Those are M-3 “Grease Gun” submachine guns. Fired a .45ACP cartridge. They had barrels that would allow them to fire 9x19 rounds in some cases.
They were produced to bring down the cost of sub-guns, because the Thompson “tommy gun” was (and still is) a very expensive, exquisitely machined piece of work. Those are mostly sheet metal stampings.
Barrels were steel tubing w/o rifling, just a plane old smooth bore firing a big chunk of lead.
PS War time production brought the straight blow back (no Blish lock mechanism) Thompson down to about $78/each, the M3 was $11/each.