Molemot,
When you first mentioned
...My father was involved with radar and so forth in WW2; he was, to start with, a Calculator Maintenance Engineer..
These would have been the "Comptometers" which were in use in those days. But I immediately thought "
Ultra", only to find that you have the story, later on, of the Post Office engineer who put into practice Turing's momentous ideas.
"Colossus" played a major part in winning the war, and one of the most wonderful things in the whole "
Ultra" story was that German Intelligence, right to the end, could never accept that "
Enigma" could be broken (and indeed the full story was not made public here for fifty (?) years).
Danny.