Page 71 - Ranger Demo

maps, calculation of grid constants, and the plotting of enemy defences, which had been located on reconnaissance photos by the M.A.I.U. interpreters, for subsequent incorporation in defence overprints.
The fixation of targets was effected by first of all transferring their positions from reconnaissance photos to survey photos, the grid co-ordinates of whose principal points had already been determined and plotted on a skeleton block-plot. By means of radial line methods of intersection, the position of each target was fixed and its co-ordinates measured from the grid.
The programme was a continuous one, each move forward introducing a new set of targets whose positions were required by the C.B.O.s 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, and with the advent of bad weather conditions 7 General Survey Section was then temporarily removed from M.A.I.U. for other target work, returning again in time to carry out further target fixations before the spring offensive.
This target fixation work eventually came to an end late 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
Another source on Italy
(d) Block Plots for Fifth Army. AFHQ were asked to prepare block plots in areas in advance of the present Fifth Army front in which there was little trig control and in which the only air cover consisted of photographs in which the average tilt of a sortie was as much as 4 degrees 30 minutes. The multiplex equipment was used to locate for each photograph the “centre” which would be used for radial line plotting. Multiplex triangulation was used to bridge between the available control and was adjusted to the available control. With the Plumb Point located, the “centre” for each photograph was plotted on the multiplex plot and identified on the photograph. The “centre” was a point of detail near the isocentre in the case of flat country and about midway between the plumb point and the isocentre in the case of mountainous country.14
(d) Block-plots for target fixation. A programme of target fixation for counter-battery purposes by the use of block-plots was taken up during the winter, the work being done on 9 x 9-inch prints at about 1/50,000 scale, using large scale photos for identification. To cover the gaps in these block-plots, 15 Army Group asked for further 6-inch photography. The construction and operation of these block-plots was done by 7 General Field Survey Section R.E. and continued with success during the remainder of the war 11, Page 340, but not mentioned in the Index)
The source for the above note is possibly the War Diary of 517 Fd Svy Coy RE to which, at that time, was attached 7 General Fd Svy Section: -
29th Nov 44 - Orders to take over all block plot and def op work from 13 Coy.14
The Campaign in Normandy
The next reference to the use of block plots use is in Clough’s description of the work done in preparation for “Overlord”.
In case the “Benson Project” 1:25,000 scale maps of Normandy were not available in time for D-Day, a block-plot was produced for each 1:25,000 sheet in the Normandy area, on which the position of the principal points of each photo used in the compilation was plotted. The principal points were also marked on each original negative by a small fine cross, and duplicate sets of these marked and numbered negatives were made and issued to each of the field armies together with copies of the skeleton block-plots. By this means, in the absence of the maps themselves, detail plotting could be done overseas of small areas if the emergency should arise, and counter-battery plots could be built up on the El Alamein pattern. The principal
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