Page 74 - Ranger Demo

discussed; that is, adjusted base line plots on transparencies of blocks of vertical photography taken to survey specifications. I participated in their construction and use in the Western Desert campaigns in Egypt and Libya and I believe that they were also used in the Italian campaign and probably in Europe. Certain others were prepared for the possible German advance into Egypt by the “back door” in case the Russians were unable to prevent them breaking through the Caucasus.
The method of using block plots was simple and effective. Our photo-reconnaissance squadrons would fly periodic sorties over the enemy occupied part of the battle area. The vertical photographic cover was immediately processed, printed and interpreted for likely targets, such as troop concentrations, gun positions and so on. The newly interpreted targets would be hastily transferred, by inspection from adjacent detail, on to the basic photographic cover from which the block plots had been made, intersected on the block plots and their co-ordinates delivered to the gunners. As you can imagine, speed was the essence and it was not unusual for our artillery to be firing at new enemy targets within one hour of the return of a photo-reconnaissance sortie.
In the early days of the Western Desert campaigns the photo-reconnaissance survey squadrons were equipped with Maryland bombers and suffered heavy casualties at the hands of enemy fighters. Just before the battle of El Alamein, the first Mosquito squadron arrived, and these aircraft proved highly successful as they could outpace the opposing fighters. Our “Block Plottery” went on apace, thanks to the “Mossie”!29
Colonel Rogers’ recollection may be slightly in error. It is believed that the Mosquito was not used for Survey purposes until the Battle of the Mareth Line in Tunisia mid-1943.
It is almost certain that there must have been wartime Technical Instructions on the methods or procedures for the construction of Block Plots but nothing comprehensive has come to light in research so far other than a HQ ALFSEA Technical Note, No. 5, on the orientation of photography for use in Block Plots and an addendum to it on the method of recording or booking values.30 & 31
Military Use After the War
It is possible that the block plot was adopted for use in the United States forces and used in Korea but there was no British Survey participation in that war. Thereafter few campaigns have seen the use of artillery on the scale of the Second World War until Vietnam, again, another war in which there was no British Survey involvement. As already mentioned, the use of the block plot was, in 1956, still deserving of mention in the Survey Staff Manual: -
7. Air surveys. – These are surveys made from air photographs and are usually required for the preparation or revision of medium and large-scale maps.
Air photographs are also required for: -
(a) Preparation of block plots for target fixation by the RA.
(b) Studies of particular areas by photogrammetric methods.
(c) Preparation of mosaics, photomaps and gridded photographs.32
Even as late as about 1976 a modified form of the concept was still alive. At that time Lt Col C.N. Thompson, the Commanding Officer of 42 Survey Engineer Regiment was trialling the use of the Zeiss Stereotope with blocks of adjusted air survey photography as a basis for deriving co-ordinates of targets identified on reconnaissance photography taken over the same area as the adjusted block.
The Directorates of Colonial and Overseas Surveys
After the war, the depiction of principal points on topographic mapping became a standard practice in the Directorates of Colonial/Overseas Surveys under Hotine in its programme of medium-scale topographic mapping of large areas of the Commonwealth: -
The standard mapping scale of the Directorate is 1:50,000, each sheet covering 15 minutes of latitude by 15 minutes of longitude, with larger scales over small and special areas, whilst the detail is reduced to 1:100,000 or 1:125,000 where the amount of topographical detail does not justify a scale of 1:50,000.
Each map has marked on it the principal points and numbers of all the air photography used in its compilation which makes it generally suitable, in conjunction with the
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