High Quality Content by WIKIPEDIA articles! A personal defense weapon (PDW) is a compact semi-automatic or fully automatic firearm similar in most respects to a submachine gun, but firing an (often proprietary) armor-piercing rifle round, giving a PDW better range, accuracy and armor-penetrating capability than submachine guns, which fire pistol-caliber cartridges. The class of weapon as it exists today evolved as a hybrid between a submachine gun and a carbine, retaining the compact size and ammunition capacity of the former while adding the ammunition power, accuracy and penetration of the latter.