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United Defense M42
United Defence M42.jpg
UD M42 submachine gun
Type Submachine gun
Place of origin United States
Service history
In service 1942-1945
Used by See Users
Wars World War II
Production history
Designer Turner
Manufacturer United Defense Supply Corp.
Produced 1942–1943
Number built 15,000
Variants M42 submachine gun
Turner Carbine
Weight 10 lbs., (4.1 kg)
Length 32.3 in. (820 mm)
Barrel length 11 in. (279 mm)

Caliber 9x19mm Parabellum
.30 Carbine (Turner Carbine)
.45 ACP (Prototype model)
Action Blowback
Rate of fire 700 rpm
Muzzle velocity 1,100 ft/s (335.3 m/s)
Feed system 20 rounds box magazine
Sights fixed front post, rear adjustable for windage

The United Defense M42 was an American submachine gun in World War II. It was produced from 1942 to 1943 by United Defense Supply Corp. (a government-formed company specifically tasked with weapons development) for possible issue as a replacement for the Thompson submachine gun and was used by agents of the Office of Strategic Services (OSS).[1]


The M42 was developed by United Defense Supply Corp. specifically as a replacement for the Thompson submachine gun, which the U.S. military considered both expensive and complicated to produce. Made in both 9x19mm Parabellum and .45 ACP prototypes, the 9 mm version was the only one to ever see widespread production. Manufactured by High Standard Firearms and Marlin Firearms, about 15,000 were produced in the last three years of World War II.[2] Only six .45 ACP prototype test guns were made.

The weapon holds 20 9mm rounds in its magazine, and can fire them at 700 rounds per minute. Frequently two 20 round magazines were welded face-to-face allowing a quick reload when the first became empty (see illustration). The weapon itself weighs 10 lb (4.54 kg)(empty), with a length of 32.3 in (820 mm). The barrel length is 11 in (279 mm), and it has six-groove right-hand rifling.

An extremely simple design, it was a straight blowback, selective fire weapon. It was built under "hurry-up" war conditions and some of its design flaws stem from this approach. Problems with the weapon were varied. Under combat conditions it was found that the sheet metal magazines had a tendency to warp out of shape causing feeding problems. They had little tolerance for exposure to large amounts of mud and sand and tended to jam if not cleaned regularly. The gun was also labor intensive to produce. It used all machined parts, no stampings, and under wartime conditions machine work is at a premium.

The M42 submachine gun was classified as a substitute standard when the M3 submachine gun was introduced.

Operational use

Intended for use by U.S. troops at the time of its design, it found more favor being air-dropped to partisan forces in occupied Europe. The weapon was air dropped to supply British-led partisan forces on the island of Crete, where it was used extensively. It also saw use among the partisan forces of the Italian and French Resistance. Some of them were transferred to Dai Li's regular resistance forces in China for use against the Japanese invasion. The United Defense M42 for use by Filipino troops under the Philippine Army and Philippine Constabulary from 1942 through until the 1960s during World War II under the Japanese Occupation and Post-World War II era and used again by the local recognized guerrillas from 1942 to 1945 during the Japanese Occupation. The use of the 9 mm caliber allowed resistance forces to use captured ammunition in their weapons, eliminating the need for repeated re-supply drops.

Overall the weapon failed in its intended role (to replace the Thompson) but proved effective in limited use in the hands of resistance forces.


  •  Taiwan[3]
  •  China[3]
  •  Italy (1943–45)
  •  Netherlands[3]
  •  Philippines used by the Philippine Army and Constabulary during World War II and Post War era from 1942 to 1960s and using again by the local recognized guerrillas from 1942 to 1945 during World War II.
  •  United States[3]
  •  Czechoslovakia 100 pieces from US supplies used by insurgent army and partisans during Slovak National Uprising

See also


  • Nelson, Thomas B. (1963). The World's Submachine Guns, Volume I. International Small Arms Publishers.
  • Iannamico, Frank. (2004). United States Submachine Guns: From the American 180 to the ZX-7. Moose Lake Publishing. ISBN 0-9742724-0-X.

  1. Bishop, Chris (1998). The Encyclopedia of Weapons of World War II. New York: Orbis Publiishing Ltd. ISBN 0-7607-1022-8 .
  2. Canfield, Bruce N. (2006). "M42 UD (United Defense) Submachine Gun". National Rifle Association. pp. 26&27. 
  3. 3.0 3.1 3.2 3.3 McNab, Chris (2002). 20th Century Military Uniforms (2nd ed.). Kent: Grange Books. ISBN 1-84013-476-3. 

External links

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