Article on use of shotguns in war
Here's a pdf file from Army Lawyer, on the legalities of use of shotguns in war. It mentions the German WWI protest over use of the Winchester 1897, and threats to execute any soldier captured with one, and the American response (which after arguing legalities said the US would retaliate against their troops if they tried -- those were days when the game was played for keeps).
I found the historical discussion of use of shotguns equally interesting. And the note that in jungle fighting in Malaysia, the British found that at 30 yards, the shotgun was twice as likely to get a hit as a rifle, and I gather substantially more likely to get a hit than a submachine gun.