Special forces elements have long since required specialized weapons and training to see their particular mission set through. As such there were many types of unique weapon designs that permeated the Cold War decades during which many of today's special forces groups were established. One of the more interesting categories of firearm became the "underwater pistol", a weapon that - as its name suggests - gave the special forces member the capability to fire under water. Such weapons were developed in the United States and the Soviet Union as well as Germany.
In the 1970s, the West German concern of Heckler & Koch began development and testing of an underwater pistol and, in 1976, the weapon was introduced as the "P11" (though it was not formally recognized publically until 1997). It utilized a five-barrel module arrangement with each barrel chambered to fire a 4-inch long steel dart. Power was electrical and served from a battery pack embedded in the pistol grip handle. These components coupled together - along with the trigger group - made for a large handheld weapon but one that was nonetheless deemed effective for its intended role.
The P11 use of steel darts was common practice for underwater weapons as standard, land-based cartridges were found to perform poorly when fired in water. The darts were officially of 7.62x36mm Special caliber and held an underwater range up to 50 feet. If pressed, the weapon could also fire above water (though with reduced accuracy) up to a range of 100 feet. Sights were fitted to the weapon to provide for some accuracy at range. Once expended the weapon's entire five-barrel module was simply replaced. The module barrels themselves were only reloadable at the HK factory.
Beyond its use by German special forces (GSG-9), the P11 went on to see adoption by various other nations including Denmark, France, Israel, Italy (COMSUBIN), Malaysia (PASKAL), Netherlands, Norway, the United Kingdom (Special Boat Service), and the United States (Navy SEALs).