Thompson came across a patent issued to the American inventor John Bell Blish in 1915, while searching for a way to allow his weapon to operate safely without the complexity of a recoil or gas-operated reloading mechanism.

[36] At an Auto-Ordnance board meeting in 1919, in order to discuss the marketing of the "Annihilator", with the war now over the weapon was officially renamed the "Thompson Submachine Gun".

By the time of the Battle of Blair Mountain, 37 had been acquired by the West Virginia state police and 56 were in the hands of coal companies and local law enforcement.

The first test of the Thompson in Ireland was performed by Irish Republican Army unit commander Tom Barry, of the West Cork Brigade, in the presence of IRA leader Michael Collins.

[45][46] Around 200 Model of 1921 Thompsons were sold in 1926 to the United States Postal Inspection Service[47][27][48][failed verification] so they could protect the mail from a spate of robberies.

[49] These weapons were loaned to the United States Marine Corps which was, at that time, tasked with guarding mail shipments; this prompted the US Navy to formally test the Thompson.

[27] The Thompson saw popularity as a point-defense weapon for countering ambushes by Nicaraguan guerrillas (in the Banana Wars) and led to the creation of four-man fire teams which had as much firepower as a nine-man rifle squad.

[52] Thompsons had also been widely used throughout China, where several Chinese warlords and their military factions running various parts of the fragmented country made purchases of the weapon, and subsequently produced many local copies.

In the 1930s, Taiyuan Arsenal (a Chinese weapons manufacturer) produced copies of the Thompson for Yan Xishan, the then warlord of Shanxi province.

The staff of Savage Arms looked for ways to simplify the M1928A1, and produced a prototype in February 1942, which was tested at Aberdeen Proving Ground in March 1942.

In the European theater, the gun was widely utilized in British and Canadian commando units, as well as in the U.S. Army paratrooper and Ranger battalions, where it was issued more frequently than in line infantry units because of its high rate of fire and its stopping power, which made it very effective in the kinds of close combat these special operations troops were expected to undertake.

However, the weight of the ammunition and difficulties in supply eventually led to its replacement in Australian Army units in 1943 by Australian-made submachine guns, the Owen and Austen.

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.

)[61] 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 Browning Automatic Rifle in its place as a point defense weapon.

[62] The Army introduced the U.S. M3 and M3A1 submachine guns in 1943 with plans to produce the latter in numbers sufficient to cancel future orders for the Thompson, while gradually withdrawing it from first-line service.

Though the M3 was considerably cheaper to produce, at the end of World War II, the Thompson, with a total wartime production of over 1.5 million, outnumbered the M3/M3A1 submachine guns in service by nearly three to one.

The opposing Communist fighters of the Democratic Army of Greece were also using Thompson submachine guns, either captured from government forces or inherited from ELAS.

[71] 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[72]).

A Model 1921A believed to have been owned by Bonnie and Clyde, but without historical documentation to substantiate this provenance, sold at auction on 21 January 2012, in Kansas City for $130,000.

[74] Compared to more modern submachine guns, the Thompson is quite heavy, weighing roughly the same as the contemporary M1 Garand semi-automatic rifle, and requires a lot of cleaning.

[39] Although the drum magazine provided significant firepower, in military service it was found to be overly heavy and bulky, especially when slung on the shoulder while marching.

[76] 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 1928 variant can be disassembled easily by first detaching the stock, then sliding off the lower receiver and then simply removing the internal parts, cleaning them, and then putting it back together.

In its original design, it was finished more like a sporting weapon, with an adjustable rear sight, a blued, finned barrel and vertical foregrip (or pistol grip) and the Blish lock.

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.

The Model 1927A1 is a semi-automatic replica version of the Thompson, originally produced by Auto-Ordnance of West Hurley, New York for the civilian collector's market from 1974 to 1999.

The Model 1927A5 is a semi-automatic, .45 ACP pistol version of the Thompson originally produced by Auto-Ordnance in West Hurley from the 1970s until the late 1980s or early 1990s.

In an attempt to expand interest and sales overseas, Auto-Ordnance entered into a partnership with and licensed the Birmingham Small Arms Company Limited (BSA) in England to produce a European model.

[94]: Part 1.86 [95] 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.

It is now effectively impossible for a firearm of this type to be legally possessed by a member of the general public, except in certified deactivated condition or where specifically manufactured as a semi-automatic in caliber .22LR.