2. The M50 Reising Machine Gun
Adopted by the Marine Corps during WWII, this submachine gun was intended to complement the Thompson, since the latter model couldn’t be manufactured in sufficient numbers. And despite being cheaper to make and lighter to hold, the Reising wasn’t as efficient as it appeared on paper.
Sadly, it was very ill-equipped for the environment the Marines were generally located in. Sand would jam in the gun, and would then be hard to disassemble and clean.
Parts weren’t interchangeable either, as each was handmade for its individual model, so many soldiers had to clean their weapons at the same time just so they had a working firearm to use at all. In fact, the Marines were so upset with the M50 Reising guns that there is documentation recounting how troops threw their firearms into a river in protest.