Some different types of machine guns include automatic and semi-automatic guns and standard and submachine guns. Fully automatic machine guns automatically reload cartridges and continue to fire as long as the trigger is held. Semi-automatic machine guns automatically reload cartridges but require the trigger to be pulled to fire.
Standard machine guns use rifle ammunition. Submachine guns fire cartridges designed for pistols. The Thompson "Tommy" gun developed by John W. Thompson in 1918 is an example of a submachine gun. This gun became famous during the Prohibition era and was used by criminals and law enforcement personnel alike. It used a large .45 APC cartridge.