The first true submachine guns saw combat in World War I, where they proved an asset in trench warfare. During the Prohibition era in the United States, the Thompson submachine gun grew infamous for its heavy use by gangsters and police officers, and was later used by U.S. soldiers in WWII. Submachine guns were used by all sides in WWII to provide soldiers (who were typically armed with bolt-action rifles) with superior close range firepower, and continued to see service afterwards, but were soon usurped as standard military weapons by automatic rifles. In recent years, submachine guns have mainly been used by law enforcement officers, counter-terrorism operatives and special forces soldiers, but they have begun to fall out of favor with these groups due to their poor effectiveness against modern body armor.
Sub-machine guns occupy the middle ground between pistols and rifles in terms of effectiveness. They're lighter and shorter than rifle carbines, making them easy to maneuver in close quarters, and have somewhat softer recoil. On the other hand, they're less accurate at range than most rifles and have inferior stopping power. Despite this, submachine guns (and their semi-automatic equivalents) are far
more practical than machine pistols (due to their more ergonomic layout) and they will suffice for a primary weapon if you should come across one, though a rifle is preferable. If you do choose to use a submachine gun, it is important to keep it on semi-auto mode, as fully automatic fire is only a waste of ammo against zombies. The temptation to go full auto may be an argument against the use of these weapons by some people. Well known submachine gun designs include the Thompson submachine gun, the IMI Uzi, the MP-40 and the H&K MP5.
Personal defense weapons (PDWs) are a relatively recent development in firearms designs.
Designed to fire newly small-caliber cartridges which are similar to scaled-down rifle cartridges, personal defense weapons can display superior penetration and velocity when compared to the pistol munitions used in submachine guns. The two most well known designs in this category are the FN P90 and the H&K MP7.