Series Number Id: UNKNOWN. Sheet number: parts of 51b SW, SE, & 57c NW, NE. Edition number: 4d. Trench map and enemy battery positions map. "Special sheet." "Detail and trenches corrected to 26-8-17." "Field Survey Co., R.E. (10027)." Detail, contours and grid grey; woods green; trenches in red; zone call markings in blue; approximate British front line 4-9-17 in blue., WW1 Trench Map Collection: Box PC27, Envelope 783.