1. DMO/ADD/70 Reference (shelfmark): DMO/ADD/70 Title: 'Report on Heligoland Defences. Issued by General Staff, War Office, January, 1921.' 'Secret.' Collection Area: Map Collections Languages: English Date Range: 1921 Extent: 1 volume (41 pages, including 2 maps, 10 plans, and 29 photographs).