In less than six hours in August 1942, nearly 1,000 British, Canadian and American commandos died in the French port of Dieppe in an operation that for decades seemed to have no real purpose. Was it a dry-run for D-Day, or perhaps a gesture by the Allies to placate Stalin’s impatience for a second front in the west? Historian David O’Keefe uses hitherto classified intelligence archives to prove that this catastrophic and apparently futile raid was in fact a mission, set up by Ian Fleming of British Naval Intelligence as part of a ‘pinch’ policy designed to capture material relating to the four-rotor Enigma Machine that would permit codebreakers like Alan Turing at Bletchley Park to turn the tide of the Second World War.