The story of cracking the secret German Enigma Machine codes at Bletchley Park is well known, but on 9 May 1941 an extraordinarily brave salvage team boarded a sinking German U-boat and seized one of the encryption machines.
The U-boat was chased and hit with a depth charge. It surfaced after being badly damaged, and the bold decision was made to board it and remove anything that might prove valuable.
A sublieutenant named David Balme, who was given the job of leading the boarding party, found it empty and ‘abandoned in great haste’. When one of his men saw what looked like an unusual typewriter, bolted down and ‘plugged in and as though it was in actual use when abandoned’, he unscrewed it, managing to carry the heavy machine out and onto HMS Bulldog. Such a device had never been seen before. The salvage team also took various codebooks. This little heralded moment of bravery was one of the most significant of the war, assisting in the breakthrough that is credited with shortening the war by years and saving countless of lives. Source
Realising the importance of not alerting the Germans that an Enigma machine had been captured, Winston Churchill didn’t even inform President Roosevelt, his closest ally.