That's right. It's been known since 1939 from a Supreme Court case based on NFA34 that shotguns were never used in wartime.
The court said short barrelled shotguns weren't to their knowledge used in war, not shotguns in general... the WW1 trench gun wasn't short enough to be an NFA weapon. Shotguns were used in the military prior to WW1; I'm not aware of any that were sub 18 inches in barrel length, though I would not be surprised to find out that there were some. Do any of you know of any?
The military currently does use some shotguns with sub 18 inch barrels now, like the M26 Modular Accessory Shotgun System for door breaching.
