Enigma en.wikipedia.org/wiki/Enigma_machine is the name of a family of ciphering machines made famous by their use in World War II.

Before the war, the German military adopted the Enigma machine as a means of enciphering highly sensitive wireless communications. First the Polish, and then the British spearheaded efforts to decrypt Enigma messages. The importance of this mathematical struggle was kept largely secret until the early 1970’s. After details were released, analysis of the war was to some extent re-written to take into account the use of this vital source of intelligence.

The intelligence gained through this source — codenamed ULTRA en.wikipedia.org/wiki/Ultra_(WWII_intelligence) — was a significant aid to the Allied war effort. The exact influence of ULTRA is debated, but a typical assessment is that the end of the European war was hastened by two years because of the decryption of German ciphers. Dwight D. Eisenhower, was said to have described Ultra as having been "decisive" to Allied victory in World War II.

Much to the Allied codebreaking work was carried out at Bletchley Park en.wikipedia.org/wiki/Bletchley_Park in England. Churchill referred to the Bletchley staff as, "My geese that laid the golden eggs and never cackled." Churchill is also quoted as telling King George VI: "It was thanks to Ultra that we won the war." Churchill's greatest fear, even after Hitler had suspended Operation Sealion and invaded the Soviet Union, was that the German submarine wolf packs would succeed in strangling sea-locked Britain. He would later write, in Their Finest Hour (1949): "The only thing that ever really frightened me during the war was the U-boat peril." A major factor that averted Britain's defeat in the Battle of the Atlantic was her mastery of Naval-Enigma decryption.

Bletchley's role in breaking the German, Italian and Japanese signals codes is held by many historians to have been the paramount factor in the Allied victory of 1945.

The machine in this picture has an unusual story behind it: