United Defense M42

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).

History
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. 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(empty), with a length of 32.3 in. The barrel length is 11 in, 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.

Users

 * undefined
 * undefined
 * 🇮🇹 italy (1943–45)
 * 🇳🇱 netherlands
 * 🇵🇭 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
 * undefined 100 pieces from US supplies used by insurgent army and partisans during Slovak National Uprising