British codebreakers at Bletchley Park successfully broke the German Enigma code used on the Eastern Front. This key, codenamed "Vulture," allowed British intelligence to gain insight into German military plans and operations, which ultimately aided the Allied war effort. Winston Churchill, recognizing the value of this intelligence, instructed that the information be shared with Joseph Stalin, the leader of the Soviet Union. The code breaking remained classified for decades after the war.
By Alessandro Nassiri - Museo della Scienza e della Tecnologia "Leonardo da Vinci", CC BY-SA 4.0