The Thompson was favored by soldiers, criminals and police alike for its ergonomics, compactness, large .45 ACP cartridge, reliability, and high volume of automatic fire. It has since gained popularity among civilian collectors for its historical significance.
The Thompson Submachine Gun was developed by General John T. Thompson who originally envisioned an auto rifle (semi-automatic rifle) to replace the bolt action service rifles then in use. While searching for a way to allow such a weapon to operate safely without the complexity of a recoil or gas operated mechanism, Thompson came across a patent issued to John Bell Blish in 1915 based on adhesion of inclined metal surfaces under pressure. Thompson found a financial backer, Thomas F. Ryan, and started the Auto-Ordnance Company in 1916 for the purpose of developing his auto rifle. The principal designers were Theodore H. Eickhoff, Oscar V. Payne, and George E. Goll. By late 1917, the limits of the Blish Principle were discovered: rather than working as a locked breech, it functioned as a friction-delayed blowback action. It was found that the only cartridge currently in U.S. service suitable for use with the lock was the .45 ACP round. Thompson then envisioned a "one-man, hand-held machine gun" in .45 ACP as a "trench broom" for use in the on-going trench warfare of World War I. Payne designed the gun itself and its stick and drum magazines. The project was then titled "Annihilator I", and by 1918, most of the design issues had been resolved. However, the war ended before prototypes could be shipped to Europe.
 Thompson intended the weapon as an automatic 'trench-broom' to sweep enemy troops from the trenches, filling a role for which the BAR had been proven ill-suited. Contemporaneously, this concept was developed by German troops using their own Bergmann MP18 submachine guns in concert with sturmtruppen tactics.
The Thompson first entered production as the M1921. It was available to civilians, though its high price resulted in few sales. (A Thompson M1921 with one Type XX 20 shot "stick" magazine was priced at $200.00 when a Ford automobile sold for $400.00.) M1921 Thompsons were sold in small quantities to the United States Marine Corps (despite the lore that the United States Postal Service-U.S. Post Office purchased this initial batch of 250 Colt Thompson Submachine Guns from the Auto-Ordnance Corporation to protect the mail from a spate of robberies, the AOC records and the USMC Quartermaster procurement records do not support this contention), followed by several police departments in the United States and minor international sales to various armies and constabulary forces, chiefly in Central and South America. . The Marines put their Thompson Submachine Guns to use in the Banana Wars and in China. It was popular with the Marines as a point-defense weapon for countering ambush by Nicaraguan guerrillas and led to the organisation of 4 man fire teams with as much firepower as a 9 man rifle squad. The major complaints against the Thompson were its weight, inaccuracy at ranges over 50 yards, and its lack of penetrating power, despite the powerful round it used.
Some of the first batches of Thompsons were bought in America by agents of the Irish Republic, notably Harry Boland. A total of 653 were purchased, but 495 were seized by US customs authorities in New York in June 1921. The remainder made their way to the Irish Republican Army by way of Liverpool and were used in the last month of the Irish War of Independence (1919–21). After a truce with the British in July 1921, the IRA imported more Thompsons and they were used in the subsequent Irish Civil War (1922–23). They were not found to be very effective in Ireland however. In only 32% of actions where it was used did the Thompson cause serious casualites (death or serious injury) to those attacked.
In 1928 Federal Laboratories took over distribution of the weapon from Thompson's Auto Ordnance Corporation. The cost at this time was US$225 per weapon, with $5 per 50 round drum and $3 for 20 round magazine.
In 1926 the Cutts Compensator (a recoil brake) was offered as an option for the M1921; Thompsons with the compensator were catalogued as No. 21AC at the original price of $200.00, with the plain M1921 designated No. 21A at a reduced price of $175.00.
Nationalist China also acquired a quantity for use against Japanese land forces, and eventually began producing copies of the Thompson in small quantities for use by its various armies and militias.
The Federal Bureau of Investigation first acquired Thompsons in 1933 following the Kansas City Massacre.
In 1938, the Thompson submachine gun was adopted by the U.S. military, serving during World War II and beyond.
There were two military types of Thompson SMG. The M1928A1 had provisions for box magazines and drums (the drums were disliked because of their tendency to rattle and jam). It had a Cutts compensator, cooling fins on the barrel, and its charging handle was on the top of the receiver. The M1 and M1A1 had a barrel without cooling fins, a simplified rear sight, provisions only for box magazines, and the charging handle was on the side of the receiver.
