The Emperor's Codes moves across the world from Bletchley Park to Pearl Harbor; from Singapore to Colombo; and from Mombasa to Melbourne, describing not just how the Japanese codes and ciphers were broken but how the lives of the codebreakers, both professional and personal, were affected. It tells the stories of John Tiltman, the eccentric British soldier turned codebreaker who made many of the early breaks into Japanese diplomatic and military codes; Eric Nave, the Australian sailor recruited to work for the British who pioneered breakthroughs in Japanese naval codes; and of Oshima Hiroshi, the hard-drinking Japanese ambassador to Berlin, whose candid reports to Tokyo of his conversations with Hitler and other high-ranking Nazis were a major source of intelligence in the war against Germany. Many of these revelations have been made possible only through using declassified British files, through privileged access to Australian secret official histories, and interviews with a number of British, American and Australian codebreakers.