22 “Whenever any of their vessels”: History of Room 40, CLKE 3, Clarke Papers.
23 a sense of the flesh-and-blood men: Reports derived from interrogations of captured U-boat officers and crew yield a sense of U-boat life far richer than that provided by any other published memoir or book. Admiralty Papers, ADM 137/4126, National Archives UK. Specifically, see interrogations involving crew from U-48, U-103, UC-65, U-64, and UB-109; see also Grant, U-Boat Intelligence, 21.
24 They used their wireless systems incessantly: Beesly, Room 40, 30.
25 “extreme garrulity”: History of Room 40, CLKE 3, Clarke Papers; Beesly, Room 40, 30.
26 “I fooled ’em that time”: New York Times, May 8, 1915.
27 Room 40 had long followed: “Capt. Hope’s Diary,” Admiralty Papers, ADM 137/4169, National Archives UK.
28 Addressed to all German warships: Record of Telegrams, March 3, 1915, Norddeich Naval Intelligence Center, Admiralty Papers, ADM 137/4177, National Archives UK.
29 “Four submarines sailed”: Intercepted telegrams, April 28 and 29, 1915, Admiralty Papers, ADM 137/3956, National Archives UK. Anyone examining these files will note, to his or her pleasure, that these are the actual handwritten decodes.