Series Number Id: UNKNOWN. Sheet number: 57D NE. Edition number: 2D. Battle of the Somme, Gommecourt salient: artillery intelligence, German battery positions and arcs of fire 4-12-16. "Trenches corrected to 7-9-16"; in purple overprint below, 4.12.16." "Ordnance Survey 1916." "3rd Field Survey Co. R.E. 3rd Army (1221)". Detail, grid and contours grey; water blue. German trenches red; British front pecked blue. Overprinted in purple: [Germany battery positions and arcs of fire]; Reference; list of square positions of trench mortars. Purple, green and orange-brown plates registered with needles. Overprinted green: military tracks and observation posts. Overprinted orange-brown: light railways and supply dumps., WW1 Trench Map Collection: Box PC16, Envelope 434.