In 1974, when the story of Ultra, the secret British program to monitor and decipher Germany's Enigma signals, was revealed, among the most shocked by the revelation that German codes had been broken during World War II were the German code makers themselves -- who still believed that they had used an impenetrable system. In this superb work of forensic history, Ratcliff asks why they were so sure. He contrasts the fragmented and hierarchical German intelligence system, in which there was nobody able to grasp how it worked as a whole, with the British system, more centralized but with a culture of information sharing. The British went out of their way to conceal how much they knew and how they knew it, while overconfidence left the Germans embracing every explanation for leaks but the right one. Reading the book requires attention to organizational structures and the principles of cryptanalysis, but it is well worth the effort.