Series Number Id: UNKNOWN. Sheet number: 57D NE. Edition number: 3. Battle of the Somme, Gommecourt salient: front lines, artillery intelligence, enemy battery positions, trench mortars and rear organisation 1-1-17. "Ordnance Survey, December 1916." "3rd Field Survey Co. R.E (1266)". Detail, grid and contours grey. Overprinted with pecked purple British front line and pecked orange-brown German front line. Overprinted in purple: [German 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 PC15, Envelope 416.