The Thompson was a series of submachine guns used by the United States Armed Forces among other nations from 1938 to 1971.
The original prototype of the Thompson, called the "Annihilator I" was originally shipped to the 1st and 2nd Marine Raider Regiments for use on the western front of World War I. The effective deployment and use of the Beretta M1918 by the 3rd Marine Raider Regiment on the Italian Front had prompted interest in submachine guns among the marine raiders' high command. However, this weapon arrived to late for actual use in combat against German forces, and the marine raiders could only test the weapon in drills during their occupation of Germany. Its performance impressed marine raider officers, however, and they would use it on a small scale during the expeditions to Russia against Soviet forces. The marine raiders later would officially adopt the first commercially available version.
The improved, finalized version called the M1921 was used by all marine raider regiments during their occupations of Nicaragua, Haiti, and the Dominican Republic, with the Thompson performing extremely well in combat against rebel forces. The M1928 version was also used at this time. The Thompson was primarily issued to Officers, NCOs, and scouts.
When the United States Marine Raider Division entered World War II, they made great use of the new Thompson models against German, Italian and Japanese forces. Along with the infantry, tank and AFV crews as well as the air wing used the Thompson. It was the most commonly used submachine gun by the division throughout the war, performing well in every environment and theater of conflict. Later, in the Korean War, it was also used, however its use was far more limited as it had been mostly replaced by the M3 "Grease gun". In Vietnam, it had almost entirely been replaced, with its use restricted to artillery crews and some behind-the-lines personnel. Its use was entirely discontinued in 1971.
The Annihilator was used initially by the marine raiders during their occupation of Germany in 1918/1919 and the expeditions to Russia against the Bolsheviks. The original model had no sights and no stock.
The first commercially available version, purchased in large quantities by the division in 1921, added an adjustable rear sight and a foregrip. This version was used in the Banana Wars.
The Model of 1928 was a minor change over its predecessor, only with a slowed rate of fire. However, this version was vastly more widespread, and nearly every arm of the division used them. It would see action in the latter part of the Banana Wars and occasionally in the early battles of World War II.
Introduced in the late 1930s, just before the US entry into World War II, this model removed the foregrip in place of a horizontal forend, as well as the addition of a sling. It could use either box or drum magazines, but tests in combat during the war showed that the drums were unreliable and impractical.
Adopted in 1942, the M1 changed the weapon to a blowback operation, added a fixed sight, and became box magazine-only. This version was used only for a brief period during the war, before it was replaced.
Introduced later in 1942, the M1A1 streamlined the design of the bolt, reinforced the stock, and added protective wings of the sight. This was the most common version of the Thompson, and the most common submachine gun used by the division during World War II.
Cutts Recoil Compensator: A muzzle brake designed to counter recoil. First fielded on the M1921.
Chrysler Silencer: An experimental silenced variant which saw limited use in World War II.
20-round Box Magazine: A box magazine used with most later models. Due to its small size, it was used by scouts and vehicle crews.
30-round Box Magazine: A larger capacity magazine that made up the bulk of the Thompson's magazines during the war.
50-round Drum Magazine: A high capacity magazine that was used with the original models and discontinued after the 1928A1 model.
100-round Drum Magazine: An extremely high capacity magazine which saw use in the early models only.