THE UNITED DEFENSE M42 SUBMACHINE GUN.
Also developed as a possible replacement for the Thompson was the M42 submachine gun. Carl G. Swebilius of the High Standard Manufacturing Company designed the M42 in 1940, with a patent filed on October 15, 1940, and assigned to High Standard. However, High Standard was producing .50 Browning Machine Guns for the British, which left little production capacity for a new SMG. The United Defense Supply Company, a US. Government entity tasked with weapons development and acquisition for the U.S. armed forces carried out further development. Though this SMG would be generally known as the UD (United Defense) M42, actual production was by the Marlin Firearms Company. According to some sources, after United Defense received a contract to supply M42s to the Dutch, High Standard purposely was slow in providing blue prints to Marlin for the M42, causing early difficulties in tooling up for production. High Standard's tolerances were also not designed to allow parts to fully interchange; hence, Marlin had to re-engineer the design for large-scale military production.
Initially, there was great optimism about the future of the M42, with 1942 negotiations calling for up to 150,000 of the SMG to be produced by Marlin, with full production reaching 1,000 units a day. Marlin would produce the M42 for $46 each. The SMGs would be marked "United Defense Supply Corporation" and inspection and delivery of the weapons to the armed forces would be through United Defense, which would collect $53.00 for each SMG, equivalent to $810 in 2018 dollars. The M42 was fabricated of machined steel, thus keeping the cost high. NOTE: A small number of M42s were produced and marked "High Standard."
Adoption of the M3 SMG, however, eliminated the need for the M42, especially since production cost for an M3 was $18.36. The 9x19mm chambering of the M42 was also a disadvantage, as .45 ACP ammo for the M1911A1 pistol, Thompson SMG, and M3 SMG was already in the supply system, while 9x19mm ammunition was not. There were a few M42 prototypes produced by High Standard in .45 ACP and tested at Aberdeen Proving Grounds in 1940, but production guns were in 9x19mm caliber. One U.S. customer -the Office of Strategic Services (OSS)--deemed the 9x19mm chambering advantageous.
Since OSS agents would be operating behind enemy lines in Europe and raising and training resistance fighters, the availability of an SMG that would fire the standard German 9mm Parabellum (9x19mm) cartridge was deemed a positive feature. As a result, a smaller order was placed with Marlin for 15,000 M42 SMGs. See below for an alternate explanation of OSS acquisition of the M42. Some sources state that as many as 6,000 UD M42s were dropped into France during 1944, while a more likely figure is around 2,400. OSS and SOE (Special Operations Executive) used the M42. One of the best-known examples of the M42's employment was by British SOE agents during the kidnapping of German General Kreipe on Crete in April 1944.
Other M42s reportedly saw service with OSS or SOE teams in the Far East, though the Ml Carbine was generally more popular with OSS Detachment 101 and other Far East units. However, there do seem to have been instances of the M42 being supplied to Chinese or Philippine guerrillas. Some UD M42s likely saw service with naval units of some type, as examples have been encountered in wooden boxes with dividers for magazines of the type often used on naval vessels. These may have been issued to the OSS Maritime Unit, which infiltrated agents into AOs (Areas of Operation) by sea.
There was a reported commercial order by the Dutch for M42s, which were supposedly shipped to the Dutch East Indies just prior to the Japanese invasion in December 1941. However, the dates are hard to reconcile with the production dates of the M42. Perhaps, a couple of High Standard prototypes were sent before the invasion, but it is doubtful if any production guns reached the Dutch East Indies, unless they were supplied to guerillas by the OSS or SOE. Another source states that the M42s were delivered to the Dutch Purchasing Commission, but by that time, the Dutch East Indies had fallen to the Japanese. As a result, the weapons were sold to the U.S. Government, with a substantial number of them going to the OSS.
Although expensive to produce, the M42 was a simple straight-blowback, select-fire, open bolt design. One of the noteworthy features was the cocking handle, which was not really a handle, but a longitudinal slide on the right of the receiver. It was not captive to the bolt, so after cocking the bolt, the slide could be pushed forward. There is a hold-open device consisting of a lug forced up to block the bolt by the magazine follower after the last round is fired. The standard stick magazine held 25 rounds, but some magazines were welded together back-to-back and upside down, much as many U.S. troops used to tape a pair of M16 magazines. NOTE: It is very common to see sources that state the M42 magazine holds 20 rounds. This is probably because there are only four witness holes in the magazine, implying only 20 rounds. However, 25 rounds is the correct capacity.
The combination of the bolt hold open, the well-designed magazine release lever, and the paired magazines made for a quick reload; however, the double magazine proved problematic, as the exposed lips of the magazine facing down were easily damaged. The magazines also had a tendency to warp, causing malfunctions. The UD M42 was nicely machined to close tolerances, which proved a disadvantage when exposed to mud or sand.
I mentioned the magazine-release lever above. If the magazine is grasped as the thumb depresses the lever, it may be stripped quickly. The selector switch is also convenient for operation by the trigger finger. Settings are "SEMI-AUTO," "SAFE," and "AUTO." Elevation and windage are readily adjustable using dials. The elevation adjustment dial was obviously de- J signed by an optimist, as it can raise the aperture sight to a distance beyond likely use for an open bolt SMG.
