My father was a SP in the Air Force back in the mid-sixties. He was stationed in South Vietnam from 65-66. Often they would conduct patrols into nearby areas surrounding the Bien Hoa Air Base. So even though my father was Air Force he found himself performing in an Infantry role to some extant. He was issued a Winchester 1897 Trench Gun, a S&W Model 15 Combat Masterpiece , which he carried on his belt, and a 1911A1 Government which he carried in a shoulder holster. Yes he carried two full size handguns and a shotgun. The last couple months he was there he turned in the shotgun for an M16, but retained the 38 and 45. The theory was empty one handgun and then go to the other one if it came to that. In other words a "New York Reload" (of sorts). Several of the senior Non-coms were WWII combat vets who choose to go over with the Air Force when the Army Air Corp became it's own branch, separate from the U.S. Army, in 1947(?). Not knowing what to do with a bunch of grunts the Air Force made them sky cops.

Anyway they told dad and his fellow airmen that the secret to surviving a gunfight was to just keep shooting. Center of mass and shoot until your man went down. Basic and brutal. Nothing much about ammo caliber was ever said. Except to make sure you had enough of it.