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M1A1 .45 Caliber Thompson Submachine Gun and Manual

The Caliber .45 M1A1 Thompson utilized a simple blow-back system of operation, with fully and semi-automatic operation, 20-and 30-round detachable box magazines, a 600 rpm rate of fire with 432 ft-lb muzzle energy and an effective range of 50 yards. More reliable than most submachine guns in field conditions of dirt and rain, etc, it was considered heavy and with a low-velocity round of limited penetrating power.


TM 9-1215: Thompson Submachine Gun Technical and Maintenance Manual

TM9-2200: Technical Manual for WWII Small Arms

Ammo Data Sheets for Small Arms


M1A1 Thompson Submachine Gun with 30 Round Magazine

M1A1 Thompson Submachine Gun with 30 Round Magazine

Unofficial Tommy Gun Page


Operation Selective fire (fully and semi-automatic)
Caliber .45 (11.4 mm)
Muzzle velocity 280 mps (920 fps), 432 ft-lb muzzle energy
Ammunition .45 ACP, 230 gr bullet, 5 gr charge
Capacity Thompson (M1928A1): 50-round drum & 20- and 30-round detachable box magazine.
M1 and M1A1: 20-and 30-round detachable box magazine
Weight 4.9 kg (11 lbs)
Overall length 85.6 cm (33.7 in)
Rate of fire 600 to 725 rpm
Effective range 50m (55yds)

Although officially replaced with the M3A1, Thompsons were sometimes used during the Korean war. The M1 carbine was intended to replace the submachine gun in service, and its greater range and penetrating power were distinct advantages. At close quarters, however, the Thompson was superior.

The Chinese began the Korean war armed primarily with Japanese, US, British and Chinese Nationalist weapons. Russian, and home-made Russian model weapons became dominant only as the KW progressed. In their attack on the Marines in Chosin, the Thompson Submachine gun was one of the weapons they used.

At the start of the Korean War, apart from grenades, a Chinese regiment of 3,000 men typically had only 1,000 to 1400 weapons of all types. They soon began purchasing weapons from the USSR, as well as deploying weapons they captured from us, and by mid 1951 showed no shortage of infantry weapons. Throughout the KW, the Chinese sent platoons into action armed primarily with stick hand grenades, being expected to further arm themselves with weapons found on the field of battle. Other assault platoons with them had SMGs firing pistol cartridges.

These assaults were so effective in the first six month of fighting primarily because probes, feints and Reconnaissance beforehand usually located our primary defenses and weaknesses. Their attacks then tried to fix us in position while other units encircled our forward units and blocked our lines of supply and communication.

The effectiveness of assaults with such weapons, concentrated with great violence where most effective, on troops who had reason to think they might be cut-off and destroyed in isolation, was considerable.

As our forces grew familiar with the CCF tactics, and increased in our own confidence and tactical skill against such attacks, our superior fire-power and air supremacy enabled us to drive them back until Truman ordered us to cease attacks to gain ground once we had essentially reached the 38th parallel.

At this point, diplomacy became the main UN tool.

As usual, the infantry paid for these gentlemanly talks with ungentlemanly battles, blood and suffering.


John T. Thompson who helped develop the M1903 Springfield rifle and M1911 .45 caliber pistol, began work on a "trench broom" for close quarter combat shortly after his retirement from the Army in 1918. He recognized that the .45 caliber slug used in the M1911 pistol would be devastating when used in a fully automatic weapon.

By the spring of 1920 Thompson's company (Auto-Ordnance) produced a prototype capable of firing 800 rounds a minute.


Thompson submachine gun
Thompson Submachine Gun "Tommy Gun"

Despite its excellent test performance, the Thompson was not adopted for use by either the US Army or Marine Corps. Still, Thompson contracted with Colt for the manufacture of 15,000 guns, designated "Thompson Submachine Gun, Model of 1921". The 15,000 guns manufactured by Colt lasted until the eve of World War II. In 1940, the U.S. Army ordered 20,000 Thompson submachine guns; in 1941 the Army ordered an additional 319,000.



One of the main assets of the Thompson submachine gun was reliability; it performed better than most submachine guns when exposed to dirt, mud and rain.

The main complaints against the Thompson were it's weight, inaccuracy at ranges over 50 yards, and lack of penetrating power.


Bulletin Board comment by Norsky, NorskyV@aol.com
September 21, 2000

The Thompson M1A1 submachine gun did not accept the 50-round drum magazine as your web site indicates.


BK: This fact was already noted in the above specifications.

In 1942 the original Thompson M1928 which had the cocking knob on top of the receiver and utilized the Blish Lock system of operation was redesigned as the Thompson M1A1.

The M1A1 utilized a simple blow-back system of operation and the bolt handle was moved to the side. To save manufacturing expense, other features were downgraded or eliminated, including the Cutts compensator, the finned barrel, the fingered fore-grip, and the flip-up adjustable rear-sight. The M1A1 did not accept the drum magazine - it was abandoned for various reasons, including the fact that the contents slid back and forth and made noise on night patrols (See JANE'S Guns Recognition Guide, pgs. 290 & 291). KAHR ARMS now currently manufactures Thompson firearms. www.kahr.com or www.auto-ordnance.com


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