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A version of the Enigma machine—an encoding device that was used by the the Nazis to encrypt messages during World War II—is going up for auction at Christie's in London on Sept. 29. The Enigma was produced by a Dutch company but was bought exclusively by the German military in 1929. It was the most sophisticated and complicated messaging device of any encoding models during the World War II years; it would encode messages before sending them via Morse code to another Enigma and was used for espionage. Nazi Germans believed its complicated settings were "impossible to crack," but a group of code breakers based in England ultimately figured out how to decode its messages. Some historians believe it significantly affected the war's end and even had an impact on who won.