1940, although the United States did not formally participate in World War II, it accelerated the pace of research and development of weapons and equipment. At that time, the US military was mainly equipped with Thomson submachine guns, which were heavy and expensive, so it planned to develop new models to replace them, and one of the achievements was the joint defense M42.
UD M42 was designed by Karl G. Sveiby of Gaobiao Company before World War II. There was probably no market demand at the beginning, so the attention was not high. After the outbreak of World War II, American weapons companies ushered in spring. Gaobiao Company registered a submachine gun patent at 1940, originally named UD M4 1. Because it was mass-produced in 1942, it was renamed UD M42.
At that time, because it focused on the production of M2 heavy machine guns, it signed a production contract with United Defense Supply Company.
UD M42 submachine gun initially fired 0.45 caliber ammunition, the same caliber as Thomson submachine gun. Only a few sample guns were produced, and they were changed to 9 mm caliber during production. The gun adopts a free bolt machine, and there are full automatic and semi-automatic shooting modes to choose from. The theoretical firing rate is about 700 rounds per minute, and the muzzle velocity is about 335 meters per second. It uses rifle butt, and there is another handle under the front guard.
The special feature of this gun is that it uses a straight magazine with a capacity of 25 rounds (the prototype gun with a caliber of .45 uses a magazine with a capacity of 20 rounds), but generally the two magazines are welded together, which is the same as some soldiers wrapping two magazines with tape, and the replacement is convenient and quick.
UD M42 submachine gun weighs 4.54kg and has a total length of 820mm. Compared with Thomson submachine gun, it has no obvious advantage in size, but it is also the same in performance. The gun uses machined parts, so it has no advantage over Thomson submachine gun in cost.
So what is the shooting performance of guns? In the design of the gun, the dustproof of the magazine is considered, but this is not a problem. It requires the shooter to avoid long-term continuous shooting as much as possible, reduce the wear of parts, and thus reduce the failure rate. In use, the magazine should be as far away from dust as possible, and the magazine itself is easy to deform, which affects the ammunition supply. Strictly speaking, the failure rate is acceptable as long as the gun is clean at ordinary times and the influence of dust is paid attention to in use.
This kind of gun also has its advantages, such as high accuracy in the distance of 100 meters, easy disassembly and cleaning, and has been well received in use.
UD M42 submachine gun failed to complete the expected idea of replacing Thomson submachine gun, and its cost determined that it could not be mass-produced. During the whole World War II, the gun produced about 15000 guns, most of which were supplied to European resistance organizations and guerrillas by airdrop, such as Italian, Belgian, Norwegian and other countries, and China and the Philippines also got some in that year.
Facts have proved that UD M42 submachine gun has performed well in actual combat, and it is the right choice to change it to 9 mm caliber, so guerrillas can use captured ammunition. The longest used one should be the Philippines, whose military and police forces were still in use in the 1960s. As for the task of replacing Thomson submachine gun, it was handed over to M3 "grease gun".