for the production of firesheds for

multiple ranges at one point. This is a trivial point that can be easily overcome

in the future.

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Figure 61: Complex Fireshed of MV1, Crimson Hill

A trial of the automated method on Vickers emplacement MV1, situated at the

edge of the Crimson Hill plateau, can be seen in Figure 61 above. This was

calculated to cover the majority of the vertical limits of the embrasure of a

Vickers box, namely 13° either side of the horizontal, to assess the suitability of

the model for estimating the angle of sight when it is unknown. The total angle

(26°) was divided into eighths, (3.375° each) in order to give overall cover.

The resulting fireshed consisted entirely of dead ground at all elevations but

13°, 9.625° and 6.25°, of which the latter produced the best results. This

suggests that the angle of sight of MV1 would need to be set at approximately

6.25° in order to be effective at 600yds. (NB. The band of dead ground in the

fireshed is caused by the 3.375° gap between calculations and can be reduced by

using smaller intervals).

The small amount of dangerous space highlighted by the fireshed indicates that

this gun was probably used as a long-range weapon, and the location of its

fireshed points towards its role as firing enfilade (i.e. providing a ‘fence of fire’

across the Stopline – see Figure 62, below).

This fireshed does indicate a problem with the Advanced Model. The model

ends at the point at which the trajectory from the range table grounds, i.e.

86

crosses the line of sight. If the gun is being fired horizontally from the top of a

high embankment over lower ground, the bullet would not come into contact

with anything at the end of its trajectory and continue to curve downwards until

it hits the ground some metres beyond. This curve is not recorded in trajectory

tables, but is still an important factor in determining firesheds of high-mounted

weapons.

Despite the fact that these methods are in their infancy, it is most definitely

apparent that it is possible to create credible firesheds using GIS-based

technology that can be used to make assumptions as to the role of pillboxes and

gun emplacements in the study area – a factor applicable to countless other

types of indirect-fired projectile throughout time. Given more development, the

system will become more user-friendly and accurate, making it invaluable to the

military archaeologist and historian.

Figure 62: Theoretical and actual viewsheds, MV1, top of Crimson Hill, suggesting an

enfilade role (green = theoretical arc, red = viewshed)

87

Chapter 3: Discussion of Results This study has opened many new avenues of research to the military

archaeologist. The use of GIS analysis in the archaeology of recent conflict has

a great number of positive points, and this work was unable to do more than

scratch the surface of what could become an incredibly useful and powerful

‘toolkit’ for the researcher.

Credibility of Results In order to assess the credibility of the results, it would be necessary to test them

against real data. As there was no invasion of England and no hostile action in

the southwest of the country, these defences were never tested. For obvious

reasons, it is not possible to re-equip the pillboxes and gun emplacements with

working weaponry and live ammunition, and attack for real using preserved

military vehicles. It is difficult, therefore, to determine the level of accuracy of

the firesheds and viewsheds to the 1940 situation, due to the lack of

contemporary data (particularly elevation data).

David Hunt, retired colonel and military researcher, who has assisted

throughout this study, spent his childhood in the area in the 1940s and 1950s,

and has visited the area regularly since), was invited to review the products. He

queried immediately some early viewsheds leading to revisions of the

vegetation in some areas. He found the revised viewsheds accurately portrayed

the intervisibility and carried out some limited on site checks on the ground in

the area. He then reviewed the later versions for the realism over the assessment

of the terrain by viewshed. All these he found to be most satisfactory within the

limits of summer vegetation in 2003. He then considered whether the firesheds

were reasonable for the weapons concerned, sited in the actual pillboxes and

emplacements. Having visited many of these over the last two years, he was

well satisfied that the firesheds were reasonable. Overall, he was impressed

with the power of the analyses and enthusiastic to become involved in

developing the techniques further and to assess other sections of the Taunton

Stopline.

This sort of outside involvement of an expert, with both local terrain

knowledge, military expertise, together with historical information from

88

research was most useful in ensuring that the results were realistic and gave

confidence that the techniques could be effectively used on sites where such

knowledge is not available.

An overall assumption can be made that the level to which fireshed techniques

as a whole are realistic depends mainly on the quality and temporality of the

elevation model being used. Errors in elevation models, however small, can

significantly affect viewsheds (and therefore firesheds) produced, as explained

by Fisher (1991). Also vital are accurate locations and bearings for weapons,

and in the case of indirect fire weapons, accurate trajectory data, whether

documented or gained experimentally. If applying the method to a more ancient

example, for instance, a medieval trebuchet, it would be impossible to gauge

how accurate the resultant model was, and despite the comparative recentness,

the same is still true for the Second World War.

These analyses indicate some of the strengths and weakness of the Taunton

Stopline fortifications. It must not be forgotten that the planned garrison was

considerably stretched and while a single infantry battalion would have been

responsible for most of the sector from south of Durston to north of Wrantage,

the tactical doctrine of the time was the a battalion position would normally be a

square of 1000 yards (Hunt 2003). The communications of the battalion would

therefore have been severely stretched and much would have depended on the

determination of relatively junior officers and their soldiers to fight to the bitter

end. Equally, experiences in Belgium in May 1940 show how massive modern

fortresses like Eben Emal or Battice, which were considered at the time to be

impregnable, rapidly fell under German attack (Bierganz and Heeren 1990). In

the end, much depends on the skill, determination and bravery of the individual

soldier; together with some luck.

Lastly, when analysing the effectiveness of British anti-invasion defences, the

rapidity of their location, design and construction is a major factor. In 1949,

Winston Churchill wrote: ‘Nothing moves an Englishman so much as the threat

of an invasion, the reality unknown for a thousand years’. This provocation

should not be forgotten. It was a consequence of this threat that although the

reconnaissance for the Taunton Stopline was only made in late June 1940 but by

early August, most of the obstacles were well under way to completion and that

89

by late October 1940 over 300 pillboxes and gun emplacements had been

constructed (Hunt Unpublished-a).

General Conclusions – what the system as it stands is capable of Providing good terrain data for a contemporary period is available, GIS-based

terrain analysis can be used in many ways by the military historian and

archaeologist:

• Reverse engineering methods can be used to find the most likely site for

features like observation posts, where their exact location is unknown,

but their role or requirements are known.

• Reverse engineering can also be used to estimate the most likely

orientation of pillboxes or gun emplacements, where this is not known

due to the demolition of the original structure.

• The primary roles of pillboxes and gun emplacements can be established

by examining their view and firesheds.

• Areas covered heavily with both vision and fire can be pinpointed,

leading to new questions of the reasoning behind this heavy cover (i.e.

what is in need of such a high level of protection).

• Likewise, areas with low cover can be examined and questioned as to

what was considered less important, or less of a risk, to the extent that it

was not defended as well.

• Vulnerable points of defended areas may be identified by the presence of

dead ground in close proximity to the front, and by ‘corridors’ of dead

ground enabling an attacker to get close without detection.

• The potential of field artillery can be evaluated through analysis of the

location and views from its observation points.

• The effect of trees and buildings on visibility and fields-of-fire is

immense and should at no point be underestimated. Likewise, the effect

(and indeed, presence) of standing crop is one that is highly unlikely to

be predictable easily.

90

• Weak points in defended areas may not necessarily have been weakly

fortified, but may be easier to attack due to terrain, vegetation and

buildings providing covered approaches to up to the defences

themselves.

