This photograph shows the cipher machine “Enigma,” which was used by the German army beginning in 1937. Orders and messages were encrypted by five electronic rollers; the recipient of a message would receive signals via a synchronized device and would then decipher them with the aid of a specific key. Both the code and key were changed every 48 hours. In the spring of 1940, the British Secret Intelligence Service (SIS) managed to crack the code with the help of Polish mathematicians. This breakthrough gave the Allies a key strategic advantage. The German military thought it was impossible to crack the “Enigma” system and therefore kept using it until the end of the war. The successful deciphering of the “Enigma” code was not made public until 1974. This photograph was taken on board the submarine U 124, which was stationed at the German base at Lorient, France, at the time of the photo.