U.S. v. Miller loosely established the test (later solidified in 2008's Heller v DC) that weapons commonly used in militia service are inherently deserving of second amendment protections.
Miller, a known mobster who was caught with a sawed off shotgun lost his case because
a) the military testified that they had never used sawed off shotguns, so they were not useful to a military, ergo a militia (which was a lie -- they had used them, and found them useful for trench-clearing)
b) Miller's attorney was not very good, and didn't even challenge that testimony, much less so by totally disproving it -- I offer a little sympathy here as they didn't have Google at the time
Also noteworthy, Miller was actually dead when the decision came down, as he'd been murdered, and because /shrug, the trial kept going, but the defense (for obvious reasons) quit trying. He was sentenced in absentia.
Which I find just insane. People say no one wants to take Americans guns rights away, but we were literally one vote from effectively doing so.
https://www.cbsnews.com/news/illinois-town-votes-to-ban-assa...
I'd rather have a new amendment then have judges be able to decide what the definition of arms is. Slippery slope. They really could one day decide that 'arms' is only muskets, or even just knives.