• Similarly, the relative strength of fortifications can be assessed. It may

be the case where two pillboxes cover more ground than their

neighbouring pillboxes, as the ground they cover is relatively flat and /

or devoid of obstructions.

• Defences can be evaluated against the appropriate military doctrine and

tactics of the period and the level to which they comply can often readily

be assessed.

• A military historian can tell much more about a defended area given this

new data. Viewsheds can tell whether defending forces would have had

advanced warning of an attack or whether they were likely to be

subjected to a nasty surprise. They can also show if the attackers would

have a good chance to view the defences and fire at them from a

distance.

Improvements / Future Directions All analysis in the study area is subject to ‘edge effects’ – the distribution of

pillboxes goes beyond the limitations imposed by the study area. Due to this

factor, towards the edges, the viewsheds and firesheds are not as accurate as

those in the middle of the area, as the fields of view and fire of any pillboxes

outside the area, but still able to see it, are not taken into consideration. This

should not be ignored by future users of these techniques as the results produced

from a cropped area can be misleading. Ways around this problem include

careful selection of a study area – ensuring all points for which view and fire is

to be calculated are included, and using a larger DEM and observer point

dataset when calculating cumulative viewsheds, which can then be cropped to

fit the rest of the data (Wheatley and Gillings 2002:209)

Accuracy of the elevation model, and of vegetation and buildings placed

thereon, is a major cause for concern. For example, Hunt has commented that

through personal memory, the trees around the study area were probably not as

91

high as the 30m height assigned to them. Moreover, the differences in visibility

between trees in leaf in summer and trees without leaves in Winter can make an

enormous difference to a viewshed. The quality and accuracy, therefore, of the

digital elevation model is the most influential factor. Variation in elevations,

especially those closer to the observer, can have a massive (and unrealistic)

effect on fields of view and fire (Wheatley and Gillings 2002:209-10). As cited

previously, Fisher comments heavily on the effect of a bad DEM on viewsheds.

His solution to the matter is to use ‘fuzzy’ viewsheds – an element of noise is

added to the DEM before calculation of a viewshed. This noise is then changed

and a second viewshed created. When this process has been repeated several

times, the resulting binary viewsheds are added together. Pixels from the

resulting raster with higher values are more likely to be visible to the observer

point, and conversely, those with lower values are not (Fisher, P 1992).

Application of this system to fireshed calculation (thus creating ‘fuzzy

firesheds’ would aid in making more accurate assumptions of the probability of

being hit by fire in a certain location, rather than a possibly quite inaccurate yes-

or-no situation.

A more accurate contemporary elevation model could be obtained using

photogrammetry of stereo pairs of 1946 air photographs. This would, of course,

be subject to the same errors in accuracy mentioned elsewhere, but would aid in

the accurate study of an area. Although largely unaltered, the present study area

is cut briefly in the northwest corner by the M4 motorway, where the ‘shadow’

beyond the motorway embankment is clearly visible on the elevation model

(Figure 6), and by urban growth in areas such as Lillesdon. A contemporary

DEM would, obviously, exclude these factors, and could easily be made to

show actual heights of woodland, hedgerows and buildings without additional

(and error-prone) digitising.

It is almost impossible to predict such variables as restrictions to view imposed

by crops. For example, in the summer, a standing crop of wheat or barley would

be able to hide a man crawling through it. A crop of sweetcorn / maize may

even hide a light tank under certain conditions. In the autumn, however, fields

were generally ploughed and visibility to ground level would have been

possible. This is impossible to model accurately without detailed contemporary

92

agricultural records that it is doubtful were kept at the time. In any case, it

would be necessary to decide a date and to estimate the height that the crop

might have grown to on that date.

When carrying out fireshed calculations with differing gun and target heights

(OFFSETA and OFFSETB values), calculations stop at the defined maximum

range examined. Bullets however do not stop here. It is improbable that a

weapon would be sited at the centre of a soup-bowl shaped patch of land,

although this is the assumption of the Advanced Method of calculating complex

firesheds above. It is a fair assumption to say that terrain would be uneven;

containing many ‘lumps and bumps’. If the gun is ranged on one of these, there

will be an overspill of fire when not pointing directly at it. The systems

developed above leave no room for the estimation of the point at which the

gunner or fire commander decided to set the sights on.

Future use of the system should take into account the actual elevations of

loopholes in pillboxes. A large proportion of pillboxes were dug in to the

surrounding ground to camouflage them to a greater extent, and to give more

protection against incoming fire. Others were sited high on embankments and

the effects of the additional elevation on the dangerous space significantly

reduced the effects of the weapon when engaging targets. In the above

calculations, loophole height was added on to the ground level based upon

standard plans. A better model would be obtained if individual spot heights

were taken using GPS or total station, or to a lesser degree of accuracy, tape

measure or rule.

Figure 63: Pillbox M1b, Wrantage, half excavated, illustrating the level to which it was buried to enhance its camouflage

93

Figure 64: Pillbox M1a, Wrantage, obscured by trees, indicating its height above the

surrounding ground

(Note anti-tank blocks in foreground. See also Figure X – MAT601, also situated at a great

height)

Fireshed techniques need to be tested by applying to a more varied selection of

weaponry – heavy and light guns, anti-aircraft guns and mortars being examples

from the Second World War, although the study of weapons from different time

periods would also benefit from this kind of analysis.

In relation to machine gun fire, future versions of the complex fireshed

procedure should be able to estimate the size of a beaten zone, and studies

should be carried out on the use of vertical restrictions (VERT1 and VERT2) to

represent the cone of fire of a machine gun.

Earl’s script, developed to automate the construction of firesheds, has room for

development in user-friendliness and interactivity with source data. At present it

cannot alter VERT values in the weapon geodatabase, forcing the user to create

multiple entries with varying values. This is not a complicated problem. The

next step for this script is the creation of a graphical user interface (GUI) and its

development as an extension to ArcGIS that can be freely downloaded by

archaeologists and historians who already have suitable source data, in order

that they can calculate their own firesheds to add insight to their research.

In indirect fire, where for example an artillery gun is engaging a target from

behind a ridge, crest clearance is critical. It may be possible to predict the areas

where crest clearance exists enabling a artillery gun to engage targets there from

a specified gun position.

94

Whilst not experimented with above, it is possible to model various scenarios to

see what effect the capture or destruction of one or more pillboxes would have

had on the viewsheds and fire sheds. This would give some indication of the

resilience of the defences. Were there to be ‘defences in depth’ with pillboxes

behind those guarding the obstacle, it would be possible to see how effectively

these might have filled the gap with fire from the rear.

Quality of View is a technique in need of development. At present, it means

little in terms of analysable data. It is foreseeable that estimations can be made

as to the best view of a target, where views from multiple points overlap.

Likewise, techniques developed by Fisher for analysis of ‘horizon viewsheds’

(coding viewsheds into four categories – 1 = visible, 2 = on local horizon, 3 =

on global horizon, 0 = invisible – 1996) is an area for further pursuit in the field

of military archaeology. In his 1996 paper, Fisher mentions how in the planning

and design of buildings, locating them off of the horizon makes them easier to

blend in with the existing infrastructure. This is also incredibly relevant to this

study in that pillboxes and other defence structures would be badly placed if

their outline was visible on the horizon (‘skylined’) by attacking troops. The

Vickers MMG emplacements on Crimson Hill are well dug into the hillside and

are prime examples of how this form of camouflage and protection was carried

out. The analysis of other sites in this way would give an insight into the

thought process that went into choosing their location.

