United Defense M42

The M42 began as a design Carl G. Swebilius drew up at the High Standard Manufacturing Company in 1940. When High Standard was assigned to building .50 calibre machine guns for Britain instead, further work on the submachine gun passed to a new company, United Defense Supply Corporation, set up by two members of the British Purchasing Commission. United Defense had no factory of its own and contracted the Marlin Firearms Company to actually build the weapon, which is why collectors and period sources often call it simply “the Marlin” rather than by its official designation.

It is a straightforward straight-blowback, selective-fire design, built with entirely machined rather than stamped parts. This was a choice that made it accurate and easy to maintain in testing but expensive and slow to produce under wartime conditions, exactly the problem it was meant to solve for the U.S. military, which considered the Thompson too costly and complicated. Only around 15,000 of the production 9×19mm version were built between 1942 and 1943, alongside six hand-made .45 ACP prototypes that used a larger 25-round magazine; the standard production gun instead used a 20-round magazine, often welded in facing pairs for a fast reload, a method later called “jungle style.”

Despite War Department interest, licensing and royalty complications limited production, and the M42 was formally classified only as a substitute standard once the cheaper, stamped-steel M3 submachine gun arrived. It found more use outside American ranks than within them: air-dropped to resistance forces across occupied Europe, including on Crete and in Italy, Belgium, the Netherlands, Denmark, Norway and France, and supplied in quantity to Dai Li’s forces in China against Japanese occupation, later passing in part to Communist Chinese units during the civil war that followed. Its 9mm chambering let European resistance fighters reload with captured German ammunition, reducing their dependence on further airdrops.

No maker specification sheet independent of Wikipedia’s own uncited figures was found for this page’s mass, length, barrel length or cyclic rate; Wikipedia’s own infobox and article body disagree on the cyclic rate, and both figures are recorded here as estimated rather than verified. No rifling twist rate or sight radius is published.