Further developments in the secret history of the Enigma code machine which was the single most important intelligence advantage the Allies had over the Axis. Ultra was the British code word for messages relating to Enigma, and meant ""ultra top secret."" The basic story of the British cryptoanalysts and the Enigma is told in F. W. Winterbotham's The Ultra Secret', the present book expands upon strategical uses of the broken German code in various battles. The Enigma was first developed by a private German firm in the early Twenties and was eventually adopted by the German military. When the Poles caught wind of the device, they managed to build several copies, and when Poland fell they shipped one to the French and two to England. Throughout the war, the British trembled over the possibility that the Germans might find out that their enemy had long been in possession of their secret radio codes (the Japanese Purple machine, an Enigma variant, had already been broken by the Americans). On the other hand, possession of Ultra gave some commanders overconfidence at the wrong times, especially during Operation Market Garden, when they refused to believe their own intelligence that the Germans had massed armor at Arnheim, and as a result our troops were slaughtered. The drawback of Ultra was that it led Allied commanders to accept at face value the troop and battle strengths that German commanders mis-represented to their superiors so that they could get more materiel. . . . Revealing, but too dense for wide readership.