There were complaints from military users of the M1928A1 that the "L" fifty round drum magazine was heavy, noisy and slow to reload, and the "XX" twenty round box magazine was limited in capacity. Two alternatives were tested 6 December 1941 at Fort Knox: an extended thirty round box magazine and a forty round magazine made by welding two twenty round magazines face to face. Testers considered both superior to either the "XX" box or "L" drum. The thirty round box was approved as standard in December 1941 to replace the "XX" and "L" magazines. (The concept of welding two box magazines face-to-face was carried over with the UD 42 submachine gun.)
The staff of Savage Arms looked for ways to simplify the M1928A1, producing a prototype in Feb 1942 which was tested at Aberdeen Proving Ground Mar 1942; Army Ordnance approved adoption as the M1 in Apr 1942. M1s were made by Savage Arms and by Auto-Ordnance. M1s were issued with the thirty round box magazine and would accept the earlier twenty round box, but would not accept the drum magazine.
The Thompson was used in World War II in the hands of Allied troops as a weapon for scouts, non-commissioned officers (corporal, sergeant and higher ranking), and patrol leaders. In the European theater, the gun was widely utilized in British and Canadian Commando units, as well as the U.S. Army paratroopers and Ranger battalions who used it widely because of its high rate of fire, its stopping power and because it was very effective in close combat. A Swedish variant of the M1928A1, called Kulsprutepistol m/40 (meaning "submachine gun model 40"), served in the Swedish Army between 1940 and 1951. Through Lend-Lease, the Soviet Union also received the Thompson, but due to a shortage of appropriate ammunition in the Soviet Union, usage was not widespread.
In the Pacific Theater, Australian Army infantry and other Commonwealth forces initially used the Thompson extensively in jungle patrols and ambushes, where it was prized for its firepower, though its hefty weight of over 10 pounds and difficulties in supply eventually led to its replacement by other submachine guns such as the Owen and Austen. The U.S. Marines also used the Thompson as a limited-issue weapon, especially during their later island assaults. The Thompson was soon found to have limited effect in heavy jungle cover, where the low-velocity .45 bullet would not penetrate most small-diameter trees, or protective armor vests (in 1923, the Army had rejected the .45 Remington-Thompson, which had twice the energy of the .45ACP). In the U.S. Army, many Pacific War jungle patrols were originally equipped with Thompsons in the early phases of the New Guinea and Guadalcanal campaigns, but soon began employing the BAR in its place, especially at front (point) and rear (tail) positions, as a point defense weapon.
The M1928A1 variant entered mass production before the attack on Pearl Harbor, as on-hand stocks ran out. Changes included a horizontal forend, in place of the distinctive vertical foregrip ("pistol grip"), and a provision for a military sling. Despite new U.S. contracts for Lend-Lease shipments abroad to China, France, and the United Kingdom, as well as the needs of American armed forces, only two factories supplied M1928A1 Thompsons during the early years of World War II. Though it could use both the 50-round drum and the 20- or 30-round box magazines, active service showed the drums were more prone to jamming, rattled when moving, and were too heavy and bulky on long patrols. 562,511 were made. Wartime production variants had a fixed rear sight without the triangular sight guard wings and a non-ribbed barrel both like that found on the M1/M1A1.
In addition, the Soviet Union received M1928A1s, included as standard equipment with the M3 light tanks obtained through Lend-Lease. The weapons were never issued to the Red Army, however, because of a lack of .45 ACP ammunition on the Eastern Front, and were simply put in storage. As of September 2006, limited numbers of these weapons have been re-imported from Russia to the United States as disassembled "spare parts kits", the entire weapon less the receiver (as required by Federal law).
M1 Carbine. This platform was based on the M1921/27 variants and worked well but due to the war effort was found expensive for mass production and defied the concept of a Light Rifle. However it did form the basis of the Thompson Light Rifle, a development of this variant with a barrel shroud which housed a quick barrel change device similar to the MG42 but was refused in favour of the mentioned M1 Carbine.
Answering the call for further simplification, the M1 was standardized in April 1942 as the United States Submachine Gun, Cal. .45, M1. Rate of fire was reduced to approximately 600-700 rpm. First issued in 1943, the M1 utilized a simple blowback operation, the charging handle was moved to the side, and the flip-up adjustable Lyman rear sight was replaced with a fixed L sight. Late M1 Thompsons had the triangular rear sight guard wings added to the L sight which was standardized on the M1A1 version. The slots adjoining the magazine well allowing use of the drum magazine were removed. The less expensive and more-easily manufactured "stick" magazines were used exclusively in the M1, with a new 30-round version joining the familiar 20-round type. The Cutts compensator, barrel cooling fins, and Blish lock were omitted while the buttstock was permanently affixed.
M3 (commonly called "Grease Gun").