It is strongly recommended that this work is carried further and developed more.

It would be a huge, informative addition to the English Heritage Defence

Landscapes Study (mentioned in the introductory chapter), which would assist

greatly in the understanding and interpretation of these monuments of twentieth

century warfare, and in heightening the awareness of the general public of

military sites that are commonly disregarded as uninteresting at present. The

Defence Landscape sites, which have already been selected on the Taunton

Stopline in Somerset, would be an obvious first choice as the terrain data should

be available from Somerset County Council and the knowledge of how best to

use it now exists. Moreover, there is a large and increasing amount of

information and analysis available concerning the Taunton Line defence plans,

the weapons and troops who would have manned the line from Hunt’s ongoing

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work. Moreover, the Taunton Line would be a particularly worthwhile

example, as it is considered to be one of the best preserved stop lines in the UK

(Alexander 1998). These techniques could also be applied to modern military

planning but this needs further detailed investigation.

Conclusions The relative ease in calculating firesheds and analysing defence structures, using

standard procedures built in to most modern GIS, means that any researcher can

use an off-the-shelf package to create a more in-depth picture of the

effectiveness of defence sites from any time period. The applicability of the

methodology to any projectile in motion, whether launched by an Iron Age

person or by a twentieth century soldier, makes this an invaluable tool for all

branches of archaeology. With some development, it will become easier to use

and its output will be able to show far more than is possible using the current

system.

Figure 65: Overgrown and forgotten: A pillbox on the Great Western Railway, south of Creech, originally disguised as a signal box (David Hunt)

Currently, local and national government archaeologists are beginning to realise

the importance of Second World War military sites. Although there is a growing

public interest, recent military sites are still at risk of destruction through the

more widely held public disinterest. Application of fireshed analysis by local

and national authorities will bring a great deal more to the field in way of

removing public ignorance and provoking thought, memories and intrigue.

Enabling the public to see the sites as dynamic places which played a vital role

in the protection of the country, rather than static concrete structures, overgrown

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and forgotten relics of the past, will help to preserve the memory and ignite new

interest into the archaeology of one of the tensest periods of British, and indeed

world, history. In this age when the oral testimonies of those with first hand

experience of the Second World War are beginning to disappear, it is imperative

that the remaining archaeology is not lost in the same way, and by stimulating

public interest by bringing sites alive, we can be sure this will never happen.

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Appendix I: Background to the Taunton Stopline The Taunton Stopline runs for approximately 50 miles from the mouth of River

Brue at ST300470 to the mouth of the River Axe in Devon at SY898256 (with

some infrastructure in Dorset). Some rear positions were prepared to the east of

line. It connected to the ‘GHQ Line Green’ running east along River Brue

(Somerset County Council, PRN 15450).

The line followed the River Parrett to Bridgwater where it joined the Bridgwater

to Taunton Canal (Somerset County Council, PRN 43826) at ST304362. From

Creech St Michael at ST271256 if followed the old Chard Canal (Somerset

County Council, PRN 53321) until at ST340160, southwest of Ilton it joined the

Great Western Railway (Somerset County Council, PRN 55451). The line left

the railway to the north of Chard Junction (Somerset County Council, PRN

55435) at ST338049 from where it followed the Southern Railway (Somerset

County Council, PRN 57006) and River Axe running south into Devon at

ST329028.

Figure 66: View from the top of Crimson Hill north towards Wrantage

Route of Chard Canal (also that of Stopline) marked (David Hunt)

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The planned infrastructure (most of which was built) included 233 pillboxes, 61

medium machine gun emplacements, 21 anti-tank gun emplacements, 83 road

blocks, 22 railway blocks and 46 demolitions. The anti-tank obstacle consisted

of about 24 miles of waterways, 7 miles of improved water obstacles, 11 miles

of anti-tank ditches and 8 miles of artificial obstacles (e.g. cubes).

Figure 67: Type 24 pillbox, Buckland, Somerset (Tacchi 2003)

The Type 24, in the middle distance, really stands out as there is no cover on the east bank at this stage of the canal. It covered a crossing place where a swing

bridge had been demolished in July 1940 as a Preliminary Demolition. The main Paddington to Penzance railway line runs along just behind it.

[Map ref. ST 297271] (Tacchi 2003)

From autumn 1940, twelve locations were prepared for all-round defence as

‘anti-tank islands’ of which nine were in Somerset - Bridgwater (Somerset

County Council, PRN 16380), Durston (Somerset County Council, PRN

16340), Creech St Michael (Somerset County Council, (PRN 16381), Wrantage

and Crimson Hill (Somerset County Council, PRN 16382), Ilton (Somerset

County Council, PRN 16383), Ilminster (Somerset County Council, PRN

16384), Chard (Somerset County Council, PRN 16385), Forton and Perry Street

(Somerset County Council, PRN 16386) (Adapted from Hunt Unpublished-a).

Reconnaissance for the stopline took place between the 27th and 29th June 1940

and construction was completed by November of the same year (Hunt 2003). It

was constructed, like the other stoplines in Britain, of ‘a combination of natural

and man-made anti-tank obstacles’ (Alexander 1998:9). Rivers, canals and

railways were chosen as obstacles as their banks were often steep enough to

prevent a tank climbing them. In areas where the banks were not as steep as

desired, they were scarped and built up to a level at which they were effective,

or were supplemented with concrete posts such as those in Figure 69. In areas

without banks, for instance, where the stopline crossed fields, anti-tank ditches

were excavated and anti-tank blocks were laid. Roads were fitted with grooved

concrete blocks on either side into which sections of railway line were to be

inserted to block the road. Bridges were packed with explosives to be

demolished when appropriate and mines were placed in sockets in both roads

and bridges to immobilise tanks by blowing their tracks off. Much of this

defence architecture still exists and the

Taunton stopline has been credited as one

of the best-preserved lines in the country

(Alexander, cited by Hunt Unpublished-

a). Pillboxes and road blocks, due to their

design, are not easy to demolish, and as

such, remain, overlooked and overgrown

in fields and hedgerows. Demolition has

occurred where the defences presented a

hazard to traffic, and some landowners

w

ca

so

br

th

of

m

ad

5 TEn

Figure 68: Possible mine socket in a railway bridge, Donyatt, Somerset

(£1 coin shown for scale)

99

ere paid five or ten pounds to remove pillboxes, but kept the money without

rrying out the work (Hunt 2003). Smaller, less obvious features such as mine-

ckets and now bricked-up demolition charge compartments in the supports of

idges are clearly visible to the trained eye. It was discovered on a field trip to

e area as part of the research for this study, that even the more portable parts

stopline defences are still to be found, when a length of railway track

easuring the exact length of a road block was discovered in a hedgerow

jacent to a road block site at Hammonds Farm, west of Crimson Hill.5

he section of railway track was photographed and reported to Chris Webster, Historic vironment Record Officer, Somerset County Council.

100

Figure 69: Concrete anti-tank posts added to a railway embankment, Donyatt, Somerset

Figure 70: Road blocks either side of a canal bridge, Donyatt, Somerset

(Concrete blocks slotted to accept sections of railway track)

101

Figure 71: Section of the Taunton Stopline defence plan (Crimson Hill), 1940

(Wills Collection. NMR, Swindon)

For more information on the way war affected Somerset and the way in which the county was defended, see M. Hawkins’ book, ‘Somerset at War 1939 – 1945’.

