1st ed., 1978. 398 pp., 17 photo-plates. D.j., 24 x 16cm. FINE. The author presents a definitive account of the way in which German ciphers came to be broken, of the establishment and functioning of the interception centre at Bletchley Park, and of the process by which its intercepts were distributed to the service authorities whose plans they affected. More importantly, the author assesses the impact of ULTRA on the conduct of the war by land, sea and air. This is one of the most important books ever to have appeared on the Second World War.