The Germans did introduce a new, four-rotor version of their Enigma machine in February 1942, and the code was practically unbreakable by the Allies until the capture of associated code books from a submarine, in October 1942. "Shark" (as the Naval Four Rotor Enigma cipher was know by Bletchley Park) was broken regularly from December of that year (sources include Bletchley Park). But in real life, this was a British operation, and did not involve a deception like that depicted in the film. The sub itself, the U-559, sank shortly after the code books were removed.

Film

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