The Cambridge mathematician sworn to secrecy at Bletchley

In the spring of 1941, a brilliant mathematics student from Cambridge received a discreet summons. He was sent to Bletchley Park, a Victorian manor in Buckinghamshire housing the Government Code and Cypher School. Even before learning the nature of his work, he was presented with the Official Secrets Act to sign: the oath never to reveal, to anyone and for life, what was done behind those walls. Should he commit to this absolute silence, decline, or speak of it to his family?

Behind the barbed-wire fence a decisive secret battle was being waged: the breaking of the German Enigma machine. In Hut 8, the team of the mathematician Alan Turing tackled the naval version, the most complex, which protected the U-boats devastating the Atlantic convoys. On 9 May 1941, during Operation Primrose, the Royal Navy captured the submarine U-110 and recovered an intact Enigma machine and its codebooks.

The master weapon was the "Bombe," an electromechanical machine designed by Turing and improved by Gordon Welchman, which tested thousands of rotor settings at high speed. The site, at first a few dozen people, numbered nearly ten thousand at its peak, the majority of them women. Mathematicians, linguists, chess champions, and crossword enthusiasts were recruited there in the utmost secrecy.