Peep this. 6 years before the bomb was dropped. The term was already in use by then. They said they named it after the pilot's mother but with a name like that in the 40's nobody would take that risk.

Bringing Up Baby (1938) was the first film to use the word gay in an apparent reference to homosexuality. In a scene in which Cary Grant's character's clothes have been sent to the cleaners, he is forced to wear a woman's feather-trimmed robe. When another character asks about his robe, he responds, "Because I just went gay all of a sudden!" Since this was a mainstream film at a time, when the use of the word to refer to cross-dressing (and, by extension, homosexuality) would still be unfamiliar to most film-goers, the line can also be interpreted to mean, "I just decided to do something frivolous."[19]

(Edit: also Grant was made to put on a dress like most hollywood faggots)