Why did World War II armies produce large numbers of simple submachine guns?

During World War II, armies produced large numbers of simple submachine guns primarily to meet the urgent need for increased firepower at close quarters. As combat evolved, the greater mobility of troops accompanying armored vehicles necessitated lighter, more portable weapons that were easier to handle than traditional rifles during offensive assaults.12

To meet these demands, major powers developed a second generation of submachine guns designed for mass production. By utilizing sheet-metal stampings, these weapons could be manufactured inexpensively and in large quantities almost anywhere. This shift toward simplified, cost-effective designs—such as the British Sten gun, the German MP40, and the American M3—allowed military forces to rapidly arm vast numbers of soldiers with automatic weapons capable of providing rapid fire in confined environments. These weapons effectively filled a tactical gap, offering superior handling and rate of fire compared to handguns, even if their effective range was limited to approximately 200 yards.21