Enigma

Enigma was designed at the end of the First World War by Arthur Scherbius and sold as a commercial machine. The German navy used it from 1926, followed by the army and the air force. Its rotors changed the encipherment with every key pressed, so the Germans believed it unbreakable.

At the Polish General Staff’s Cipher Bureau, Marian Rejewski, using mathematics rather than linguistic methods, read the first messages in December 1932; with Jerzy Różycki and Henryk Zygalski he went on to build devices including the cryptologic bomb. In July 1939, at Pyry near Warsaw, the Poles handed their methods and replica machines to the Allies. On that basis the British at Bletchley Park read Enigma traffic throughout the war, and the intelligence codenamed Ultra helped above all in the Battle of the Atlantic.