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A brief history of British mapping in the Great War
Peter Chasseaud wrote a very comprehensive history of British survey and mapping on the Western Front entitled Artillery's Astrologers. His opening sentence states that "It is a considerable irony that France, which led the world in the 18th Century with the first scientifically based national survey, should by 1914 be one of the worst-mapped countries in Europe. It is no surprise to find that the mapping problem faced by the British Army in 1914 was very acute". Inevitably this is a complex narrative, one better suited to a more comprehensive treatment as found in his excellent book, however, a few points are useful here.
The war was not expected to be one of near static trenches, the British army was trained and equipped for wars of movement. There had been little planning for large scale detailed maps of the possible European theatre, the expected war of movement required small scale maps that can be used to show transport routes, water sources, rivers, mountains etc. not farms, hamlets, and tracks. Had there been such planning, the scope of the undertaking would have been huge.
France and Belgium did indeed have some accurate & detailed 1:20,000 maps that covered much of what became the British front, the Plan Directeur series drawn using the Lambert projection, but these were not initially used effectively except for the British area of the Aisne battlefield in 1914. That was the only part of their front mapped by the new French Topographical Survey at a scale of 1:50,000, almost all ranges and bearings for the artillery were obtained from these maps, but it was some time before that was possible elsewhere. Until late in 1915 the British muddled on with maps redrawn or based mainly on the French and Belgian 1:80,000 maps that were themselves based on a 1:40,000 survey, many drawn in the previous century. Sadly these maps were not accurate, especially the 1:80,000 sheets; they were monochrome, very hard to read and almost useless when early in the war the trench lines were established.
In the History of the Ordnance Survey, edited by WA Seymour & published by William Dawson & Sons is the passage
"The first provision of larger-scale mapping, mainly for use by the artillery, was made by the Ordnance Survey after the Battle of the Aisne in 1914. This was primarily done by enlargement from the French 1:80,000 to the scale of 1:40,000 which was the general administrative scale in trench warfare, or to 1:20,000, for the artillery and infantry alike. Colours were added to the photographic enlargements to distinguish roads, water and contours. The second edition was redrawn, but all the distortions and inaccuracies of the original map remained and it was all but useless for the artillery, creating the need for new field surveys. Southampton was also involved in the preparation of the larger-scale 1:10,000 maps from 1915 onwards. The work of reproducing these compilation maps was extremely laborious and was done partly by the Service Geographique and partly by the Ordnance Survey. The basic maps of all scales were reproduced in a variety of forms to depict specialized information such as traffic, roads and bridges, railways, enemy order of battle, water supply, hostile battery positions and geology."
To quote the official History of the Great War, by J.E. Edmonds,
" with the uncorrected maps [French 1:80000] then at the disposal of the British Force, a commander might well hesitate before involving his columns, with the enemy on their heels, in so large and blind a mass of trees."
The best that could be done was to redraw 1:40,000 and then 1:10,000 maps using these old sheets as a source of the planimetry, there not being the time to re-survey the whole area immediately. This resulted in maps that were easier to read but very inaccurate. See page on Trench Map accuracy comparison. Early British maps made this way often show errors of 150 yards or a lot more, most notably around the Loos area right up to the Battle of Loos in September 1915. In recognition of the problem, many early maps showing trenches were known to the British as trench diagrams or sketches.
From the outset, the British worked to rectify this serious situation, work that included a resurvey of their area of operations. This a huge task in itself but one undertaken in a time of war was a great deal harder as covering the enemy territory was denied except by techniques improved later such as aerial survey. A high quality peacetime survey first requires a set of very accurately placed points established by repeated triangulation from a base line- a Geodetic Survey. To gauge the scale of this task, the Principal Triangulation of Britain published in 1858 had taken 70 years to complete, not the map of Britain, just the chain of triangulation stations. Such a task to cover the Western Front would in normal circumstances have been one that occupied several years but that time was not available, instead use was made of French and Belgian Geodetic triangulation data but these data were also found to have significant errors.
