Reddit reviews Colossus: Bletchley Park's Greatest Secret

If you haven't read it already, you might want to check out David Kahn's The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet.

He's not joking when he says it's comprehensive: it's 1200 pages. Absolutely fascinating if you're at all into the history of crypto; it goes into a lot of detail about not only how historical cryptosystems worked, what were their weaknesses and how they were cryptanalyzed etc., but also the historical context in which the systems were used and developed.

Edit: Just realized the Colossus book I was thinking of was this. I'll have to check out the one you linked to