In a surprise move, the U.S. Army is asking industry for ideas for a new submachine gun. The last time the Army adopted a submachine gun was in 1943. It’s not clear why the Army wants a new subgun but it likely has to do with the service's eventual adoption of a new rifle caliber and new assault rifle.
Submachine guns were developed during the World War I as an alternative to bulky, slow-firing bolt action rifles. Short and firing pistol caliber ammunition, they were ideal weapons for assault troops clearing narrow trenches of enemy troops. The U.S. Army went into World War II with the M1928A1 Thompson submachine gun, which fired the same .45 ACP round as the M1911A1 pistol. Towards the end of the war the Thompson was supplemented by the , also in .45 ACP.
Submachine guns were eventually replaced in many armies by shortened assault rifles, which used heavier assault rifle rounds while still physically compact. In the U.S. Army, the M3 was used up through the 1991 the Gulf War by vehicle and by Delta Force.
According to , the U.S. Army has posted a Request for Information from the defense industry for a new submachine gun. is for a Sub Compact Weapon (SCW) that will fire 9x19-millimeter (9mm Luger) ammunition, have full automatic capability, a for attaching lights, optics, and other accessories, and mentions the capability to mount a suppressor.
Why is the Army going back to submachine guns? The service has made clear that it is looking to adopt a new round, possibly the 6.8-millimeter, round for its Next Generation Squad Automatic Weapon and next generation carbine. While the M4A1 carbine with its 5.56-millimeter round is small and light enough to equip vehicle crews and rear area troops, a 6.8 weapon could be heavier and bulkier, making it difficult to store in a truck cab. A 6.8 weapon would probably have more recoil, and rear area troops get less range time than their frontline counterparts.
A 9-millimeter submachine gun that was easy to carry, had less recoil, and could be used in self-defense would be desirable for troops infrequently exposed to combat. Nine millimeter also means the SCW would use the same ammunition as the new M17 Modular Handgun System.