The last of three talks by Peter Calvocoressi , wartime intelligence officer at the Government Codes and Ciphers School.
Knowing exactly what the German military were saying to each other by secret code - deciphered by a British copy of the Enigma machine - was the ' ultra secret' of the Allies during the last war. But what use was made of this intelligence, and can it be asserted that some battles were won largely because of our detailed knowledge of Nazi secrets?
(If ... is tomorrow's programme in The Secret War: BBC1 9.25 pm)