I had a book from the library recently which gave a history of Bletchly Park and the GCHQ establishment from the point of view of the people that worked there. In the final chapter it gave a summing up of what had been achieved by the cryptoanalysis effort. The author pointed out that one of the reasons that Bletchlys part was played down at the end of the war was that the Ultra secret had been kept so successfully that many Eastern block nations still used a deriavative of enigma to encode signals, some well into the 1960s. So to admit to what had been done would have had a significant effect on our SIGINT capacity in the cold war. Blessed if I can remember the title of the book but it was a fascinating insight into the work and the social factors of the time. One of which was that at one point only Classics academics were considered for the job, mostly by personal recomendation.
Only 'Proper' people were invited. Mathematicians and Physicists were considered to be too erratic and not the type at all!