The Model 1927A1 is a semi-automatic only version of the Thompson, originally produced by Auto-Ordnance of West Hurley, New York for the civilian collector's market from 1974 to 1999. It has been produced since 1999 by Kahr Arms of Worcester, Massachusetts. It is officially known as the "Thompson Semi-Automatic Carbine, Model of 1927A1." The internal design is completely different to operate from the closed bolt and the carbine has barrel length of 16.5 inches (versus open bolt operation and barrel length of 10.5 inches for the full automatic versions). Under federal regulations, these changes make the Model 1927A1 legally a rifle and remove it from the federal registry requirements of the National Firearms Act. These modern versions should not be confused with the original semi-automatic Model of 1927 which was a slightly modified Model of 1921 produced by Colt for Auto-Ordnance.
The Model 1927A1 is the semi-automatic replica of the Thompson Models of 1921 and 1927. The "Thompson Commando" is a semi-automatic replica of the M1928A1. The Auto-Ordnance replica of the Thompson M1 and M1A1 is known as the TM1, and may be found marked "Thompson Semi-Automatic Carbine, Caliber .45M1".
The Model 1927A3 is a semi-automatic, .22 caliber version of the Thompson produced by Auto-Ordnance in West Hurley.
The Model 1927A5 is a semi-automatic pistol version, .45ACP version of the Thompson originally produced by Auto-Ordnance in West Hurley. It featured an aluminum receiver to reduce weight. It has been produced since 2008 by Kahr Arms of Worcester, Massachusetts as the "M1927A1 TA5".
The perceived popularity of submachine guns such as the Thompson with violent gangsters in the 1920s and 1930s was one of the main reasons given for passage of the National Firearms Act by the United States Congress in 1934. One of its provisions is that all owners of any fully-automatic firearm were required to register them with the predecessor agency of the modern Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). The law also placed restrictions on the possession, transfer, and transport of the weapons.
automatic and semi-automatic variants, copies, or replicas. The semi-automatic versions are less regulated by federal law.Thompson submachine guns (including all variants or modified versions) are classified as Prohibited Weapons in Canada. Consequently, they cannot be legally imported or owned except under very limited circumstances. For example, to own one it must be "grandfathered" from before the bill was passed against it.
By the time of the Korean War, the Thompson had seen much use by the U.S. and South Korean Military, even though Thompson had have been replaced as standard issue by the M3 and M3A1. Production of the Thompson was over 1.7 million, of the M3 and M3A1 688,975, and the Thompson models remained classed as Limited Standard or Substitute Standard long after the standardization of the M3/M3A1. Many Thompsons were distributed to Chinese armed forces as military aid before the fall of Chiang Kai-Shek's government to Mao Zedong's Communist forces in 1949. During the Korean War, American troops were surprised to encounter Chinese Communist troops heavily armed with Thompsons, especially during surprise night assaults. The gun's ability to deliver large quantities of short-range automatic assault fire proved very useful in both defense and assault during the early part of the conflict. Many of these weapons were captured and placed into service with American soldiers and Marines for the balance of the war.
During the Vietnam War, some South Vietnamese army units and defense militia were armed with Thompson submachine guns, and a few of these weapons were used by reconnaissance units, advisors, and other American troops. It was later replaced by the M16. Not only did some U.S. soldiers have use of them in Vietnam, but they encountered it as well. The Vietcong liked the weapon, and used both captured models as well as manufacturing their own copies in small jungle workshops.
In the conflict in Northern Ireland, known as 'The Troubles' (1969–1998), the Thompson was again used by the Irish Republican paramilitiaries. According to historian Peter Hart, "The Thompson remained a key part of both the Official IRA and Provisional IRA arsenals until well into the 1970s when it was superseded by the Armalite and the AK-47" 
The Thompson was also used by U.S. and overseas law enforcement and police forces, most prominently by the FBI. The FBI used Thompsons until 1976, when it was declared obsolete. All Thompsons in U.S. government possession were destroyed, except for a few token museum pieces and training models.
The Thompson, or copies of the gun, are still seen from time to time in modern day conflicts, such as the Bosnian War.
Early versions of the Thompson had a fairly high cyclic rate of fire, as high as 1,200 rounds per minute, with most police Model 1921 at 850 and military Model 1928 at 720. Later M1 and M1A1 Thompsons averaged 600 rpm. This rate of fire, combined with a rather heavy trigger pull and a stock with excessive drop, increases the tendency of the gun to climb off target in automatic fire. Compared to modern 9mm submachine guns, the .45 Thompson is quite heavy. This was one of the major complaints against the weapon made by servicemembers of militaries that issued the Thompson.