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Appendix II: Site List SMR ID NGR Designation Description Type

44647 ST 282 258 (ST 22 NE) N68 Pillbox (N68) site, Cathill Farm, Creech St Michael Pillbox

55175 ST 3136 2217 (ST 32 SW) T36 Pillbox, NE of Crimson Hill Farm, Curry Mallet Pillbox

11982 ST 3043 2796 (ST 32 NW) N62 Pillbox (N62), NW of Cogload Farm, Durston Pillbox

15904 ST 3112 2786 (ST 32 NW) T20 Pillbox (T20), W of West Lyng Pillbox

15466 ST 3089 2781 (ST 32 NW) T22 Pillbox (T22), NE of Cogload Farm, Lyng Pillbox

15042 ST 3116 2778 (ST 32 NW) T21 Pillbox (T21), S of Durston Pillbox

44322 ST 3034 2774 (ST 32 NW) NV14

Vickers machine gun pillbox (NV14), NW of Cogload Farm, Durston Vickers

44323 ST 3036 2768 (ST 32 NW) NV15

Vickers machine gun pillbox (NV15), NW of Cogload Farm, Durston Vickers

44321 ST 3037 2764 (ST 32 NW) T23 Pillbox (T23), NW of Cogload Farm, Durston Pillbox

44304 ST 2969 2708 (ST 22 NE) N63 Pillbox (N63), S of Durston Pillbox

44319 ST 2924 2689 (ST 22 NE) N64 Pillbox (N64), NE of Charlton Pillbox

44302 ST 2910 2655 (ST 22 NE) N65 Pillbox (N65), Charlton Pillbox

44300 ST 2876 2612 (ST 22 NE) N66 Pillbox (N66), SW of Charlton Pillbox

44298 ST 2848 2590 (ST 22 NE) N67 Pillbox (N67), E of Cathill Farm, Creech St Michael Pillbox

44311 ST 2706 2559 (ST 22 NE) N72 Pillbox (N72) at canal junction, Creech St Michael Pillbox

44532 ST 2746 2555 (ST 22 N70 Pillbox (N70), Creech St Michael Pillbox

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NE)

44530 ST 2731 2546 (ST 22 NE) N71 Pillbox (N71), Creech St Michael Pillbox

44287 ST 2750 2545 (ST 22 NE) T30 Pillbox (T30), E of Creech St Michael Pillbox

44338 ST 2705 2541 (ST 22 NE) N73 Pillbox (N73), N of Mill Lodge, Creech St Michael Pillbox

44288 ST 2768 2530 (ST 22 NE) T31 Pillbox, E of Creech St Michael Pillbox

44282 ST 2706 2520 (ST 22 NE) N74 Pillbox, in canal bed, S of Creech St Michael Pillbox

15886 ST 2734 2520 (ST 22 NE) T33 Pillbox (T33), S of Creech St Michael Pillbox

44289 ST 2775 2518 (ST 22 NE) T32 Pillbox, E of Creech St Michael Pillbox

15981 ST 2787 2429 (ST 22 SE) N79 Pillbox (N79), N of Thornfalcon Pillbox

44297 ST 2814 2427 (ST 22 SE) N80 Pillbox, N of Thornfalcon Pillbox

44301 ST 2887 2418 (ST 22 SE) N82 Pillbox, E of Thornfalcon Pillbox

44299 ST 2846 2411 (ST 22 SE) N81

Pillbox and AT obstacle, E of Canal Farm, Thornfalcon Pillbox

44325 ST 2951 2355 (ST 22 SE) N83 Pill box, NW of Lillesdon Court, Lillesdon Pillbox

44306 ST 2978 2346 (ST 22 SE) NV16a Pillbox, NW of Lillesdon Court, Lillesdon Vickers

44320 ST 2979 2339 (ST 22 SE) NV16b Pillbox, NW of Lillesdon Court, Lillesdon Vickers

44303 ST 2971 2332 (ST 22 SE) N84a Pillbox, NW of Lillesdon Court, Lillesdon Pillbox

44305 ST 2985 2325 (ST 22 SE) NV17a Pillbox, W of Lillesdon Court, Lillesdon Vickers

15420 ST 2989 2322 (ST 22 SE) NV17b Pillbox, W of Lillesdon Court Vickers

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15419 ST 3018 2306 (ST 32 SW) N85 Pillbox site (N85), S of Lillesdon Pillbox

44326 ST 3042 2283 (ST 32 SW) NV18 Pillbox, N of Honey Farm, Wrantage Vickers

15928 ST 3104 2283 (ST 32 SW) T40 Pillbox site, Wrantage Pillbox

44327 ST 3044 2282 (ST 32 SW) NV19 Pillbox, N of Honey Farm, Wrantage Vickers

15883 ST 3083 2280 (ST 32 SW) T41 Pillbox site (T41), N of Weaver's Farm, Wrantage Pillbox

44328 ST 3050 2278 (ST 32 SW) N86 Pill box, N of Honey Farm, Wrantage Pillbox

15884 ST 3111 2270 (ST 32 SW) T39 Pillbox (T40), Wrantage Pillbox

44329 ST 3063 2268 (ST 32 SW) MAT601

Gun emplacement, N of Higher Wrantage Farm, Wrantage AT Gun

44330 ST 3076 2252 (ST 32 SW) M1a Pillbox, N of Higher Wrantage Farm, Wrantage Pillbox

44334 ST 3121 2247 (ST 32 SW) T38 Pillbox, S of Ludwells Farm, Wrantage Pillbox

44331 ST 3084 2241 (ST 32 SW) MAT602

Gun emplacement, E of Higher Wrantage Farm, Wrantage AT Gun

44332 ST 3087 2237 (ST 32 SW) M1b Pillbox, SE of Higher Wrantage Farm, Wrantage Pillbox

55181 ST 3138 2224 (ST 32 SW) T37 Pillbox, S of Ludwell's Farm, Curry Mallet Pillbox

44333 ST 3116 2194 (ST 32 SW) M61 Pillbox, N of Crimson Hill Farm, Wrantage Pillbox

44336 ST 3130 2194 (ST 32 SW) MV1 Pillbox, NE of Crimson Hill Farm, Wrantage Vickers

44335 ST 3128 2192 (ST 32 SW) MV1a Pillbox, NE of Crimson Hill Farm, Wrantage Vickers

55179 ST 3150 2170 (ST 32 SW) MAT603

Gun emplacement, SE of Crimson Hill Farm, Curry Mallet AT Gun

55176 ST 3155 2163 (ST 32 SW) M62 Pillbox, SE of Crimson Hill Farm, Curry Mallet Pillbox

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55259 ST 3164 2153 (ST 32 SW) MAT604 Gun emplacement, W of Curry Mallet AT Gun

55180 ST 3195 2129 (ST 32 SW) M2 Pillbox, SE of Crimson Hill Farm, Curry Mallet Pillbox

99991 ST 3135 2188 M1 Missing pillbox, Crimson Hill plateau Pillbox

99992 ST 2970 2425 N84 Missing pillbox, Solomon's Hollow, Lillesdon. Type 24, Shell-proof Pillbox

44317 ST 2716 2489 Pillbox, railway embankment, E of Ruishton Pillbox

44286 ST 2716 2497 T Pillbox, on canal embankment, E of Ruishton Pillbox

44283 ST 2715 2501 Pillbox in tunnel, Ruishton, Tunnel Pillbox

44324 ST 2731 2456 Pillbox, E of Ruishton Pillbox

44318 ST 2748 2445 Pillbox, SE of Ruishton Pillbox

44281 ST 2706 2510 Pillbox, on railway, E of Ruishton Pillbox

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Appendix III: Principles of Defence (Adapted from ‘Tactical Notes for Platoon Commanders’, War Office 1941)

A Post in Concrete: Fighting from a Pillbox

(1) The concrete pillbox is a great aid to defence if intelligently used; if not,

it may become a death-trap.

