Originally designed by Carl Swebilius of High Standard, the M42 was intended as a competitor for the Thompson SMG in police and military contract sales. One of the last generation of "heavy metal" SMGs, the M42 used machined steel and polished wood much like the Thompson, though with a more streamlined design with easier takedown. Unable to commit to the design due to a massive orders for M2 machine guns, the design went to the United Defense Supply Corporation, a private outfit established and run by then-members of the British Purchasing Commission, who went to Marlin for the actual act of manufacturing. Originally sought out by the Dutch, a large quantity of M42s were left in the warehouse when the Netherlands fell to the Germans. The Office of Strategic Services and the U.S. Navy took interest in the surplus weapons, dropping them in occupied territories (which unfortunately included a large quantity captured in France by the Germans and handed over to the Milice), funneling them to the Nationalist and Socialist Chinese, as well as arming their own agents. In clandestine work, the M42 was noted as being vulnerable to sand and mud and in need of diligent maintenance, but it was easier to clean and had a higher potential accuracy out to 100 yards. Fitted with a fixed blade front and windage/elevation adjustable rear sights, with a circled "P" stamped on the right side of the chamber, the three-line address and model markings on the left side of the trigger housing, and the three-position selector ("SEMI-AUTO", "-SAFE-" and "AUTO") on the right side. Contoured front pistol grip and smooth buttstock with a checkered steel trapdoor buttplate. The left side of the trigger housing is marked "BPDW12" in electric pencil, with a decal on the right side of the stock identifying the item as the property of the City of Berkeley, Missouri; it was likely acquired post-WWII for use as a police weapon. Two extra magazines and a green nylon sling are included.

Very fine, with 85% plus of the original parkerized finish, showing areas of gray and brown patina, bright edge wear and minor handling marks. The furniture is very good, with a number of scattered dents and scratches. Mechanically excellent. NOTE: This weapon is a National Firearms Act (NFA), fully transferable Class 3, which is registered with the Bureau of Alcohol, Tobacco, Firearms and Explosives, (BATFE) that is classified as a "Curios or Relic" as defined in 27 CFR, 478.11. These weapons are still subject to the provisions of 18 U.S.C. Chapter 44 and 27 CFR part 479.