another etymological urban legend?

[Douglas G. Wilson]

"Son of a gun":

Isn't a rhyme as good as an alliteration?

The Cassell slang dictionary says it's euphemistic for "son of a bitch" ...
but derives the "gun" from "gonnof", which strikes me as unlikely.

Partridge doesn't give an etymology but dates it from early 1700's, and
points out a second meaning "soldier's bastard" [now obsolete, I think]
with an 1823 reference.

Farmer and Henley give the "soldier's bastard" definition and also the
general one, and quotes an 1867 reference which gives the "boy born on
ship" story.

Random House dates it from 1700-10 and says it's perhaps originally
"soldier's bastard".

MW (Web) gives 1708 and considers it a euphemism although without giving
explicit etymology.

Chapman considers it euphemistic but quotes the "boy born on ship" story.

I'm agnostic. Possibly there was a separate origin but even if so I think
the expression quickly found a career as a euphemism.

-- Doug Wilson