(2) Concrete is a protection against bullets, shell splinters, and weather.

Sometimes it affords protection against shell fire. If properly

camouflaged, it is also a protection from ground and air observation.

(3) Many concrete posts are not complete protection against a direct hit

from a shell or from an aerial bomb. They all have the disadvantage of

limiting the field of view and the field of fire. The garrison will be

unable to use all their rifles at one and the same time because of the

fewness of the loopholes. Finally, the garrison is hindered in the

employment of the hand grenade and bayonet;

(4) Therefore the garrison of a pill box locality will act as follows:

(a) The sentry or sentries on duty will be stationed, outside the

pillbox, where they can see and hear all round them.

(b) Temporary cover from view, shell fire, and aerial bombing

maybe sought inside the pillbox; but beware that the enemy are

not creeping towards you under this covering fire, whilst you are

biding inside.

(c) When the attack comes, the light machine gun or machine gun

will fire from the pillbox, if it can carry out its task. If not, it

must come out to a prepared position.

(d) Those men who cannot use their weapons inside must man-the

trenches outside-where they can do their duty.

(e) If the pillbox is surrounded all except for those who can fire

from the loopholes, will fight outside, where they can employ all

their weapons to the best advantage.

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Scenario: The Defence of a Bridge (Applicable to the Taunton Stopline, see

Figure 72)

(1) The garrison will be astride the bridge. Posts should embrace the

roadblocks and be sited to cover all immediate approaches to the bridge.

(2) The barbed wire obstacle must be sited so that every yard of it is under

direct observation and fire.

(3) The aim of the garrison must be that no unauthorized person can

penetrate in to the perimeter of the bridge defence, i.e. the wire round it.

(4) The garrison, therefore, is disposed to safeguard the bridge against an

enemy who:

(a) may attack from any direction;

(b) may approach within assaulting distance under cover of

darkness, early morning mist, artificial smoke, or by covered

approaches;

(c) or may attempt to overcome the garrison by a ruse, i.e., by

arriving in a motorcar, or on foot, dressed as civilians or as

British soldiers.

(5) The command post will have an observation post (O.P.) from which the

maximum amount of ground immediately surrounding the bridge can be

seen. At least one sentry will be on duty throughout the hours of

daylight.

(6) All defensive posts and positions will be concealed from ground and air

observation by camouflage. Alternative positions, i.e., other positions

from where the same task can be performed, will always be constructed.

(7) Wherever possible, visual communication will be established from the

garrison on the bridge to the nearest neighbouring unit.

(8) Every bridge garrison will have signal rockets as an alarm signal that

they are being attacked.

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(9) Every bridge garrison will include at least one bicycle and one or more

orderlies who will know the best way to the nearest neighbouring unit

which can give assistance if the garrison of the bridge is in difficulties.

(10) If the garrison is larger than that required for the close defence of

the bridge, a ring of outposts may be employed.

Figure 72: Defending a bridge or crossing point (Mace 1996:4)

Scenario: Holding a River or Canal (Applicable to the Taunton Stopline)

(1) The forward garrison will be so disposed that they can cover the water

by direct observation and fire: In no circumstances will any stretch of

water be left un-guarded. The enemy will certainly cross by any such

unguarded stretch.

(2) Every post sited to guard the water will be hidden and camouflaged

from ground observation and, as far as possible, air observation as well.

(3) Alternative sites will be prepared, that is, sites from which the same task

can be performed but in a different locality. The garrison, if spotted and

shelled, can then move to a safer place and avoid casualties.

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(4) Local reserves will be so placed that they can immediately counter-

attack any enemy who have succeeded in gaining a footing on our bank.

This is their duty.

(5) At night, or during mist or fog, moving patrols must guard the gaps

between posts to ensure that the water is kept under constant

observation,

(6) When time permits, dummy' trenches of conspicuous nature will be

made to draw the enemy's fire on to places where it will not harm our

troops.

The scenarios above are applicable to the Taunton Stopline with the following

main variation: each post mentioned would, instead of being a temporary

construction, have been formed by one or more pillboxes, thus making it harder

for an attacking enemy to destroy those defending the obstacle and consequently

cross it.

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Appendix IV: German Attack Tactics German techniques of attack relied mainly upon armoured fighting vehicles.

Light and medium tanks formed the hard core of a ‘Panzer’ or armoured

division. To prepare the way ahead of them, there were armoured cars and

motorcyclist machine gunners. For close support there were batteries of field

artillery and batteries of anti-tank guns and machine guns. To occupy the

ground that the tanks had overrun, trucks and troop carriers followed close

behind, deploying infantry troops to hold the newly captured ground. Engineers

were carried to advise on crossing water obstacles, and a crew of maintenance

personnel ensured mechanical equipment and vehicles did not break down.

Communication was key and radio operators and signallers ensured all parties

were able to pass on vital information. The division also had its own aircraft, in

constant communication with the front-line troops, to provide air support to the

attack. The armoured corps as a whole was the pride of the German army and

nothing was spared in providing it with a solution to every situation.

An attack began long before the first shell was fired. A great number of

divisions was assembled in an area invisible to the defending force, then a

‘crash bombardment’ of the defences ensued, with attack coming from the air

and from artillery weapons on the ground. The leading tanks quickly followed

this up with a vigorous mass advance in which obstacles were charged through,

brushed aside or overcome in some way. Tactics were ruthless to the level that a

leading tank would be sacrificed to fill a ditch so that others could drive over it

and continue unhindered. This kamikaze nature continued into minefields – if

they were destroyed, others would know that the ground they had already

crossed was safe, and clearing the way would be much easier. Used thus, with

reckless disregard of loss, at full speed and with maximum weight, the tanks

would certainly, at one point or several, succeed in bursting through the defence

network.

This ‘break in’ was only the first phase, after which the next aim was to cripple

or destroy the defending air force before it had the chance to give warning of the

coming assault. When aircraft could not be destroyed, prolonged attacks on

aerodromes would ensure aircraft were grounded and could not retaliate. The

air, therefore, was kept clear for the dive-bomber (vulnerable to fighter aircraft,

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so only deployed at this point) to clear up any centres of anti-tank resistance that

may have survived the initial wave of attack. Immediately following dive-

bomber attack, tanks and infantry would ‘mop up’ the survivors, enabling even

the most formidable of defences to be overcome.

Immediately the first tanks had breached the defended line, infantry and faster

vehicles (motorcycles and armoured cars) would pour through the gap leaving

the slow moving tanks to clear up localised resistance. This influx of troops was

designed to thrust boldly and unhesitatingly ahead in their appointed zones of

action. Some would fan out on either side of the gap and attack the unbroken

portions of the line from the rear – a situation seldom planned for. This would

widen the opening for more reinforcements to enter. Most, however, would

thrust deeper into the newly gained land, aiming for the administrative

organisations which were largely undefended, deprived of which an army can

never fight or hold together for long. Headquarters, communications, dumps,

depots, supply and transport columns, repair shops, railways, airfields and more

were the new targets, with the aim of causing confusion amongst the defending

force. Aircraft were also re-routed to this task. Panic, confusion and congestion

were the new tactics in the field.

