Top Secret Ultra

Bletchley Park, a modest estate some fifty miles northwest of London, was the site of one of the closest-held and longest-kept secrets of World War II. Most Secret Ultra, renamed Top Secret Ultra when America joined the venture, conveyed a staggering amount of intelligence on enemy movements and intentions to Allied field commanders. This was obtained by steady monitoring of German radio transmissions, and was made possible by a major feat in scientific detection: the breaking of the German Enigma machine ciphers."--Book Jacket.