Two wheels from the four-rotor German Enigma cypher machine, 1939-1945.
© Science Museum / Science & Society Picture Library
The two code wheels displayed here show the electrical contacts between adjacent wheels. The four-rotor Enigma cypher machine, devised by the German Navy in 1939, was used to encode wartime mesages requiring a particularly high degree of security. The search to crack the the Enigma codes also resulted in 'Colosus', the first all-electronic digital computer. The cracking of German cypher codes by Allied intelligence was a major achievement in cryptanalysis and played a key role in the outcome of the North Atlantic U-boat engagements.