"Shotgun! Shoot 'im 'fore dey run now..."

Sorry for the title. The refrain, hell most of the lyrics entire, from "Shotgun" by Junior Walker and the Allstars. Add "Do the jerk, baby. Do the jerk now" and you now know virtually all the words of this '60's classic.
Anyway, shotgun. One trick the Yanks brought to the party in the first war was the weapon pictured above. Surprisingly, no one had thought of the massive stopping power of these rather mundane tools before. I mean... they're made to shoot ducks for Christ's sake.
What this is is nothing more exotic than Winchester's Model 1897, pump action 12g shotgun. Military modifications were limited to adding a bayonet mount shortening the barrel (20") and adding a ventilated shroud to cover it, a line of protection from heat, the necessity of which will become apparent soon.
The gun itself was another piece of genius from our own John M. Browning, Mormon gun-designer par excel lance. With this gun, he produced what became the first commercially successful pump shotgun in history. Until supplanted by "hammerless" designs it remained in production until the 1950's. Furthermore, it remained as U. S. Military issue until after WW2.
The reason the barrel shroud was needed was due to the way these weapons were deployed. According to the Anoraks at the Great War Forum, shotgun teams comprised five men. Two shooters, two loaders and a fifth covering the rear with a rifle and bayonet. The brilliance of the shotgun in the application becomes clear when one remembers that, due to the kinks and traverses of a trench system - crucial for containing explosions and preventing someone from dropping in with a machine gun and cleaning everyone out - there was never a clear line of fire of more that twenty of thirty feet. Makes the infantry rifles with their impressive range sort of ridiculous.
In clearing an enemy trench, the technique the Brits had been using was one they called "blowing up the traverses". Essentially every corner encountered would be dealt with by tossing grenades over the top, then trying to time your arrival around the bend so you show up just after the explosion.
The American, shotgun technique was simply to hike on down the trench with the two shooters in the lead. The M1897 had no trigger disconnect so, if the trigger was held back, every action of the slide would fire a round. They would blaze away at all and sundry, passing the guns back for fresh ones when they'd exhausted their ammo (five rounds in the tube magazine and one in the chamber). As could be imagined, they'd heat up, hence the shroud.
The result of this quantity of OO buckshot (nine .32 caliber balls per load) was enough to give the Germans fits. They protested the use of such an ugly, inhumane weapon but to no avail. It's so much more civilized to machine gun folks from half a mile away but, you can't argue with success.
Anyway, the shotgun had arrived and so, in closing, two shots of the M1897 in action in the Second War. One with a Marine in the Pacific and another in the possession of an MP.