 Developed in the 1990s and 2000s the personal defense weapon, a compact submachine gun-like firearm which can fire armor-piercing, higher-powered ammunition began to replace the machine pistol as a self-defence side arm for artillery crews, tank crews, and helicopter pilots.Introduced in 2001, the Heckler & Koch MP7 is often called a machine pistol.The MP7 uses a short stroke piston gas system as used on H&K's G36 and HK416 assault rifles, in place of a blow-back system traditionally seen on machine pistols.