[15] The MP5 is one of the most widely used submachine guns in the world, having been adopted by over forty nations and numerous militaries, police forces, intelligence agencies, security organizations, paramilitaries, and non-state actors.

[19] Heckler & Koch, encouraged by the success of the G3 battle rifle in 1959, developed a family of small arms consisting of four types of firearms all based on a common G3 design layout and operating principle.

The MP5 was created for the fourth type as the HK54; under the HK naming system, this categorizes it as a selective fire carbine chambered in a handgun cartridge.

[21] The MP5 has since become a mainstay in militaries, special forces, and police tactical units across the world, but has gradually been replaced since the late 1990s by rifles, carbines, and personal defense weapons due to changes in armament trends, including growing access to body armor that can stop handgun cartridges.

[24] The fixed, free-floating, cold hammer-forged barrel has six right-hand grooves with a 1 in 250 mm (1:10 in) rifling twist rate and is pressed and pinned into the receiver.

[25] The adjustable iron sights (closed type) consist of a rotating rear diopter drum and a front post installed in a hooded ring.

The rear sight drum provides four apertures of varying diameters used to adjust the diopter system, according to the user's preference and tactical situation.

This results in a calculated delay, allowing the projectile to exit the barrel and gas pressure to drop to a safe level before the case is extracted from the chamber.

A spring extractor is installed inside the bolt head and holds the case securely until it strikes the ejector arm and is thrown out of the ejection port to the right of the receiver.

The MP5SD's integral suppressor itself is divided into two stages: the initial segment surrounding the ported barrel serves as an expansion chamber for the propellant gases, reducing gas pressure to slow down the acceleration of the projectile.

The bullet leaves the muzzle at subsonic velocity, so it does not generate a sonic shock wave in flight.

As a result of reducing the barrel's length and venting propellant gases into the suppressor, the bullet's muzzle velocity was lowered anywhere from 16% to 26% (depending on the ammunition used) while maintaining the weapon's automation and reliability.

[34] The integral suppressor, built around its 5.7-inch barrel, uses a unique two-stage design that allows it to operate silently in most environments, including when wet, while still remaining reliable.

[35] The distinctive size of the integral suppressor gives it a unique handguard design, with a modified charging handle to account for it.

Developed from the stockless MP5A1,[30] it features a 4.5-inch barrel incompatible with muzzle attachments, an endcap with sling mount instead of a stock, and a unique handguard with a built-in foregrip.

Most components of the MP5K are shortened on account of its compact design, including its bolt, receiver, charging handle, cover, and trigger group frame; the lighter bolt gives it a higher rate of fire, at approximately 900 rounds per minute (as opposed to 800 rounds per minute with the regular MP5).

In the United States, PTR Industries,[65] Zenith Firearms,[66] Dakota Tactical,[67][68] and Century International Arms[69] manufacture semi-automatic clones of the MP5 that are legally classified as pistols.