(Adapted from Anon 1942:88-93)

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Appendix V: Visual Basic Complex Fireshed Script By Graeme Earl Attribute VB_Name = "Module1" Option Explicit Public SCRIPTroot As String Public DBFFiles As String Public TEMPFiles As String Public RASTERFiles As String Public MAINDEM As String Public IMPERIALDataInput As String Public MaxRANGEofFIRE As Long Public FEATUREField As String Public NUMBERofFEATURES As Integer Public BarrelDepression As Single Public NUMBERBarrelIterations As Integer Public MaxBarrelAngle As Single Public BarrelIterationValue As Single Sub SetGlobals() ' set constants SCRIPTroot = "y:\" DBFFiles = SCRIPTroot & "gis\" TEMPFiles = SCRIPTroot & "Temp\" RASTERFiles = SCRIPTroot & "gis\" MAINDEM = "dem25mtrees" IMPERIALDataInput = True MaxRANGEofFIRE = 600 ' in yards for the weapon FEATUREField = "CountMe" ' the name of the field in your geodatabase with feature ID integers from 1 upwards NUMBERofFEATURES = 1 ' the number of features in your table (NB this the number of guns not every row corresponding to a barrel angle) NUMBERBarrelIterations = 9 ' the number of angle samples to produce MaxBarrelAngle = 13 ' the maximum barrel angle, in ArcGIS "VERT" notation BarrelIterationValue = 3.375 ' degrees ' NB: the Maximum and calculated barrel angles must fall within the constraints for the pill box/ weapon ' Also the values in the weapon feature table must match the above ' e.g. with number barrel it as 5 and max angle as 45 and barrelitvalue as 10, five samples will be produced at 45, 35, 25, 15 and 5 degrees ' INSTRUCTIONS ' Ensure all of the above variables are completed an correct. For example, do the directories exist ? Is the number of features ' the same as the table in the geodatabase ? Ensure that only one feature geodatabase is loaded as the script searches down

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' until it finds one and uses the first one it finds. Also ensure that the Feature field matches that specified above and that ' this field contains ALL INTEGER values between 1 and your value for NUMBERofFEATURES. ' If necessary change the bounding box values for the calculations. These use the values a few lines below. ' Finally, go to the ReclassifyRaster function and make chanes to the reclassification parametres as required. End Sub Sub IDigGuns() 'set mouse cursor to hourglass Dim pMCur As IMouseCursor Set pMCur = New MouseCursor pMCur.SetCursor 2 ' declare variables Call SetGlobals Dim inputRasterFilename As String Dim RANGEofFIRE As Integer Dim XMin As Double Dim YMin As Double Dim XMax As Double Dim YMax As Double RANGEofFIRE = MaxRANGEofFIRE If IMPERIALDataInput = False Then RANGEofFIRE = Int(RANGEofFIRE * 0.9144) End If ' **************************** These values define the analysis bounding box ************** ' default values to enclose whole study area XMin = 325800 YMin = 120700 XMax = 332200 YMax = 128200 'XMin = 331280 - RANGEofFIRE 'YMin = 121920 - RANGEofFIRE 'XMax = 331280 + RANGEofFIRE 'YMax = 121920 + RANGEofFIRE ' **************************** These values define the analysis bounding box **************

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'inputRasterFilename = "stline3" ' Loop through the table creating the rasters Dim CurrentBarrelIteration As Integer CurrentBarrelIteration = 0 Dim CurrentFeature As Integer For CurrentFeature = 1 To NUMBERofFEATURES * NUMBERBarrelIterations CurrentBarrelIteration = CurrentBarrelIteration + 1 ' Loop through the angles of barrel depression BarrelDepression = MaxBarrelAngle - ((CurrentBarrelIteration - 1) * BarrelIterationValue) ' angle of the gun Dim NewRangeRaster As IRaster Set NewRangeRaster = TheRangeRaster(RANGEofFIRE, XMin, YMin, XMax, YMax, CurrentFeature) ' open raster 'Dim OpenedRaster As IRasterDataset 'Set OpenedRaster = OpenRasterDataset(RASTERFiles, inputRasterFilename) ' perform reclassification Dim ReclassifiedRaster As IRaster Set ReclassifiedRaster = ReclassifyRaster(NewRangeRaster) ' Creates the float version and divides by 100 to create centimetres Dim FloatedRaster As IRaster Set FloatedRaster = FloatDividedRaster(ReclassifiedRaster) Dim RasterWithNoNoData As IRaster 'Set RasterWithNoNoData = RemoveNoData(FloatedRaster) Set RasterWithNoNoData = FloatedRaster Dim CutDEMRaster As IRaster Set CutDEMRaster = SubtractCone(RasterWithNoNoData) Dim VisibilityRaster As IRaster Set VisibilityRaster = GetVisibility(CutDEMRaster, CurrentFeature) ' Add raster to display - use the next 5 lines to display stages in construction 'Call AddRasterLayer(NewRangeRaster) 'Call AddRasterLayer(ReclassifiedRaster) 'Call AddRasterLayer(FloatedRaster) 'Call AddRasterLayer(RasterWithNoNoData) 'Call AddRasterLayer(CutDEMRaster) ' Add fireshed raster to display Call AddRasterLayer(VisibilityRaster)

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' reset the barrel angle loop If CurrentBarrelIteration = NUMBERBarrelIterations Then CurrentBarrelIteration = 0 End If Next CurrentFeature Set pMCur = Nothing Dim MessageString MessageString = "Done creating firesheds. Created " & NUMBERofFEATURES If NUMBERofFEATURES = 1 Then MessageString = MessageString & " fireshed for each of " & NUMBERBarrelIterations & " barrel angles" Else MessageString = MessageString & " firesheds for each of " & NUMBERBarrelIterations & " barrel angles" End If MsgBox MessageString, vbOKOnly, "IDigGuns Completed" End Sub Function TheRangeRaster(RANGEofFIRE As Variant, XMin As Double, YMin As Double, XMax As Double, YMax As Double, CurrentFeature As Integer) As IRaster ' calculate new maximum range RANGEofFIRE = ConvertRange(MaxRANGEofFIRE, 0, BarrelDepression, True) 'On Error GoTo ERH: ' Get the Map Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pMap As IMap Set pMap = pMxDoc.FocusMap ' Get the input source data from the first layer in ArcMap Dim pGeoDs As IGeoDataset Dim pLy As ILayer Dim ThisLayer As Integer ' counter for looping through layers Dim NoFeatures As Boolean ' checks whether the feature has been found NoFeatures = False For ThisLayer = 1 To (pMap.LayerCount) Set pLy = pMap.Layer(ThisLayer - 1)

