Encrypted communications were used by all major military powers by World War II, so the ability to crack methods of encryption was vital to maintaining the upper hand in strategic decisions. The Germans used the Enigma machine and its successors, the much more powerful Lorenz SZ40 and SZ42, to encrypt and decrypt messages containing sensitive information. Initial breakthroughs by Polish intelligence before the war led to success in cracking the early Enigma codes. This knowledge was passed to the British and formed the basis of the effort by cryptographers at Bletchley Park to deduce the logical pattern of the Lorenz cipher after it came into use in 1941. Lorenz wireless traffic, which became known as ‘Fish’, could be intercepted by British intelligence from 1942 onwards, with each line of communication between key cities under German influence being given an individual name. Many key pieces of ‘Ultra’ (the British designation for encrypted enemy communications) information were received from Fish intercepts throughout the war.
— OR —