Secret, Watten Bridge Head - Merckeghem Switch - St. Omer - Sercus Line : artillery positions
Series Number Id: UNKNOWN. Sheet number: part of sheet 27. Secret, Second Army rear defences, July 1918. Title statement in red overprint. "[4th] Field Survey Bn. (9458B) 15-7-18." Grey base map. Main defence line, HQs and OPs in red; gun and howitzer positions in black., Location: Research Collections; Fonds: WW1 Trench Maps: France; Box number: PC19; envelope_number: 578.