A very thorough history of the role the code breaking in Bletchley played during the war years, also a portrait of those involved from high up to the people doing day to day work.
I found this a really interesting read, the book describes well the code breaking mechanics without getting too bogged down in detail. It ties historical war events to the background code breaking. I had never appreciated that the location of Bismarck, the North Africa campaign, the Atlantic convoy war, and keeping Russia in with intelligence had all benefited from code decrypts.
Throughout the author is at pains to explain the secrecy involved, to the extent that some information could not always be used because it would betray the source. This secrecy continued way after the war, it was not until the 1970s when a book was released about the "Ultra secret" that the first signs appeared.
Non use of information has some controversy, the book argues that it was not responsible for allowing Coventry to be bombed without any evacuation, or for not informing the Americans of Pearl Harbour.
The accepted truth is that the code breakers shortened the war by two years, I think that under sells them, keeping supply lines open in the Atlantic, and keeping Russia in with intelligence must have been a huge tactical advantage.
The post war secrecy is interesting, Britain missed out on the birth of the computer having ironically used something akin to them in the code breaking. Alan Turing was treated shamefully and killed himself in the early 1950s. The silence of those who worked at Bletchley is quite staggering, with some sad stories of people not being able to bring themselves to tell their families what their role was after many years.
Part of this maybe down to the compartmentalisation of the decoding tasks, huts on the park which did specific jobs and everyone working in a culture where you might not have known what was going on in other departments. Bletchley did have a brush with the Cambridge spy ring as they recruited from bright academic circles, and that sideline is also interesting with the author suggessting the British government was happy to let some information be divulged to the Russians this way.
