Page 69 - Ranger Demo

The Western Desert & Alamein
The Block Plot was probably first used operationally during the build up to the Battle of El Alamein: -
The enemy was building up enormous strength in defences and gun positions, and it was important that our artillery should hammer these and endeavour to knock them out before our forces were committed to the assault. To effect this, it was vital that the co-ordinate positions of the enemy guns and defences should be determined with reference to the surveyed positions of our own guns, so that the guns could be laid accurately on to their targets. The Artillery counter-battery officers were asking for these co-ordinates with urgency. The block-plot was compiled by drawing the map grid on a large scale, and on this grid were plotted the principal points (or centres) of the photographs which covered the area in the form of strips of overlapping photographs. Having located on newly taken reconnaissance photographs the positions of the enemy guns and defence works, their positions with reference to the map grid were determined on the block-plot by a process of graphical intersections from the principal points of the photographs already plotted on the grid. The use of these block-plots met with very great success and was undoubtedly a great aid to the effective artillery preparations for the battle itself. Between 27th October and 2nd November, 215 new enemy gun positions were located, and a very large proportion of these were destroyed. 4
For artillery purposes, the accuracy claimed for the system was perfectly acceptable: -
A special edition of three 1/25,000 sheets showing enemy defences in the area lying south- west of Tel-el-Eisa. The defences had been located on photographs taken with a 36-inch lens and were positioned on the block-plots which covered the whole front. The positional accuracy of the detail was reckoned to be about plus/minus 20 metres.5
Brigadier Clough’s source for Block Plots was probably the periodic Middle East Survey Reports: -
An important feature of the Survey in the El Alamein battle was the Air Survey Counter Battery Plot. In its simplest form this may be described as a grid with the Principle Points of survey photographs covering the area plotted in their correct relation to the Trig. The positions of new targets appearing on the many daily recce photos were transferred to the Survey photos, and thence the co-ordinates were determined by intersection on the Plot. In practice, owing to lack of Survey aircraft to do the work in advance of the requirement, the Survey photo cover was built up be degrees over two months in the face of the enemy. The result was a patchwork of improper and mainly tilted photographs, which led to many technical Survey complications and embarrassments. Nevertheless, the results were consistently good, and in the set of circumstances occurring in this battle the Gunners found this method a most valuable source of C.B. information. An accuracy of plus or minus 50 metres was generally attained, though variations above and below this average were considerable, as might be expected from such indifferent photographs.
Between 27 October and 2 November, 215 new enemy gun positions were located. The average time from taking the photo in the air to the delivery of co-ordinates was 12 hours, only a few minutes of which was normally occupied in the Survey plotting.
This method is of great importance in areas (which are many) where the map does not contain enough suitable topographic detail to enable the correlation between the map and reconnaissance photos to be done with certainty and accuracy.
The success of the artillery shooting at El Alamein was largely due to accurate survey both by R.E. and R.A.
The importance of obtaining complete, good quality vertical air-photo Survey cover of possible combat areas, before the requirement becomes pressing urgent, and whilst enemy opposition is absent activity or inattentive, is more than apparent. It enables counter- battery measures of the kind described to be put into operation at the best in a matter of hours, and at worst in a matter of days; whilst it also has a wider application to Topographic mapping and to camouflage projects.6
The production of block plots at 1:25,000 scale was a joint effort by 512 Field Survey Company, which was the Middle East’s base production unit based initially at Abbassia, but later in the Tura Caves in the escarpment east of Cairo and, nearer the front, by 46 Company S.A.E.C. (South African Engineer
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