The 'lower level' tunnels seem to be the 'Dumpy Level' excavated in 1942 - 1943. The plan is undated but might date from the end of the 1950s when the Admiralty abandoned its headquarters, as the tunnels are hatched in red crayon and the key indicates that this area was to be 'alienated - unoccupied'. The original was marked as secret and the copy is stamped 'secret'.
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Creator of Archive: Royal Engineers
Victorian Tunnel, Early 20th Century Military Headquarters