After more than 40 years, this is still arguably the most significant book on the explanation of destruction of the German war machine in the West in World War II.
Word for word, no other book so succinctly explains the single most important reason behind for the Anglo-American triumph over Hitler's armies - and simultaneously dulls the reputation of many of the `great' Allied military machismo's.
No postwar gung-ho, breast-beating memoir can be properly adjudged without reference to the up to (according to some sources) 90 000 decoded Enigma signals per month in mid-1944 that were fed to all the top American and British commanders as Ultra intelligence and spliced into Intelligence summaries at the lower echelons as well.
Winterbotham, who was in charge of the distribution of the Ultra intelligence to the highest levels, was perfectly placed to assess the critical impact of this information.
As much as Ultra resolves one mystery, it opens another: How was it possible that the German military, who were continuously checkmated at the strategic and tactical level in every major operation from Battle of Britain, North Africa, Italy and finally Normandy, never realised or figured that their signals were being intercepted...? Can overweening complacency, arrogance, stupidity alone explain this? (Obviously the fact that the Allies were using the crytographically uncrackable OTP system (and more?) hid the technical hint of this)
To his credit, Hitler must have had massive suspicions after Falaise, and that is why he banned all radio transmissions in the planning of the Ardennes Offensive, which led to spectacular opening results (as had been the case in 1940 before Bletchley got into gear).