[richieb]

The story of the Enigma is quite complex. But by 1941 the Allies knew how the machine worked (there were commercial Enigmas sold before the war). The Naval Enigma was somewhat more secure (more rotors to choose from) and obtaining the daily setting book would be the most important thing, not the machine itself.

Polish mathematicians broke the early Enigma in the late 1930s (http://www.codesandciphers.org.uk/virtualbp/poles/poles.htm), they passed their information to the British in 1939 and that was used as a starting point of the work at Blechley Park.

If you are interested in the details, check out the book "The Hut 6 Story" by Gordon Welchman. He was a peer of Turing who worked on the Army and Air Force Enigma, while Turing worked on the Naval version.

Of course Turing's biography by Andrew Hodges also has a lot of details how the Engima was broken.

[yoodenvranx]

I was always wondering if Neal Stephensons "Cryptonomicon" is historically accurate when he writes about the enigma and its background.