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' if the feature layer is found then use it If TypeOf pLy Is IFeatureLayer Then NoFeatures = False Exit For Else NoFeatures = True End If Next ThisLayer If NoFeatures = True Then MsgBox "The appropriate feature layer must be loaded." Exit Function End If Dim pFeatureLy As IFeatureLayer Set pFeatureLy = pLy Set pGeoDs = pFeatureLy.FeatureClass Dim CurrentID As Integer Dim CurrentField As String CurrentID = CurrentFeature CurrentField = FEATUREField Dim CurrentPoint As IFeatureClassDescriptor Dim sFieldName As String Dim pQueryFilter As IQueryFilter Set pQueryFilter = New QueryFilter ' Set the where clause pQueryFilter.WhereClause = CurrentField & " = " & CurrentID sFieldName = CurrentField Set CurrentPoint = New FeatureClassDescriptor CurrentPoint.Create pGeoDs, pQueryFilter, sFieldName ' Create a Distance operator Dim pDist As IDistanceOp Set pDist = New RasterDistanceOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pDist Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Set output extent and cell size Dim pExt As IEnvelope Set pExt = New Envelope pExt.XMin = XMin pExt.YMin = YMin pExt.XMax = XMax pExt.YMax = YMax

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pEnv.SetExtent esriRasterEnvValue, pExt Dim CellRes As Variant CellRes = 10 pEnv.SetCellSize esriRasterEnvValue, CellRes ' Perform the Euclidean distance Path Dim pRangeOutRaster As IRaster Set pRangeOutRaster = pDist.EucDistance(CurrentPoint, RANGEofFIRE) ' Add it into ArcMap ' Dim pRLayer1 As IRasterLayer ' Set pRLayer1 = New RasterLayer ' pRLayer1.CreateFromRaster pRangeOutRaster ' pMap.AddLayer pRLayer1 Set TheRangeRaster = pRangeOutRaster 'ERH: ' MsgBox "gone wrong: " & Err.Description ' Exit Sub End Function Function ReclassifyRaster(pInputDataset As IRaster) As IRaster 'On Error GoTo ERH ' Create the RasterReclassOp object Dim pReclassOp As IReclassOp Set pReclassOp = New RasterReclassOp ' Open a remap table using the OpenTableFromDBFFile function below 'Dim pRemapTable As ITable 'Set pRemapTable = OpenTableFromDBFFile(DBFFiles, "RemapTable2.dbf") Dim RasterToReclass As IRaster Set RasterToReclass = pInputDataset ' Set the Remap using the number remap method Dim pRemap As IRemap Dim pNRemap As INumberRemap Set pNRemap = New NumberRemap 'pNRemap.LoadNumbersFromTable pRemapTable, "Out", "From", "To", "Mapping" Dim Ranges(12) As Long ' range end points Dim Elevations(12) As Single ' heights at sample points on curve Dim DivisionsPerRange As Single ' number of divisions Dim Samples As Integer ' number of range samples

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Dim ImperialInput As Boolean ' whether input data is in imperial (default) Dim OutputElevation As Integer ' the output elevation Ranges(0) = 0 Elevations(0) = 0 ' *********** complete the ranges and elevations arrays ******* Ranges(1) = 100 Ranges(2) = 200 Ranges(3) = 300 Ranges(4) = 400 Ranges(5) = 500 Ranges(6) = 600 Elevations(1) = 1.85 Elevations(2) = 3.7 Elevations(3) = 4.4 Elevations(4) = 4.1 Elevations(5) = 2.6 Elevations(6) = 0 ' Enter the number of samples. Do NOT include the first zero value but do include the final zero value ' The final zero value should also be entered in the two arrays e.g. Ranges(11)= 1100 Elevations(11) = 0 ' If you have less than the above arrays you can ignore the array slots after the SAMPLES value ' The number of samples INCLUDES the first and last zeros Samples = 6 DivisionsPerRange = 5 ' Convert ranges and elevations to cope with rotated trajectory. In the words of MC Hammer - can't touch this Dim LoopThroughArray As Integer For LoopThroughArray = 1 To Samples - 1 Ranges(LoopThroughArray) = ConvertRange(Ranges(LoopThroughArray), Elevations(LoopThroughArray), BarrelDepression, True) Elevations(LoopThroughArray) = ConvertRange(Ranges(LoopThroughArray), Elevations(LoopThroughArray), BarrelDepression, False) Next ImperialInput = IMPERIALDataInput ' *********** complete the ranges and elevations arrays *******

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' *************** Do not change anything below here *********** Dim RangeLength As Integer Dim ThisDivisionDifference As Single Dim ThisElevationDifference As Single Dim NumberOfSamples As Integer Dim NumberOfDivisions As Integer Dim LastButOneDivision As Integer Dim CurrentRangeValue As Single Dim CurrentElevationValue As Single Dim CurrentElevation As Single Dim PreviousRange As Single PreviousRange = 0 Dim OutputString As String ' Loop through the ranges calculating the inter-range difference, stopping at the penultimate sample For NumberOfSamples = 0 To (Samples - 2) RangeLength = Ranges(NumberOfSamples + 1) - Ranges(NumberOfSamples) ' Calculate the length difference of each successive new division ThisDivisionDifference = RangeLength / DivisionsPerRange ' Calculate the elevation difference for each of these divisions ThisElevationDifference = (Elevations(NumberOfSamples + 1) - Elevations(NumberOfSamples)) / DivisionsPerRange ' Finds the start of the last division and loops through this many times adding Values LastButOneDivision = Fix(DivisionsPerRange) For NumberOfDivisions = 1 To LastButOneDivision ' Multiply the position in the sequence by the difference per division If NumberOfDivisions = 1 Then ' Check for the first value CurrentRangeValue = 0 + Ranges(NumberOfSamples) Else CurrentRangeValue = ((NumberOfDivisions - 1) * (ThisDivisionDifference)) + Ranges(NumberOfSamples) End If If NumberOfDivisions = 1 Then ' Check for the first value CurrentElevationValue = 0 + Elevations(NumberOfSamples) Else CurrentElevationValue = ((NumberOfDivisions - 1) * (ThisElevationDifference)) + Elevations(NumberOfSamples) End If If ImperialInput = True Then CurrentElevationValue = CurrentElevationValue * 0.3048 CurrentRangeValue = CurrentRangeValue * 0.9144 End If

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CurrentElevationValue = CurrentElevationValue * 100 OutputElevation = CurrentElevationValue 'OutputString = OutputString & "Range: " & PreviousRange & "-" & CurrentRangeValue & ", Elevation: " & OutputElevation & "END" ' ********************** output range value ***************** pNRemap.MapRange PreviousRange, CurrentRangeValue, OutputElevation ' ********************** output range value ***************** PreviousRange = CurrentRangeValue Next Next ' Add the last line pNRemap.MapRange PreviousRange, Ranges(Samples - 1), 0 'OutputString = OutputString & "Range: " & PreviousRange & "-" & Ranges(Samples - 1) & ", Elevation: 0END" Set pRemap = pNRemap 'Set ReclassifyRaster = pReclassOp.Reclass(RasterToReclass, pRemapTable, "From", "To", "Out", True) Set ReclassifyRaster = pReclassOp.ReclassByRemap(RasterToReclass, pRemap, True) 'Set ReclassifyRaster = RasterToReclass Erh: 'MsgBox "Failed to Perform reclassification." & Err.Description & Err.Number End Function Function FloatDividedRaster(RasterToFloat As IRaster) As IRaster ' Get the Map 'Dim pMxDoc As IMxDocument 'Set pMxDoc = ThisDocument 'Dim pMap As IMap 'Set pMap = pMxDoc.FocusMap ' Get the input raster from the first layer in ArcMap 'Dim pLayer As ILayer 'Set pLayer = pMap.Layer(0) 'If Not TypeOf pLayer Is IRasterLayer Then ' Exit Function

