Based on newly declassified documents, this is the first complete story of Allied code-breaking in World War II - the compelling tale of codebreaking's golden age. In 1939 cryptoanalysis was in its infancy, its practitioners' skills rudimentary and untried. The codebreakers faced huge barriers of official indifference and - from the military bureaucracy - even contempt for their work. Yet during the course of the war these men and women accomplished extraordinary feats of mathematical wizardry that turned the tide of many critical battles. New Stephen Budiansky tells their story. From the fight against the Nazi U-boats in the Atlantic, to the climactic showdown against Yamamoto's aircraft carriers at Midway, and the success of the D-Day invasion, Battle of Wits reveals the shadow war that lay behind the famous events of World War II, and breathes life into unsung heroes whose work has been wrapped in secrecy for decades. Drawing on literally thousands of previously unseen files, Budiansky provides lucid explanations of how the most impenetrable of Axis codes were actually broken - including the German ENIGMA and Japanese Purple machines - and traces the origins of the top-secret project, codenamed VENONA, that broke the Soviet spy codes in one of the most incredible cryptoanalytic feats of all time.