Heckler & Koch MP5N

MP5N from Half-Life, as seen by the player

The MP5 is an air-cooled, roller-delayed blowback operated submachine gun chambered for the ubiquitous 9 x 19mm Parabellum round. Developed by Heckler and Koch GmbH of Germany, it is typically fed from 30 round magazines, weighs 6.35 pounds for the A3/Navy model, and has a rate of fire of approximately 700-800 rounds per minute, depending on the type of ammunition used. It is known for its excellent accuracy stemming from the closed-bolt operation it utilizes, and its reliability, modularity, and user-friendliness. It is one of the most widely-adopted submachine guns in the world, remaining very popular with counter-terrorist organizations and militaries despite its age.

The MP5 was first introduced by Heckler & Koch in 1966, under the name HK54. This name comes from HK's old numbering system: the "5" designates the model as a submachine gun, while the "4" identifies it as being chambered for 9 × 19 mm ammunition. The current name dates from when it was officially adopted by the West German government for use by its police and border guard as the Maschinenpistole 5 ("Machine pistol 5", or MP5), in mid-1966. The GSG 9 (the counter-terrorist unit of the German Federal Police) then introduced the MP5 to other Western counter-terrorist units.

Under a special contract from the United States Navy, Heckler & Koch developed the MP5N ("N" standing for "Navy") variant for the Navy's elite special operations units (including the U.S. Navy SEALs). The MP5N is a standard MP5 with a fully ambidextrous Navy trigger group (with safe, semi- and fully automatic modes), a retractable stock, and a threaded barrel for mounting stainless steel suppressors. This variant of the weapon was employed by the HECU, along with an underslung 40mm grenade launcher. The weapon was also used in conjuction with custom built 50 round magazines. This combination gave even greater capabilities to the already excellent design.