Heckler Koch HK P11 underwater pistol (Germany)

The Heckler Koch P11 underwater pistol was originally developed during late 1960s by famous German arms-making company Heckler und Koch GmbH. Designed and produced under the cloud of secrecy, it was patented in 1969, but related patents were made public only in 2008. It was adopted by combat swimmers of the Bundeswehr (armed forces of the FRG) in 1976. Several other countries adopted this unusual weapon for its special forces, including US Navy. It remained secret until 1990s, when first photos of this gun began to appear in the press. It is an extremely interesting and unusual weapon. While its major rivals such as Russian SPP-1M pistol or American Mk.1 UDP are optimized to underwater (submerged) operations, the HK P11 pistol can be effectively used both underwater and above the water, “on air”.

Heckler Koch HK P11 underwater pistol, with fired underwater projectile shown below

This “dual medium” capability is achieved by using two types of ammunition. One type, the 7.62x36mm DM101, is intended for use in the water. It is loaded with a needle-like projectile about 10-11 cm long. Its weight and muzzle velocity differ from source to source, and are given either as 10 grams and 180 m/s or 32 grams and 117 m/s. In the latter case, it appears that the projectile is made from tungsten alloy. Projectiles are fired from smooth-bore barrels, assembled into the cluster of five inside a cylindrical “barrel block” made of plastic. Stabilization in water is achieved by hydrodynamic effects. Claimed effective range against a scuba air tank is 10 meters at the depth of same 10 meters. When fired “above the water”, those projectiles lack stability and thus have rather poor accuracy. Therefore, another type of ammunition, the 7.62x36mm DM91, is issued along with the HK P11 pistol for use “above the water” This ammunition is loaded with traditionally shaped pointed bullets with tungsten alloy core. Bullet weight is 8.6 gram and muzzle velocity is 190 m/s. Each bullet is loaded into the special plastic sabot, and is fired through a rifled barrel. Five barrels are assembled into the detachable barrel cluster, externally similar to that used for underwater shooting. Upon firing the DM91 cartridge, its sabot jams itself in the constriction at the muzzle of the barrel, capturing hot powder gases inside the barrel. This feature ensures silent and flash-less discharge, similar in effect to Soviet noiseless pistols such as MSP or S4M.

7.62x36mm DM91 cartridge for the HK P11 pistol, for the “above water” use

HK P11 pistol patent diagram

Both types of barrel clusters are interchangeable, and attached to the plastic gun frame for firing. Barrels can be loaded and re-loaded only at the factory; for field use, each Heckler Koch P11 underwater pistol is issued with several pre-loaded barrel clusters. Under normal “practice” use fired clusters are collected and sent back to the factory for reloading. Muzzle of each barrel in the cluster is protected by a water-tight diaphragm which is destroyed upon firing.
Pistol frame is made of same black plastic and has a grip with the trigger unit, manual safety and barrel cluster lock. Pistol features electric trigger system, powered by two 12-volt batteries stored in a water-tight container inside a pistol grip. As such, each cartridge features special primer which is ignited by electric current. Each barrel cluster is fitted with fixed “iron” sight with luminous tritium inserts.

Heckler Koch HK P11 underwater pistol, with barrel cluster detached

Heckler Koch HK P11 underwater pistol, front view showing pierced diaphragms that protect each loaded barrel from the water