Military intelligence, neglected in the pre-war period, had by mid-1942 proved itself indispensible through its gathering of information from radio messages coded 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 some of the steps by which he and others developed the new type de-crypting system and in the process provides a candid glimpse of British intelligence both past and present.