Turing's Bombe
Designed by Alan Turing and Gordon Welchman in 1940, the Bombe was an electromechanical
device that automated the search for Enigma rotor settings. It exploited "cribs" --
known or guessed plaintext-ciphertext pairs -- to eliminate impossible rotor configurations.
Over 200 Bombes were built at Bletchley Park, each with 36 Enigma-equivalent units (108 rotors). They could test all 17,576 positions for three rotors in about 20 minutes, finding "stops" where the crib was consistent.