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Abstract

This article examines the insecurity of British naval communications during WW II, when the Royal Navy relied on super-enciphered book codes, instead of the British cipher machine, Typex, to encrypt its signals. Kriegsmarine codebreakers consequently found it relatively easy to read American-British-Canadian messages about the Atlantic convoys, which led to heavy allied ship losses. However, the British official history of intelligence’s claim that “by 1939 the Admiralty had rejected the use of the Typex machine in ships” is categorically wrong -- only slow production prevented Typex entering service on ships. The US Navy criticised the use of a codebook for American-British-Canadian convoy work, but the American Chiefs of Staff banned the supply of an American high-level cipher machine to the British. The article explains why Typex (which was an improved version of commercial Enigma) was much more secure in practice than Wehrmacht Enigma, and describes the development of the Combined Cipher Machine (CCM) for joint use by the US, British, and Canadian navies. The CCM, and a post-war NATO version, are shown to have been very insecure, but wartime German codebreaking agencies could not break it