The Ultra secret - F. W. Winterbotham

In 1974 it was this book that revealed to the world the Second World War's best-kept secret: the operation - based at Bletchley Park and codenamed Ultra - which cracked the German cypher machine, Enigma. F.W. Winterbotham, chief of the air department of the Secret Intelligence Service during the war, was the man responsible for the organisation, distribution and security of Ultra. Here is the personal story of how this most secret information was received and processed, how it was distributed to commanders in the field, and the vital role it played in Britain's survival in 1940 and 1941, and in later Allied victories. Scores of books have been written on the subject since, but The Ultra Secret remains a unique insider's story of the near-miracle of Ultra - 'the secret weapon that won the war', as Churchill called it.