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Corps) to which a drawing section of 514 Field Survey Company R.E. was attached.
These block plots were specially prepared for the El Alamein battle and were used successfully by the counter-battery organization for concentrating artillery fire on to enemy gun positions and defence works before and during the battle.7 The lack of sufficient aircraft to do the survey part of the work well in advance meant that the vertical survey photographs had to be obtained during the last few difficult weeks in face of heavy enemy opposition.8
The importance of block plots and their value to the Eighth Army may be judged from the fact that the first Mosquito aircraft supplied to the Desert Air Force were, at the personal request of General Montgomery, used by 60 Squadron (S.A.A.F.) for aerial survey work.9
The practical use of the block plot principle involved the preparation of a set of overlapping photographs, each having its principal point, and those of adjacent photos, marked on it. Accompanying the photos was a gridded map, or plain piece of gridded paper, on which the principal points were plotted. Using a piece of transparent talc or kodatrace, any target which could be recognized on two overlapping photos could be cut in on the plot-sheet or gridded map, and its position fixed on the radial line principle. It was of special use in areas where there was little map detail.10
The Campaign in Sicily
There is no mention by Brigadier Clough of the use of block plots during the invasion and battle for Sicily but the war diary for 517 Field Survey Company RE on the 1st July 1943 (24) mentions instructions being received for 7 General Survey Section to do block plots of Sicily.
1st July 1943
Instructions for 7 Gen Svy Sec to do block plots of Sicily.11 The Italian Campaign
Their modified use in the Italian campaign is however recorded in some detail: -
Arrival of 30 Engineer Topographical Battalion (U.S.)
This unit with its extensive mapping resources including multiplex equipment, became available for work at A.F.H.Q. during February 1944, and was employed without delay on the following types of work: -
Improvement and revision of 1/50,000 maps of Italy.
Collation maps of Italy (1/50,000).
Block-plots in Fifth Army area
Revision and improvement of 1/25,000 maps of eastern France.
Town plans in southern France.
A.F.H.Q. was asked to prepared block-plots covering areas in advance of the Fifth Army front where there was little trig control, and where the available photos had excessive tilts. The photo-centres were located by multiplex methods to facilitate radial line plotting, and the multiplex equipment was also used to bridge the gaps between available control.12
The programme (of block plots) was a continuous one, each move forward introducing a new set of targets whose positions were required by the Counter-Battery Organization so that concentrated artillery fire could be directed on to them if required. During static periods a dense system of such targets was established on the enemy front.
Between May and September 1944, over 1,200 such fixations were determined. This target fixation work came to an end in April 1945, when the enemy forces had been defeated and were retreating.
Ground checks on 42 targets fixed on the Senio front showed that the mean point of impact of shells was on the target in 25 instances, and in only three cases was it more than 50 yards off. Assuming perfect gunnery this represented a very satisfactory result.13
Preparations for the spring offensive (1945) in Italy
No. 7 General Survey Section R.E. was attached to the Mediterranean Air Intelligence Unit (M.A.I.U. West) for several months. Its principal tasks were the fixation of targets for the counter-battery organization (C.B.O.), a check of the plotting of the Italian trig points on the
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