Steffen, Dirk (2004). "The Holtzendorff Memorandum of 22 December 1916 and Germany's Declaration of Unrestricted U-boat Warfare". The Journal of Military History. 68 (1): 215–224. doi:10.1353/jmh.2003.0412. S2CID159765016. Project MUSE50680.
Steffen, Dirk (2004). "The Holtzendorff Memorandum of 22 December 1916 and Germany's Declaration of Unrestricted U-boat Warfare". The Journal of Military History. 68 (1): 215–224. doi:10.1353/jmh.2003.0412. S2CID159765016. Project MUSE50680.
Steffen, Dirk (2004). "The Holtzendorff Memorandum of 22 December 1916 and Germany's Declaration of Unrestricted U-boat Warfare". The Journal of Military History. 68 (1): 215–224. doi:10.1353/jmh.2003.0412. S2CID159765016. Project MUSE50680.