Enigma variations

Code breaking trimmed two years from the Second World War, says the blurb on the back of Action This Day (Transworld, £14.99). Editors Michael Smith and Ralph Erskine make good work of showing you how tough a job and how great a triumph that was for the people of Bletchley Park, Hertfordshire, where the Nazis’ Enigma code was cracked. New Scientist’s reviewer recommended it: “Priceless anecdotal and technical detail”. It’s a read for enthusiasts, those who can already tell their “Purple” from their “Floradora”.