special forces units for close-quarters combat, due to their reduced size, recoil and muzzle blast. Submachine guns also lend themselves to the use of suppressors, particularly when loaded with subsonic ammunition. Variants of the Sterling and Heckler & Koch MP5 have been manufactured with integral suppressors. Only a limited number of new submachine gun designs had been adopted during this period, such as the Brügger & Thomet APC and SIG MPX. Personal defense weapons First developed during the 1980s, the personal defense weapon (PDW) is touted as a further evolution of the submachine gun. The PDW was created in response to a NATO request for a replacement for 9×19mm Parabellum submachine guns. The PDW is a compact automatic weapon that uses specially designed rifle-like cartridges to fire armor-piercing bullets and are sufficiently light to be used conveniently by non-combatant and support troops, and as an effective close quarters battle weapon for special forces and counter-terrorist groups. Introduced in 1991, the FN P90 features a bullpup design with a futuristic appearance. It has a 50-round magazine housed horizontally above the barrel, an integrated reflex sight and fully ambidextrous controls. A simple blowback automatic weapon, it was designed to fire the proprietary FN 5.7×28mm cartridge which can penetrate soft body armor. The P90 was designed to have a length no greater than an average-sized man's shoulder width, to allow it to be easily carried and maneuvered in tight spaces, such as the inside of an infantry fighting vehicle. The P90 is currently in service with military and police forces in over 40 nations. Introduced in 2001, the Heckler & Koch MP7 is a direct rival to the FN P90. It is a more conventional-looking design, and uses a short-stroke piston gas system as used on H&K's G36 and HK416 assault rifles, in place of a blowback system traditionally seen on submachine guns. The MP7 uses 20-, 30- and 40-round box magazines and fires the proprietary 4.6×30mm ammunition which can penetrate soft body armor. Due to the heavy use of polymers in its construction, the MP7 is much lighter than older SMG designs, being only with an empty 20-round magazine. The MP7 is currently in service with military and police forces in over 20 nations. See also Assault rifle Firearm action List of submachine guns Machine gun Machine pistol Overview of gun laws by nation Personal defense weapon Semi-automatic pistol Sputter Gun References