@Mick Gower
The Poles got hold of a commercial enigma machine by intercepting it in the post, figured out how it worked, put it back in the post and then did a runner to Paris with the information, which got passed to allied forces. The enigma was around in the early 30s and there are numerous different versions.
Turing and Welchman figured out that one of the best ways to find the settings for a given day was to find out which settings were impossible - thats what the bombe does, it rules out combinations that are impossible and leaves a reduced set of possibilities to be tried.
If you are interested in the whole story I reccomend reading is "Enigma" by Hugh Seebag-Montefiore. Its an excellent book that covers the first creation of the enigma machines as a commercial unit for banks etc to use right through its development as a military machine and the struggle to break the code as well as introducing many of the famous names from Bletchley.
Biting the hand that feeds IT
