FWIW, in WWI, many troops were issued pistols/revolvers, much of the reason M1911 pistols were scarce and Colt and S&W were asked to produce revolvers for the .45 ACP cartridge. At that time, squad leaders, assistant squad leaders, all company grade officers, machinegunners, assistant machinegunners, MPs, etc., etc. all carried pistols. Many of them couldn't hit anything with a handgun. The carbine was intended to replace almost all those pistols with a short, light rifle that would be easier to hit with and yet easy to carry for men whose duties involved other than direct engagement with the enemy or whose primary weapon was something other than the infantry rifle.
The pistol had been a primary fighting weapon for quite some time. Before repeating firearms or efficient breech loaders came along the only way to have a fair number of shots to fire in a fight was to carry several handguns.
It was not uncommon for some members of naval boarding parties to carry four or more single shot pistols slung around the neck by cords, or clipped to belts or bandoleers.
Black Bread the pirate carried at least nine pocket pistols on a bandoleer besides several full size boarding pistols.
I've seen photos of a unusual accessory for the 1911 pistol. It was a canvas wrist strap for the gun hand with about a half dozen or so magazines attached by cords through lanyard staples on the mag floor plate. This allowed rapid reloading when driving off pirates or defending a gunpit from charging infantry.
Another USN accessory was a pistol rack holding four 1911 pistols in simple leather holsters nailed to the board and a hand grip cut into the board. You could carry two of these in each hand if necessary to distribute pistols to the crew in case they had to repel boarders.
Pistol Carbines were around for a century or more before WW2, starting in the single shot muzzle loader days. They gave the compact carry of a handgun but allowed for a longer effective range.
The Colt revolvers improved on the pistol carbine, but repeating rifles made them obsolete till autoloaders like the C96 and artillery Luger came along.
During WW1 the Winchester self loading rifles were used to some extent, mostly by the French, in much the same manner as the M1 Carbine would be used in later years. There was even a heavily modified Winchester self loader entered in the trials that settled on the M1.