The Thompson M1928A1 Thompson .45 ACP is a usa-made select-fire submachine gun chambered in .45 ACP, introduced in 1928. Primary use: military. Type: Submachine Gun Action: Select-Fire Caliber: .45 ACP Capacity: 30 Year introduced: 1928, USA Weight: 88 oz Overall length: 24" Status: Discontinued Military use: Yes Intended use: military