'Gannon's book contains a mass of utterly fascinating and largely unknown material about an immensely important wartime project, and is very welcome indeed.' Brian Rendell, TESIn 1940, almost a year after the outbreak of the Second World war, Allied radio operators at an interception station in South London began picking up messages in a strange new code. Using science, maths, innovation and improvisation Bletchley Park codebreakers worked furiously to invent a machine to decipher what turned ou