Thompson M1 The Thompson M1A1 was the main American submachine gun of the World War II and Operated until 1971 under U . S Military . History . John T . Thompson founded the Auto Ordnance Corp . in 1916 , and began his developments in submachine guns with purchase of John Blish patent ( 1915 ) , that described a delayed blowback automatic firearm . This patent described delayed blowback breech system in which a sloping metal wedge interlocked the breech block with the gun body . Under high pressure , as when the cartridge fired , the angle of the slope was such that the mating faces jammed solid . As the pressure dropped , the faces were able to slip across each other , the wedge moved up due to the slope , and the breech unlocked . This idea was used in all Thompson submachine guns except for M1 and M1A1 ( those were simply blowback operated ) . The first Thompson experimental submachine gun appeared in 1919 , and first production model appeared in 1921 ; it was manufactured under contract by Colt Firearms Manufacturing Co , as well as later M1928 models . Production of M1928A1 and M1 submachine guns was carried out by Auto - Ordnance and Savage , and some licensed copies were manufactured by B . S . A . in Great Britain . There also were some submachine guns that never reached full - scale production , such as " Military model " M1923 , which was developed with intent to extend the effective range out to 600 yards ( approx 550 meters ) . To achieve this goal , M1923 was chambered for a special . 45 Remington - Thompson ammunition , which fired heavier 250 - grain ( 16 , 2 gram ) bullet ( as opposed to standard 230 - grain . 45ACP bullet ) at higher muzzle velocities of about 1450 fps ( 440 m / s ) . This weapon also had longer barrel , and optional bipod and bayonet mount . It was tested but never produced in any significant numbers . The other rare version was the " original " Model 1927 , which was a semi - automatic only version of Model 1921 . The first Thompson gun to see some military use was Model 1928 , used by US navy during its expedition in Nicaragua . The so - called " Navy " model 1928 was distinguished by a horizontal forearm that replaced the front grip , and by added sling swivels . With the start of World war 2 , US Army procured a large number of Model 1928 submachine guns in " Navy " configuration , marked as US Model 1928A1 . These weapons were rather expensive to make , and in 1942 Army adopted a simplified version of M1928A1 , known as M1 . A little later , an M1A1 version was adopted , which further simplified the design by adoption of a fixed firing pi ; otherwise M1A1 were similar to M1 submachine guns . Thomson submachine guns served in US Army well into the Vietnam era , although in limited numbers . American police used Thompson guns until 1970s or 1980s , and few still could be found in some police armories in USA and several other countries of the world . Thompson submachine guns were widely exported commercially prior to and after WW2 ; Many guns were supplied to Britain and USSR through Lend - lease program during WW2 . It must be noted that Soviet troops generally not liked Tommy guns , because of excessive weight and lack of bullet penetration , compared to 7 , 62mm submachine guns such as PPSh - 41 or PPS - 43 . Thompson M1921 and M1928 submachine guns were delayed blowback operated , selective fired weapons , based on Blish principle . Blish patent described a delayed blowback breech system in which a sloping metal wedge interlocked the breech block with the gun body . Under high pressure , as when the cartridge fired , the angle of the slope was such that the mating faces jammed solid . As the pressure dropped , the faces were able to slip across each other , the wedge moved up due to the slope , and the breech unlocked . The wartime M1 and M1A1 submachine guns used simple blowback action . All Thompson submachine guns fired from open bolt . The cocking handle was located on the top of receiver on Models of 1921 and 1928 , ad on the right side of the receiver on models M1 and M1A1 . Separate manual safety and fire mode selector levers were located on the left side of receiver , above the trigger . Barrel was usually partially finned , and on model 1928 , fitted with so - called Cutts compensator ( not present on M1 and M1A1 ) . Feed was from double - row box magazines containing 20 or 30 rounds , or drum magazines holding 50 or 100 rounds . Box magazines were inserted into the magazine slot from below ; drum magazines were inserted into the same slot from the side . Drum magazines were not available for M1 and M1A1 submachine guns . Furniture included pistol grip , detachable wooden shoulder stock and either a detachable forward grip or a horizontal forearm . Sights on pre - war models included front blade and protected rear , which combined a fixed open - notch blade and raising diopter , which was adjustable for both windage and range ( up to 500 yards ) . Wartime models ( M1928A1 , M1 and M1A1 ) used a simple fixed aperture ( diopter ) rear sight , with or without protecting side " ears " . At the present time , Kahr Arms makes a variety of " Tommy - guns " under Auto Ordnance trade mark . These weapons are limited to semi - automatic fire only and usually have longer barrel to conform to US laws