Churchill and Intelligence: Enigma and Ultra
How Churchill used the Ultra secret -- the breaking of German Enigma codes -- and the agonizing decisions it forced on him.
Bletchley Park and the Breaking of Enigma
The Enigma machine, used by Germany's armed forces to encrypt their communications, was considered unbreakable. Its rotor-based system could produce 158 million million million possible settings. But British codebreakers at Bletchley Park, building on pioneering work by Polish mathematicians who had first cracked earlier versions of Enigma, achieved what Germany thought impossible.
Alan Turing and his colleagues at Bletchley Park developed electromechanical machines called 'bombes' that could test Enigma settings at high speed. By 1940, they were regularly reading German Luftwaffe communications. By 1941, they cracked the more complex naval Enigma used by U-boats -- a breakthrough that proved decisive in the Battle of the Atlantic. Later in the war, they broke the even more sophisticated Lorenz cipher used for high-level German strategic communications.
The intelligence derived from these decrypts was codenamed 'Ultra.' At its peak, Bletchley Park employed over 10,000 people and was processing thousands of decrypted messages daily. It was one of the greatest intelligence achievements in history, and it remained secret until 1974, nearly thirty years after the war ended.