The Thompson also have a liken to American soldiers for it's fire rate and size, easy to carry around and fast to reload.
The Thompson M1921 and Thompson M1928 is very easy to compare, the M1921 version have a straight and retangular shape magazine, the M1928 version have a drum-shape like and it's a circular shape magazine.
But the Thompson SMG have many different madifications which can be added on to, there can be an extra handle to add on at the front and also a scope for a better aim rather then an iron sight.There were two type of millitary used Thompson SMG, one was the M1A1 (Also know as the M1) which have a retangular shape magazine. The other one was M1928A1 have a drum-shape like magazine but when it was first used, the sergeant who tested it was injured because of the first bullet jamed at the barrel, the trooper beside the sergeant saw no water splashed infront of them, he asked the sergeant but his answer was only "This is a new type of gun" when he fires the next round the second bullet hits the jammed one and creates an explosion, the sergeant was injured but the trooper was fine.
Then the U.S. marines used the M1928A1 type and went into the forest, the trooper only heard screams and Japanese rifle sounds and heard no U.S. Marine SMG sounds, when the Marines got out, they were in Rage that the gun was jammed and cursing about the gun.