Short answers, pulled from the story.
The first recorded use of the term shotgun was in 1776, in correspondence to and from Fort Boonesborough in Kentucky. The correspondence is held in the Lyman Draper Collection at the University of Wisconsin.
Daniel Myron LeFever is credited with inventing the American hammerless shotgun. Working for Barber & LeFever in Syracuse, New York, he introduced his first hammerless design in 1878 and patented the first truly automatic hammerless shotgun in 1883.
Germany filed a formal diplomatic protest against American shotgun use on the Western Front in 1917, alleging the weapons violated the laws of warfare. The judge advocate general rejected the protest because Germany objected to the use of lead shot, which would have been illegal, but military shot was plated. It is the only time the legality of the shotgun in warfare has been formally challenged.
The 12-gauge is by far the most common shotgun gauge. Its bore diameter is 0.729 inches, or 18.5 mm. The 20-gauge, with a bore of 0.614 inches, is the second most common.
John Browning patented the Auto-5, America's first semi-automatic shotgun, in 1900. First produced by Fabrique Nationale beginning in 1902, it remained in production until 1998, a span of roughly 96 years.
In conflicts including the Russia-Ukraine war, shotguns have proven effective at shooting down fast-moving enemy drones. The spread of pellet-based rounds such as buckshot and birdshot makes it easier to hit small, fast targets compared to firearms that fire a single projectile.