Series Number Id: GSGS 3050A. Sheet number: part of Sheet 36. "O.S.O. 1915." Area north of Armentières. Detail black; German trenches blue, with names and numbers. British front not shown. Unsquared. Another copy of this sheet was received in the GSGS Map Room (War Office) on 18 April 1915, soon after printing., WW1 Trench Map Collection: Box PC18, Envelope 567.