The Turing Digital Archive contains nearly 3,000 images of letters, photographs, newspaper articles, and unpublished papers by or about Alan Turing. The images were scanned from the collection of Turing papers held in the Archive Centre at King's College, Cambridge. The images are subject to copyright restrictions.
The Enigma and the Bombe http://www.ellsbury.com/enigmabombe.htm
Alan Turing http://en.wikipedia.org/wiki/Alan_Turing
Solving the Enigma: History of the Cryptanalytic Bombe http://www.nsa.gov/about/_files/cryptologic_heritage/publications/wwii/solving_enigma.pdf
Enigma Cipher Machine http://www.cryptomuseum.com/crypto/enigma/