PerSec is Personal.
I never introduce RAF when I first meet someone. If pressed Civil Service and that is sufficiently boring to switch people off. That is until I saw in the paper someone saying what when someone works in the civil service it is either Fire, MGS, Job Centre, Foreign Office etc, except those who say civil servant - they work for MOD.
Once, many moons ago, we were at a camp site next to a German couple, he had a Herr Flikk of a limp. Innocently Mrs PN asked the wife what had happened.
"Oh it was during the war, the RAF you know. What does your husband do?"
Oh he just works in an office.