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'End If 'Dim pRLayer As IRasterLayer 'Set pRLayer = pLayer Dim pInRaster As IRaster Set pInRaster = RasterToFloat ' Create a Spatial operator Dim pAlgbOp As IMapAlgebraOp Set pAlgbOp = New RasterMapAlgebraOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pAlgbOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Bind a raster Call pAlgbOp.BindRaster(pInRaster, "R1") ' Perform Spatial operation Set FloatDividedRaster = pAlgbOp.Execute("Float ([R1]) / 100") End Function Public Function OpenRasterDataset(sPath As String, sFileName As String) As IRasterDataset ' Returns RasterDataset object given a file name and its directory ' sPath: path of the input raster dataset ' sFileName: name of the input raster dataset On Error GoTo Erh Dim pWSFact As IWorkspaceFactory Dim pRasterWS As IRasterWorkspace Set pWSFact = New RasterWorkspaceFactory If pWSFact.IsWorkspace(sPath) Then Set pRasterWS = pWSFact.OpenFromFile(sPath, 0) Set OpenRasterDataset = pRasterWS.OpenRasterDataset(sFileName) End If Exit Function Erh: Set OpenRasterDataset = Nothing MsgBox "Failed in Opening RasterDataset. " & Err.Description End Function Public Sub AddRasterLayer(pRaster As IRaster) On Error GoTo Erh ' Adds a layer to an ArcMap session Dim pRasterLayer As IRasterLayer

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Set pRasterLayer = New RasterLayer pRasterLayer.CreateFromRaster pRaster Dim pMap As IBasicMap Dim pMxDoc As IMxDocument Dim pActView As IActiveView Set pMxDoc = ThisDocument Set pMap = pMxDoc.FocusMap Set pActView = pMxDoc.ActiveView pMap.AddLayer pRasterLayer pActView.Refresh pMxDoc.UpdateContents Exit Sub Erh: MsgBox "Failed to Add Raster Layer." & Err.Description End Sub Function SubtractCone(coneRaster As IRaster) As IRaster ' takes in trajectory cone and subtracts it from the DEM ' Open DEM ' open raster Dim OpenedDEM As IRasterDataset Set OpenedDEM = OpenRasterDataset(RASTERFiles, MAINDEM) Dim ConvertedRaster As IRaster Set ConvertedRaster = OpenedDEM.CreateDefaultRaster ' Create a Spatial operator Dim pMathOp As IMathOp Set pMathOp = New RasterMathOps ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pMathOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Perform the operation Set SubtractCone = pMathOp.Minus(ConvertedRaster, coneRaster) End Function Function GetVisibility(InputDEMSurface As IGeoDataset, CurrentFeature As Integer) As IRaster ' Get the Map Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pMap As IMap Set pMap = pMxDoc.FocusMap

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' Get the input source data from the first layer in ArcMap Dim pGeoDs As IGeoDataset Dim pLy As ILayer Dim ThisLayer As Integer ' counter for looping through layers Dim NoFeatures As Boolean ' checks whether the feature has been found NoFeatures = False For ThisLayer = 1 To (pMap.LayerCount) Set pLy = pMap.Layer(ThisLayer - 1) ' if the feature layer is found then use it If TypeOf pLy Is IFeatureLayer Then NoFeatures = False Exit For Else NoFeatures = True End If Next ThisLayer If NoFeatures = True Then MsgBox "The appropriate feature layer must be loaded." Exit Function End If Dim pFeatureLy As IFeatureLayer Set pFeatureLy = pLy Set pGeoDs = pFeatureLy.FeatureClass Dim CurrentID As Integer Dim CurrentField As String CurrentID = CurrentFeature CurrentField = FEATUREField Dim CurrentPoint As IFeatureClassDescriptor Dim sFieldName As String Dim pQueryFilter As IQueryFilter Set pQueryFilter = New QueryFilter ' Set the where clause pQueryFilter.WhereClause = CurrentField & " = " & CurrentID sFieldName = CurrentField Set CurrentPoint = New FeatureClassDescriptor CurrentPoint.Create pGeoDs, pQueryFilter, sFieldName ' Create the RasterSurfaceOp object Dim pSurfaceOp As ISurfaceOp Set pSurfaceOp = New RasterSurfaceOp ' Declare the input raster object Dim pElevation As IGeoDataset

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' Calls function to open a raster dataset from disk 'Set pElevation = OpenRasterDataset(RASTERFiles, MAINDEM) Set pElevation = InputDEMSurface ' Declare the input feature class object Dim pObservers As IGeoDataset ' Calls function to open a points dataset from disk 'Set pObservers = OpenFeatureClassDataset("D:\SpatialData", "observers") Set pObservers = CurrentPoint ' Declare the output raster object Dim pOutputRaster As IGeoDataset ' Calls the method Set GetVisibility = pSurfaceOp.Visibility(pElevation, pObservers, esriGeoAnalysisVisibilityFrequency) End Function Function RemoveNoData(InputRaster As IRaster) As IRaster 'On Error GoTo Err: ' Create a Spatial operator Dim pAlgbOp As IMapAlgebraOp Set pAlgbOp = New RasterMapAlgebraOp ' Set output workspace Dim pEnv As IRasterAnalysisEnvironment Set pEnv = pAlgbOp Dim pWS As IWorkspace Dim pWSF As IWorkspaceFactory Set pWSF = New RasterWorkspaceFactory Set pWS = pWSF.OpenFromFile(TEMPFiles, 0) Set pEnv.OutWorkspace = pWS ' Bind a raster Call pAlgbOp.BindRaster(InputRaster, "R1") ' Perform Spatial operation Set RemoveNoData = pAlgbOp.Execute("con(isnull ([R1]), 0, [R1])") 'Set RemoveNoData = InputRaster 'Err: 'MsgBox "buggered up again: " & Err.Description 'Exit Function End Function Function OpenTableFromDBFFile(dbfPath As String, dbfFile As String) As ITable Dim pMxDoc As IMxDocument Set pMxDoc = ThisDocument Dim pWorkspace As IWorkspace

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Dim pFact As IWorkspaceFactory Set pFact = New ShapefileWorkspaceFactory Set pWorkspace = pFact.OpenFromFile(dbfPath, 0) Dim pFWorkspace As IFeatureWorkspace Set pFWorkspace = pWorkspace Set OpenTableFromDBFFile = pFWorkspace.OpenTable(dbfFile) End Function Function ConvertRange(InputXValue As Long, InputYValue As Single, InputAngle As Single, OutputTheX As Boolean) As Single Dim OutputAngle As Single ' convert to angles the radial angle calulator understands OutputAngle = (InputAngle * -1) + 90 Dim AngleFromZero As Double Dim RotationAboutOrigin As Single Dim TrajHypotenuse As Double Dim pi As Double Dim NewX As Double Dim NewY As Double pi = 3.14159265358979 TrajHypotenuse = Sqr((InputXValue * InputXValue) + (InputYValue * InputYValue)) AngleFromZero = (Atn(InputYValue / InputXValue)) * (180 / pi) RotationAboutOrigin = OutputAngle - AngleFromZero NewX = TrajHypotenuse * Sin((RotationAboutOrigin) * (pi / 180)) NewY = TrajHypotenuse * Cos((RotationAboutOrigin) * (pi / 180)) If OutputTheX = True Then ConvertRange = NewX Else ConvertRange = NewY End If End Function

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