The United Defense M42, sometimes known as the Marlin for the company that did the actual manufacturing, was an American submachine gun used during World War II. It was produced from 1942 to 1943 by United Defense Supply Corp. for possible issue as a replacement for the Thompson submachine gun and was used by agents of the Office of Strategic Services (OSS). However, its usage was limited, and the Thompson continued to see service until the end of the war, alongside the M3 submachine gun, which was designed around the same time as the M42. History The M42 submachine gun was designed by Carl G. Swebilius of the High Standard Manufacturing Company in 1940. When High Standard was tasked with producing .50 Browning machine guns for the British government, further development of the submachine gun was handled the United Defense Supply Corporation founded by Pope and Jackson of the British Purchasing Commission. United Defense did not have any manufacturing capability so it contracted with Marlin Firearms to have the M42 actually built. The UD M42 was promoted as a replacement for the Thompson submachine gun, which the U.S. military considered both expensive and complicated to produce. Early model Thompson drum magazines were heavy and made a rattling sound when soldiers moved around with the weapon. Made in both 9×19mm Parabellum and .45 ACP prototypes, the 9 mm version was the only one to ever see widespread production. 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 25 9mm rounds in its magazine (designed by John E. Owsley, covered by patent 2,289,067). It has a cyclic rate of 700 rounds per minute. Frequently two 25-round magazines were welded face-to-face allowing a quick reload when the first became empty. However, just like using the Sten, resistance fighters were instructed to fire in short bursts when firing in full automatic to reduce the risk of overworking the weapon that would cause jamming and overall keeping it in a good condition. They were also strongly advised to keep the double magazine clear of grass, mud, dirt and any other debris out because of the risk of jamming. The weapon itself weighs (empty), with a length of . The barrel length is , and it has six-groove right-hand rifling. An extremely simple design, it was a straight blowback, selective