Two excellent short books by authors who participated, at Bletchley, in the intelligence handling of high-level German cipher take during World War II. Calvocoressi's gives a vivid view of the whole operation, from intercept to outgoing signal to the commands, with a few highlights on the importance of ULTRA in the conduct of the war and a deserved tribute to the initial Polish contribution. Bennett, using the now available file of 25,000 outgoing signals, examines in definitive detail the unique picture ULTRA provided in the climactic phase of the war. His defense of intelligence performance in relation to the Arnhem debacle is totally convincing, on the failure to spot the Ardennes offensive a shade less so.