Disassembly is relatively easy, as turning a lever on the right side of the receiver allows the receiver to be pulled forward and up away from the frame. The operating spring and bolt may then be removed from the receiver to the rear. We had done quite a bit of shooting prior to disassembling the M42 and found that fouling made disassembly substantially more difficult. During the early Aberdeen trials of the M42, its ease of disassembly was cited as one of its advantages.
I've shot the UD M42 a couple of times in the past, but decided to use this article as a chance to shoot it again. I put 250 rounds through the example I had available. I fired mostly in short bursts, but also fired semi-auto at 50 yards to test accuracy when aiming carefully. Reliability was very good, with the only malfunctions I remember occurring with failures to fully feed the last round in the magazine a couple of times. Ergonomics of the M42 are better than many other SMGs, especially the ease of magazine changes and the convenient location of the selector. The cocking slide does not protrude much and would, I think, offer some difficulty in cold weather when wearing gloves or in driving it back to extract a stuck case. The vertical fore grip was a real aid in con-trolling the M42 on bursts. Although I have not read of cases of the fore grip breaking during combat use, its design appears to offer that possibility, should it be struck hard on a vehicle body or other surface or dropped on rocks (never a good idea with an open bolt SMG in any case).
It is worth noting with the M42 that pulling the bolt back to the locked-open position automatically moves the selector to the semi-auto position. As a result, the operator must consciously move it back to safe if that setting is desired.
As was previously mentioned, the M42 handles well on full auto. Firing in five- to six-round bursts at 10 yards and three- to four-round bursts at 15 yards, all bullets scored hits on a man-sized silhouette. Although the M42 was not intended to replace a rifle at longer ranges, 50-yard, five-shot semi-auto groups ran in the 3.5- to 4-inch range; not bad for an open bolt SMG.
Submachine gun aficionados generally rate the UD M42 one of the better World War II-era SMGs. I agree with that evaluation. Unfortunately, it was developed at a time when speed of production and cost factors made the M3 SMG more appealing for general issue. All reports that I've seen indicate that the .45 ACP prototype M42s performed well, so caliber would not have been an issue. As it transpired, its 9x19mm chambering made it appealing to the OSS, the user that has given the M42 its cachet. As it was used by the OSS, I have always wondered if a suppressed version was contemplated.
In the USA, the UD M42 is a relatively scarce SMG, but I have been told that many arms museums in France have examples. That would seem to substantiate the reports that many were dropped. I have visited the Norwegian and Dutch Resistance Museums multiple times but do not remember seeing an M42. They mostly had Stens.
I've been negotiating with one of my book publishers to do a book on World War II clandestine weapons. Shooting the UD M42 again reminded me that it definitely belongs in the chapter on submachine guns.
Caption: The UD M42 is one of the most controllable world War II-era SMGs when firing bursts.
Caption: Left-side view of the UD M42; the "dial" on the left rear of the receiver is to adjust the rear sight's elevation.
Caption: Right side view of the UD M42; its machined steel parts and wood furnishings mark it as an "old school" SMG that proved too expensive for U.S. adoption.
Caption: The much less labor-intensive and less-expensive M3 "Grease Gun" was adopted by the U.S. armed forces over the M42.
Caption: This M42 shows wartime wear on the stock and vertical fore grip, but still functions reliably.
Caption: The M42's cocking slide does not protrude, thus lessening the chances of catching on something, but also offering little surface to grip if necessary to force the bolt back.
Caption: Most writers who have not fired an M42 state that the magazine holds 20 rounds, but this is incorrect. Correct magazine capacity is 25 rounds.
Caption: The M42's magazine is well designed for quick changes if the magazine is gripped with the support hand while depressing the magazine-release lever with the thumb.
Caption: The M42's selector is well located for operation by the trigger finger.
Caption: Close-up of the dial to adjust elevation on the rear aperture sight.
Caption: The M42's ramped blade front sight.
Caption: The UD M42 takes down into its primary parts quickly and easily.
Caption: Note how controllable the M42 is when firing bursts.
Caption: The vertical fore grip is a real aid in controlling the M42 on full auto, but it does appear somewhat fragile in hard use.
Caption: The rear aperture sight allows accurate firing at 50-100 yards.
Caption: M42 controls, including the selector switch, cocking slide, magazine release, and takedown lever.
Caption: Another view of burst firing.
Caption: Group fired at 10 yards using five-to six-shot bursts.
Caption: The M42's butt plate incorporates a compartment for cleaning tools.
Caption: View of the M42's ejection port.
Caption: Five-shot, semi-auto, 41/2-inch group fired at 50 yards.
UNITED DEFENSE M42 SMG ACCURACY TEST 50 yards, five shots Black Hills 147-grain FMJ 3 3/4" Sellier & Bellot 115-grain FMJ 4 1/4" SIG-Sauer 115-grain FMJ 3 3/8" UD M42 SPECIFICATIONS Action: Select Fire, Open Bolt, Blowback Caliber: 9x19mm Overall Length: 32.3" Barrel length: 11" Weight: 10 lbs. (loaded) Magazine Capacity: 25 rounds (two conjoined magazines an available option) Sights: Rear-Aperture adjustable for elevation and windage, Front-Blade Cyclic Rate on 700 RPM Full Auto: