The Heckler & Koch MP5 (from German: Maschinenpistole 5, "machine pistol model 5") is a 9mm submachine gun of German design, developed in the 1960s by a team of engineers from the German small arms manufacturer Heckler & Koch GmbH (H&K) of Oberndorf am Neckar.
The MP5 is currently one of the most widely used submachine guns in the world, having been adopted by 40 nations and numerous military, law enforcement, intelligence, and security organizations. In the 1990s, Heckler & Koch developed the Heckler & Koch UMP, the MP5's successor, though both remain in production.
Heckler & Koch, encouraged by the success of the G3 automatic rifle, developed a family of small arms consisting of four types of firearms (all based on a common G3 design layout and operating principle), where the first type was chambered in 7.62×51mm NATO, the second—using the 7.62×39mm M43 round, third—the intermediate 5.56×45mm NATO caliber and the fourth type—chambering the 9×19mm Parabellum pistol cartridge. The MP5 was created within the fourth group of firearms and was initially known as the HK54.
Work on the MP5 began in 1964 and scarcely two years later it was adopted by the German Federal Police, border guard and army special forces.
The MP5 is manufactured under license in several nations including Greece (formerly at EBO - Hellenic Arms Industry, currently at EAS - Hellenic Defense Systems), Iran (Defense Industries Organization), Mexico (SEDENA), Pakistan (Pakistan Ordnance Factories), Saudi Arabia, Sudan (Military Industry Corporation), Turkey (MKEK), and the United Kingdom (initially at Royal Ordnance, later diverted to Heckler & Koch Great Britain).
The primary version of the MP5 family is the MP5A2, which is a lightweight, air-cooled, selective fire delayed blowback operated 9×19mm Parabellum weapon with a roller-delayed bolt. It fires from a closed bolt (bolt forward) position.
The fixed, free floating, cold hammer-forged barrel has 6 right-hand grooves with a 1 in 250 mm (1:10 in) rifling twist rate and is pressed and pinned into the receiver.