The Germans used the Enigma cipher machine for their military communications before and during WWII. In August 1941, the British managed to capture an Enigma coding machine from U-570. The first and only U-Boat to be captured by an aircraft…
On the morning of August 27, 1941, U-570 under the command of Kapitänleutnant Hans-Joachim Rahmlow was patrolling submerged about 80 nautical miles south of Iceland. Unable to reconnoiter at periscope depth due to choppy seas, Rahmlow ordered the German submarine to be surfaced. The U-boat did so — almost directly beneath a British Hudson bomber on anti-submarine patrol. As the Hudson dove to attack, Rahmlow ordered a crash dive, but before U-570 could escape, it was bracketed with four depth charges. The U-boat suffered only minor damage, but the inexperienced crew, many suffering acutely from seasickness, panicked. Even though Rahmlow had spent many years in the German navy, he was new to U-boats and U-570 was his first operational command. He ordered the submarine to surface again and, after being strafed by the Hudson, the crew of the U-570 unfurled a white sheet. Rahmlow, meanwhile, sent out a radio message to U-boat command stating what happened and that he had surrendered. U-570 was the first and only U-boat to be captured by an aircraft.
There are conflicting accounts about the crew’s subsequent actions in the U-boat, particularly on whether or not they were successful in destroying and/or tossing overboard codebooks and the Enigma cipher machine. All accounts published in the immediate aftermath of the incident claimed that the German sailors were able to destroy and toss overboard all cipher machines and codes. This, of course, made sense because the last thing the British wanted was for the Germans to believe that they had captured code books and an enigma cipher machine.
But, a confidential U.S. Navy report of the incident noted that during the initial examination of the boat, and while the crew was being removed “British intelligence officers from Iceland arrived; and thinking that the ship would undoubtedly sink very soon, they started a very hurried and rather unorganized examination . . . and also began to remove all books, papers, plans, etc.” And later on, noted, “At least one German receiving or transmitting instrument had been removed . . . by the British.” A little later, the report more tellingly noted: “A large cabinet had been removed from the forward corner of the control room by admiralty personnel soon after the capture and sent to England. . . . In view of the vagueness of the information on the site as to the exact nature of this instrument it is considered important that accurate information be obtained from the Naval Attaché London.” [Emphasis in the original.]
The U.S. Navy officers writing the report were justified in their suspicions. Edward Thomas was a Royal Navy intelligence officer stationed in Iceland at the time of the incident and participated in the inspection of the U-boat. He later wrote, “I wondered why the highly knowledgeable civilian intelligence officer . . . was so excited by the discovery of an empty wooden box, which he said had contained a cipher machine, with four slits on the shelf of one of its compartments.” As he later learned, it was designed to contain an updated version of the encryption machine known as Enigma.