Military intelligence, grossly neglected during the interwar period, had by mid-1942 proved itself indispensable through information gathered from intercepted radio messages in the supposedly unbreakable German Enigma cipher. Ralph Bennett, who worked for four years at Bletchley Park as a senior producer of the intelligence (Ultra') derived from the Enigma decrypts, illustrates in this collection of reprinted essays some of the steps by which he and others developed the new type of information and in the process a candid glimpse of the workings of British intelligence both past and present.