Research undertaken over a 15-year period by military historian David O'Keefe uncovered 100,000 pages of classified British military archival files that documented a "pinch" mission overseen by Ian Fleming (best known later as author of the James Bond action espionage books), that coincided with the Dieppe Raid.
The introduction of a 4th rotor in 1942 was preventing cryptanalysis of the German naval Enigma, and led to a strong resurgence in German U-Boat attacks on the vital Atlantic convoys coming from North America.