What is the origin of the phrase under the gun?

Answer 1

This phrase originated with besieging a fortress or castle equipped with artillery The final step of the siege was to throw infantry against the broken walls, but also into the artillery battery remaining on the unbroken walls or inside the fortress The attacking infantry was literally 'under the gun' to complete its assault promptly

Answer 2

From the U.S. Navy publication Nomenclature of Ships(John Snelling, 1981), the phrase "son of a gun" is described as: : In an attempt to keep down the large number of deserters in the British Navy, the sailors were kept on board their ships while in English ports. But "wives" were allowed on board; one per man, with no questions asked. Cramped conditions on the ships caused the "ladies" to sling their hammocks between the guns in the 'tween decks. The phrase "son of a gun" originated here. In fact, the expression questioned the legitimacy of anyone. The old definition of a man-o'-war's man was "Begotten in the galley and born under a gun. Every hair a rope yarn, every tooth a marlin's spike, each finger a fishhook and in his blood, right good Stockholm tar."However, the actual origin might just be another nautical myth.

Answer 3

The earliest use of the phrase was when, during the 1800's, the British used this phrase for babies (maybe just boys, specifically) who were born at sea. This would occur when British sailors would take women along on their voyages.

"Son of a gun", as an expletive, doesn't make all that much sense with this information, since you'd never shout "IDIOT!" as an exclamation of emotion, but it seems to go well with how some people might say "why you son of a gun" or whatever.