This is the first book to detail British wartime successes in breaking Japanese codes. Other veterans of Bletchley Park (GCHQ) have described how they broke the German Enigma machine to produce Ultra intelligence, and how that helped to hasten victory. There have also been accounts of how the US broke the Purple cipher and a naval code, even before Pearl Harbour. The Book, however, chronicles the British achievement at Bletchley Park and in the Far East of breaking Japanese codes of dazzling variety in Burma three months before Hiroshima.

This first-hand account shows the magnitude of the task: grappling with one of the world's most daunting languages, learning the skills of cryptanalysis, turning out decrypts against the clock, and weaving together all the strands of intelligence to help vanquish a dogged and resourceful enemy who had never known defeat - in perhaps the worst climate and terrain in the world. It is success story that conveys the sheer excitement of reading the enemy's mind, and contains some surprises: who would have expected Japanese signals to reveal not only what they were up to in Asia but also details of German jet aircraft, the latest U-boats, even Normandy beach defences?