STetc ch 20 - the espionage community

[Michael Bailey]

Pip and Alf are quite informative. It's all news to Hicks, pretty much; typical Pynchon reader might have some familiarity but it's worth reviewing anyway.

MI3b - this was a real division of British Intelligence between the wars.

I don't find a reference to an "F", but the Mansfield Smith-Cumming on whom this "F" models his use of one letter as an identifier was the founder of the British Secret Services, which became MI5 and -6.
https://allthatsinteresting.com/mansfield-smith-cumming

He went by "C" because he had hyphenated with his wife's name, thus the -Cumming.
Tempting as it is to hypothesize, it wasn't C himself, but someone in his shop who came (no pun intended) up with a notion that found its way into Pirate Prentice's praxis in Gravity's Rainbow:

"A researcher working for Smith-Cumming discovered that semen could be used as invisible ink — which led to the popular interagency joke that “every man his own stylo.”
The idea was later dismissed, because of the smell."