The Heckler und Koch submachine gun, MP-5, is one of the most famous and wide-spread firearms of its class, developed since the Second World War. Its development began circa 1964 under the company designation HK MP-54, or simply HK 54. In the 1966, German police and Border Guard adopted the HK 54 as the MP-5, and it was originally available in two forms - MP-5 with fixed buttstock and MP-5A1 with retractable buttstock. Some years later HK slightly upgraded the design of MP-5, replacing the sights (from flip-up open notch rear and blade front to drum-type diopter rear and hooded post front) and the muzzle (replacing the two-slot muzzle compensator to the tree-lugs QD silencer mount without compensator). Other improvements made over the time concerned the magazines (early type magazines were of straight box type, latter - of curved box type for improved reliability). The trigger units also were upgraded - from original stamped steel with plastic grip to the all-plastic units, integral with grip, and with various fire modes and marking. Over the years MP-5 were adopted by the huge numbers of police, security and military forces around the world, including the German police and border guard, British police and elite Army SAS units, American police, FBI, Navy and Marine Corps, and many, many others. MP-5 is still manufactured in Germany by the HK itself, and also licensed to Greece, Iran, Pakistan and Mexico. The only real rival to the MP-5 in the terms of proliferation across the world is the famous Israeli UZI submachine gun. Most interestingly, the German Army (Bundeswehr) did not adopted the MP-5, most probably due to the economical reasons, and turned instead to the... UZI submachine guns, made under license in Belgium.
The success of the MP-5 is outstanding. It is based on the high quality and reliability of the gun, great single-shot accuracy (thanks to its closed bolt action), great flexibility and, of cause, good marketing. It seems that no other modern SMG at this time can rival the MP-5 in popularity (UZI is not manufactured anymore).
The MP-5, basically, is no more than the scaled-down version of the Heckler-Koch G3 battle rifle. It shares the same basic design with stamped steel receiver and the same roller-delayed blowback action, derived from the post-war CETME rifles. The trigger units are hinged to the receiver and are now available with various fire mode options, including 2 (Safe, Semi-auto), 3 (Safe, Semi, Full Auto) or 4 (Safe, Semi, Limited burst of 2 or 3 rounds, Full auto) position levers, ambidextrous or not, and marked with letters, digits or icons. The MP-5 is always fired from closed bolt for improved accuracy, but this limits the amount of sustained fire due to the barrel overheating and resulting cook-off problems. To avoid this, MP-5 cocking handle could be locked in the rear position in the special slot, leaving the bolt in the open position, with no cartridge in the chamber. To commence the fire one must simply release the cocking handle from its notch and then pull the trigger. Modern MP-5 submachine guns are equipped with three-lug quick detachable silencer mounts on the barrel. Sights are similar to other HK models, and consists of the front hooded post sight and the adjustable for windage and elevation drum-type diopter rear sight. Special quick-detachable clamp mounts allows for installation of night, optical and red-dot sights if required. Standard magazine capacity is 30 rounds, but shorter 15 rounds magazines are available. Special versions were developed and manufactured in limited numbers during 1980s-90s for the US Law Enforcement market, chambered for more powerful 10mm Auto (10x25mm) and .40S&W (10x22mm) ammunition. These guns can be easily distinguished from more common 9mm models by straight box 30 rounds magazines, made from plastic.
While all of MP-5 can be fitted with silencers, there also a dedicated silenced version of MP-5, called MP5SD2 or SD3 (depending on the stock type). This version is equipped with non detachable integral silencer, and the vented barrel, to reduce the bullet muzzle velocity down below the speed of sound. The MP-5SD is intended to fire standard 9mm ammunition, not the special subsonic one.
Semi-automatic only versions of the MP-5 were once made for civilian market under the designation of HK-94, some with longer, 16 inch (406 mm) barrels, to conform with US laws. There also is an US company, called Special Weapons LLC, that is manufacturing semi-automatic, civilian MP-5 clones in various pistol calibers, including the .45ACP. This article uses material from the Modern Firearms & Ammunition site article "Heckler und Koch MP-5 (Germany)".