Series Number Id: UNKNOWN. Sheet number: 5a. Edition number: 2. "Secret" in upper right margin. In upper left margin: Belgium 1:100,000. "Ordnance Survey, (O.B.) August, 1918." Grey and blue base map [from series GSGS 2364, but does not carry this designation]; overprint in black and red. Includes inset map: Aire, scale 1:20,000 [First Army headquarters]. Purple stamp in lower margin: Zinc Printing Dept., Proof, 3 Sep 1918, O.S.O. Overseas Branch., Location: Research Collections; Fonds: WW1 Trench Maps: France; Box number: PC20; envelope_number: 620.
