This book, about the history of codebreaking during the second world war, didn't really grab me, I'm afraid. The eponymous machine itself was barely mentioned until almost half way through and it didn't seem to have focus. That was the point, I suppose, it was providing an overview, but it was never really able to hold my interest properly.

It was interesting to learn about the different types of enciphering that went on during the war, though, and the fact that the British government, when it eventually got around to releasing the papers about them, went out of its way to downplay Colossus and the Ultra code by playing up Enigma.