The serious nature of the lack of adequate maps became even more obvious when it became known the Germans had the ability to direct artillery fire from aircraft. In response, the War Office set up experiments on Salisbury Plain in October 1914 to fix the position of an aircraft when it signalled, using a theodolite. By November 1914 this method had been superseded by using wireless.
In volume III of the History of the Great War, Edmonds wrote
" the positions of most heavy and siege batteries had been fixed by survey, and the maps and bearings of all prominent points in the German area accurately ascertained ... by the Ranging Section RE, under Captain Winterbotham, working under Major E. M. Jack of the Topographical Section, General Staff.''
As a result,, Captain Winterbotham was dubbed 'The Astrologer' after his astonishing skills as a surveyor with the gunners. Under his command, the 1st Ranging and Survey Section set out to draw an entirely new 1:20,000 map based on a new survey. In one month the Section covered the whole of the British front from Ypres to Bethune using Plane Table surveying, a technique known to the Romans centuries before. The 1: 20 000 map became seen as the ideal trench map but one also suitable for artillery. Their results, although good, were not up the the standards achieved later in the war.
The first British 1:10,000 trench map, sheet 57D SE4, became available in October 1915, not entirely from a new survey. Use was made of French cadastral (property) plans and aerial photographs. Such photography was first carried out by the Royal Flying Corps on 13 September 1914, but they had much to learn. It was after all only 11 years after the Wright Brothers first flew at Kitty Hawk.
The early unreliability of flash-spotting and sound-ranging was overcome to become the most important methods of counter-battery artillery. Both these methods of locating enemy guns rely on a very accurate map. In November 1917, Brigadier-General H. H. Tudor, CO of 9th Division Artillery, suggested that gun-laying should rely completely on survey methods instead of using the tried and tested preliminary registration fire, a method better seen as trial and error, but this method alerted the enemy to a coming action. As a result, unregistered shooting or 'predicted fire' was used to good effect at the Battle of Cambrai, the basis of this is shooting off the map or Artillery Board. The Ordnance Survey did not only supply maps, they also made available over 11,000 such boards. These consisted of a zinc-covered wooden board, on which a map or gridded sheet was fixed so that bearing and distance to a target could be established very quickly.
To add to the problems, the map projection used by both countries (Bonne) was not the best for artillery but in the circumstances, it had to be used. The British took the Belgian 1:40,000 series Bonne maps, laid them out on a large floor and extended the grid lines across France. The Belgian sheet numbering was also retained and extended into France by adding letters then fresh maps were prepared in this projection to a scale of 1:40,000. Here the British made an unfortunate error, the source maps were metric but it was assumed that a yard based system was needed by the artillery as their ballistic tables were in yards. The result was a yard based grid imposed on the metric mapping which resulted in a very poor fit. It would have been easier and quicker to redraft the artillery tables into metres and to use completely metric mapping.
The resulting 1:40,000 maps were then subdivided and re-drawn in 1:10,000, a scale best suited to infantry in the trenches and 1:20,000, the scale favoured by field artillery units. The 1:40,000 maps being better suited to heavy artillery batteries.
Pre-war efforts to produce small scale maps of 1:100,000 and 1:250,000 were in place by 1914 and good quality sheets of those scales were available but of little use in the trenches being better suited to tactical or strategic planning. It was not until late in 1915 that the British army and the Geographical Section General Staff, the GSGS, were able to effect real improvements in mapping the front. Not all trench maps were drawn to a GSGS series, a good number were produced by various Royal Engineers Field Service Companies. In the collection these are listed simply as "FSC" rather than by individual unit numbers.
