Marching Orders: The Untold Story of How the American Breaking of the Japanese Secret Codes Led to the Defeat of Nazi Germany and Japan

by Bruce Lee

Meanwhile, the British have been working on the codes used by the German military. They have succeeded in breaking the so-called Enigma codes (a name derived from a special code machine used by the German armed forces). Like the Americans, the British call their product of breaking the Enigma codes by a special term: Ultra.