Why?
Because the nation's military expanded so much, so fast, they were DESPERATE for weapons- ANY weapons. The 'secondary' needs like guarding prisoners, securing supplies, guarding installations etc. could be met by shotguns. At that time there were thousands of commercial shotguns sitting in warehouses. Many of those shotguns were bought
en masse by the government, property stamped, and set up either as trench guns for front line use, as riot guns for secondary uses like guard duty, and some were used in training aerial gunners, and to provide R&R (recreation and relaxation) for servicemen in shooting skeet and trap.
When my dad (US Army Air Corps, went ashore on Operation Torch in North Africa) went through basic training, he said he learned the manual of arms with a chunk of 2X4. Does that help you understand how near run a thing WW2 was?
The US before World War Two ran what was called a cadre military, and that on a shoestring. The cadre concept was set up to expand as the need for more troops came about, but maintaining a large standing army was seen as too expensive. You might also remember that little economic bump in the road, known as The Great Depression. In 1930, US troop levels had shrunk to 256,000. Fifteen years later at the end of World War Two, the US had 12,123,000 servicemembers in uniform. That sort of expansion calls for a LOT of logistical support, including weapons.
Swearengen's book (linked in my post above, and referred to here often) gives some idea of the desperation behind the search for functional weapons in the early days of WW2. Anyone with any basic grasp of logistics knows you want weapons of the same type, so you only have to train in one manual of arms, have one set of spare parts, train one set of repair/support personnel, etc, right? Not when the wolf is nipping at your heels, you don't.
Pearl Harbor was a surprise to the population of the US, but WW2 had been spinning up for years in Europe (see
http://www.globalsecurity.org/military/ops/world_war_2.htm ). Desperate European nations were seeking war materiel anywhere they could find it, and some production orders were directed to US businesses. When the smoke cleared at Pearl Harbor, a lot of those orders were diverted for US use. Swearengen says:
Infantry weapons were in painfully short supply. This was especially true for those security detachments being embarked for overseas areas, as well as those guarding American coast lines and critical installations. Shotguns were called for, as they had been in World War I.
The War Department purchased riot-grade guns from all major American gun companies.
In addition, the shotguns still in inventory from World War One were put back into service. Remember Elmer Keith? He worked for the War Department during part of WW2, testing shotguns- see his book,
Shotguns by Keith (
http://www.osba.us/book/by+elmer+keith.aspx ) or his Wiki bio at
http://en.wikipedia.org/wiki/Elmer_Keith .
Canfield (also linked in my post above) says,
On July 1, 1940, it was determined that there were 21,187 military shotguns in the government's inventory. The majority of these were Winchester Model 1897 shotguns, but the number also included some Remington Model 10 and model 11 shotguns, along with some Winchester Model 12s. Many of the latter three types were in riot or training configuration, and the majority of the "combat shotguns" on hand in 1940 consisted of WWI-vintage Winchester Model 1897 trench guns.
Many tens of thousands of shotguns were added to these numbers during WW2, and shotguns were supplied as trench guns, riot guns, in sporting configuration for training and recreation, and a few were modified into aerial gunnery training platforms to train the gunners who protected heavy bombers. Fighting shotguns were produced by or procured from: Ithaca (Model 37), Remington (Model 11, Model 31, Sportsman ), Savage (Model 720), Stevens (520 and 620) and Winchester (Model 1897 and Model 12). How many? I'm not sure anyone knows exactly.
Shotguns had pretty much a 'backwater' role in WW2, they definitely weren't on center stage in the show. There were a good number of old-hand Marines in the Pacific who liked them, having had long experience with shotguns in the 'banana wars' and other small conflicts between WW1 and WW2. But even so, shotguns served to arm, train and even entertain thousands upon thousands of US servicemembers during the war.
fwiw,
lpl
I don't think there is any great mystery about using shotguns on guard duty at base camps and depots, Guard duty is at night, don't have to see the sights to shoot and they are intimating as hell. My under standing that out in the bad lands guard duty was preformed with what ever the duty weapons was. Shotguns were used only if they had them.