Although the drum magazine provided significant firepower, in military service it was found to be overly heavy and bulky, especially when slung on patrol or on the march. It was also rather fragile, and cartridges tended to rattle back and forth inside it, producing unwanted noise. For these reasons, the 20-round and later 30-round box magazines soon proved most popular with military users of the M1928A1, and drum compatibility was not included in the design of the wartime M1 and M1A1 models. The Thompson was one of the earliest submachine guns to incorporate a double-column, double-feed box magazine design, which undoubtedly contributed to the gun's reputation for reliability. In addition, the gun performed better than most after exposure to rain, dirt, and mud.
The select fire (semi- or full automatic) Thompson fires from the "open bolt" position, in which the bolt is held fully to rearward by the sear when cocked. When the trigger is depressed, the bolt is released traveling forcefully forward to chamber and simultaneously fire the first and subsequent rounds until either the trigger is released or the ammunition is exhausted.
US$25,000 or more. For WWII, approximately 1,700,000 Thompson Submachine Guns were produced by Auto-Ordnance and Savage Arms, with 1,387,134 being the simplified World War II M1 and M1A1 variants (without the Blish lock and oiling system). Post WWII, Numrich Arms acquired Auto-Ordnance and resumed small scale production of both full automatic and semi-automatic only versions at West Hurly. Semi-automatic only versions configured as civilian-legal rifles are currently produced by Auto-Ordnance Company, a division of Kahr Arms, for the collector market at prices ($900.00 to $1400.00) considerably lower than the prices for originals.
There were two main experimental models of the Thompson. The Persuader was a belt-fed version developed in 1918, and the Annihilator was fed from a 20 or 30-round box magazine, which was an improved model developed in 1918 and 1919. Additionally, the 50- and 100-round drum magazines were developed.
The Model 1919 was limited to about 40 units, with many variations noted throughout. The weapons had very high cyclic rates around 1,500 rpm. This was the weapon Brigadier General Thompson demonstrated at Camp Perry in 1920. Almost all Model of 1919s were made without buttstocks and front sights, and the final version closely resembled the later Model of 1921. The New York City Police Department was the largest purchaser of the Model of 1919. This model was designed as an automatic Colt .45 to "sweep" trenches with bullets. Some experimental calibers were .45 ACP (11.4x23mm), .22LR, .32 ACP, .38 ACP, and 9mmP. wood furniture and finely-machined parts. The M1921 was famous throughout its career with police and criminals and in motion pictures. This model gained fame from its' use by criminals during Prohibition, and was nicknamed "tommy gun" by the media.
U.S. Army. It fired the more powerful .45 Remington-Thompson cartridge from a 14-inch (35.5 cm) barrel, with greater range than the .45 ACP. It introduced a horizontal forearm, sling, bipod and bayonet lug. The M1923 was intended to fill the same role of the M1918 Browning Automatic Rifle (BAR) which the Army was already satisfied with, and did not give the Model of 1923 much consideration, so it was not adopted.In an attempt to expand interest and sales overseas, Auto-Ordnance partnered with and licensed Birmingham Small Arms Company (BSA) in England to produce a European model. These were produced in small quantities and have a different appearance than the classic style. The BSA 1926 was manufactured in 9 mm and 7.63 Mauser calibre and were tested by various governments, including France in the mid 1920s. It was never adopted by any military force, and only a small number were produced.The Model 1927 was the open bolt semi-automatic-only version of the M1921. It was made by modifying an existing Model 1921, including replacing certain parts. The "Thompson Submachine Gun" inscription was machined over to replace it with "Thompson Semi-Automatic Carbine", and the "Model 1921" inscription was also machined over to replace it with "Model 1927." Although the Model 1927 was semi-automatic only, it was easily converted to fully automatic by installing a full-auto Model 1921 fire control group (internal parts). Most Model 1927s owned by police have been converted back to full-auto. The original Model 1927 is classified as a machine gun under the National Firearms Act of 1934 (a) by being "readily convertible" by swapping parts and (b) by a 1982 BATF ruling making all open bolt semi-automatic firearms manufactured after the date of this ruling classified as machineguns.
The Model 1928 was the first type widely used by military forces, with the U.S. Navy and U.S. Marine Corps as major buyers through the 1930s. The original Model 1928s were Model 1921s with weight added to the actuator, which slowed down the cyclic rate of fire, a U.S. Navy requirement. The Navy Model 1928 has several names by collectors today they are; the 'Colt Overstamp', 'The 1921 Overstamp', '28 Navy', or just '28N'. The "overstamp" term refers to the '1' in '1921' being stamped over with an '8'. The 1928 Thompson would be the last small arm adopted by the U.S. Army that used a year designation in the official nomenclature. With the start of World War II, major contracts from several countries saved the manufacturer from bankruptcy.