for unlawful carnal knowledge

Popup, Peruvian in this sense is in the OED

Aahhh! Thank you bibliophage! That would put it quite a few years before radar, which is otherwise quoted as among the first acronyms.

Ddin’t we have SCUBA before RADAR?

I think it’s pretty clear that “radar” was not the first acronym. It may be true that “radar” started the fashion of acronyms. Before “radar” acronyms were fairly rare, but afterwards they became reasonably common. It wasn’t till after the appearance of the word “radar” that people began to make up these absurd etymologies using acronyms.

No. Radar was 1941, scuba was not in print until 1952. This is odd, because it was invented nine years earlier.