A submachine gun is a type of gun that shoots many bullets, usually pistol bullets, when one holds down the trigger. A submachine gun is smaller than a machine gun and can easily be carried by one person. They are often used where people need to defend themselves in small areas, or people need to fire many bullets quickly. The first submachine guns were invented in the early 1900s. They are often used by the police.
In the early 20th century, experiments were made by converting pistols from semi to fully automatic firearms. Stocked (with handle) automatic weapons firing pistol rounds were developed around the same time during World War I, by Italy, Germany, and the United States. The first dedicated designs were developed in the latter stages of World War I both as improvements on earlier stocked pistols, and to offer an advantage in trench warfare.
They were popularized in the 1920s and '30s as weapon of choice of American gangsters and police, in the form of the famous Thompson submachine gun, commonly referred to as the "Tommy Gun". Submachine guns rose to prominence as a frontline close-quarters combat weapon and commando firearm during World War II. They are now widely used by police SWAT, military commando, paramilitary, and counter-terror team members for a variety of situations. Submachine guns are highly effective in close quarters; their lower-powered pistol cartridges make them generally more controllable in fully-automatic fire compared to assault rifles, while their small size and light weight grant maneuverability. However, pistol cartridges generally have low effectiveness against targets protected by body armor or cover, and are short-ranged compared to intermediate and rifle cartridges.