What does it mean for a map to be accurate and why is it important? It is said that the Great War was a war of artillery and this is where geometrical accuracy is important. Most artillery batteries could not see their target directly, use being made of ground cover etc. to hide their position from the enemy. This means the orientation of the guns must be carried out by means not dependant on seeing the target through the gun sight, instead accurately surveyed pickets were set out for this purpose. This indirect technique requires an accurate map; if the scale is 1:20,000, a 1mm error on the map means a 20 metre error on the ground so attempts were made to achieve better than 1mm positional errors on the map. A separate problem arises when shooting off the map. The Bonne projection is one that preserves area not bearing, so bearings measured off the map are not best suited to artillery. Later in the war plans were put in place to convert to the better Lambert projection which does preserve bearing but those plans were made too late to come into effect.
Maps produced early in the war were prepared and printed by the Ordnance Survey in Southampton. This means the intelligence to update a map had to be sent to Southampton, new drawings made and new printing plates prepared. Production could then proceed but then the finished batch had to be shipped back to the front. This usually meant that the most up to date maps at the front were at least a week out of date. Later in the war a branch of the Ordnance Survey was established in France and called the OSO, Ordnance Survey Overseas. Maps printed by them are marked OSO. This allowed for maps that were more up to date but at the risk of the OSO being overrun in the event of a German breakthrough. The printing presses used at the time were very heavy and difficult to move so Southampton remained crucial throughout the war. By 1918, at least 32 million maps had been produced, an absolutely astonishing output. From 4th August 1914 to 11th November 1918 is 1560 days making the production average over 20,500 maps per day, a magnificent achievement.
To offset some of these problems, a number of smaller presses were located nearer to the fighting, these were used to produce smaller sheets in limited quantities. In addition, a number of soldiers made maps by hand, either by tracing the main detail from printed maps or by using their field skills directly.
In 1917 an Overseas Branch of the Ordnance Survey (OBOS) was established in France, at Wardrecques, near St Omer and later at Aubengue near Boulogne. Their output was enormous, on 27 March 1918 six printing machines were worked continuously and produced over 300 000 maps by the beginning of April. From 7 to 17 August, four machines printed over 400 000 maps. After 11 November 1918, they continued to print, this time covering Germany.
Most maps were printed using lithography. In its strictest form, the word lithography means printing from stone, (Ancient Greek lithos = 'stone', and graphein = 'to write') but in general language, lithography refers to printing based on the fact that oil based inks are immiscible with water. Features to be printed are marked on zinc, aluminium or other suitable surface and those features made to "accept " oil based inks, the rest of the surface cleaned with water does not. When paper is pressed hard against the surface some ink adheres from the inked features.
Using traditional lithography, marks have to be drawn in reverse, even the text. This is a slow process that takes considerable skill. Later printing machines used offset lithography whereby an intermediate rubber roller took an image from a map drawn normally, this transient image was then in reverse. The roller was then used to transfer the image to the paper. During the war great use was made of techniques based on zinc in place of the original stone using images transferred photographically. This was a great deal faster and more convenient. A lithographic stone could be 75mm thick or more and larger than the map required so it weighed a great deal and was hard to handle and store. Zinc plates were far lighter and easier to store. This photographic technique was often used to produce 1:10,000 maps from 1:20,000 base maps and vice versa, a significant saving in time and effort.
All the trench maps were produced in several print runs, first the basic mapping topography detail was printed as a base map and an edition number assigned to it. Later, in much smaller print runs, trenches, batteries, camps etc. were over printed in colour, one run through a press per colour. For this reason, when time was short there was much pressure to adopt monochrome maps. Some trench maps have a monochrome base map, some are multi-colour to show rivers etc. in blue. Nearly all overprints are in two or more colours, blue British trenches and red German trenches although later in the war these colours were reversed to reflect the French colour scheme. A base map edition once overprinted had a letter added to the edition number, so Edition 2A and 2B are the same base map with different overprint dates, usually but not always with a "trenches corrected to" date added.
By the end of the war, the combined effort had produced over 32 million maps. From the Assassination of Archduke Franz Ferdinand to Armistice day was just 1597 days. An absolutely stunning achievement for the Artillery's Astrologers.
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