The SPP-1 Underwater Pistol was a specialist pistol built for the Soviet frogmen for use in covert missions underwater. The SPP-1 was designed to fire a hydrodynamic dart fired from one of the four barrels, each chambered to accept the 4.5x39mmR cartridge.
Design Details
The SPP-1 was manufactured with four barrels, each firing one dart. The darts are loaded via a clip pushed into the breech, as the barrel is hinged underneath to allow the breech to be accessed. This means that the SPP-1 can be easily reloaded both above or below the surface of the water. These barrels are not rifled, as the dart uses hydrodynamic effects to remain travelling in a straight line rather than aerodynamics as a conventional bullet would use. The SPP-1 is manufactured with a double action firing mechanism, meaning that each time the trigger is pulled a single dart is fired. Only when all four cartridges/darts are fired can the SPP-1 be reloaded. The double action system consists of a rotational striker which is rotated to the next barrel after the dart is fired, much like how a revolver's cylinder is turned by the trigger pull. The SPP-1 is effective to a depth of 40m (130ft) at which point the dart will struggle to overcome the pressure of the water around it. At lower depths it is possible that the SPP-1 will fail to operate entirely.
Safety is dealt with via a lever with three positions. This lever has three positions the first to allow the SPP-1 to be loaded (up position), the second position indicated the SPP-1 was safe (middle position) and the final position indicated that the SPP-1 was ready to fire (down position).
Ammunition
The SPP-1 fires a 115mm (4.5in) long steel dart, measuring 4.5mm (0.18in) in diameter. This dart is attached to a water-tight 4.5x39mmR cartridge used by other Soviet weaponry. The dart and cartridge weigh 12.8g (195gr) together.
The SPP-1's dart is designed to use hydrodynamic effects to remain stable, rather than a conventional bullet which uses aerodynamic effects to remain stable. This means that the SPP-1, while being relatively accurate underwater, above water is inaccurate but is capable of penetrating 5mm of glass/face plate or a padded underwater suit at a distance of around 15m both above or below the surface of the water.
SPP-1M
The SPP-1M is an improved version of the SPP-1, focusing on improving the usability of the SPP-1 in the water. Various functional modifications were made, however the major changes were made to the ergonomics of the design which meant that the SPP-1M's trigger could be pulled better due to thetrigger guard being extended to accomodate diving gloves. Furthermore a spring was added above the sear, intended to shorten the trigger pull and therefore mean that the SPP-1M would be quicker to fire underwater.
Usage
The SPP-1 Underwater Pistol was designed to be used by Soviet Frogmen, as the Cold War demanded more covert missions against either side. The SPP-1, and later SPP-1M, were intended to allow the Soviet Frogmen to attack enemies underwater more effectively than an ordinary pistol/revolver.
The SPP-1 would become a longer lasting alternative to the Heckler & Koch P11, an electronically fired underwater pistol. The SPP-1, thanks to its entirely mechanical mechanism, was simpler and more practical to use than the P11, particularly due to the fact that the P11 would have to be sent back to Heckler & Koch to be reloaded. Yet some forces did choose the P11 over the SPP-1 as the P11 has six-barrels, meaning six shots.
References
http://en.wikipedia.org/wiki/SPP-1_underwater_pistol
http://world.guns.ru/handguns/hg/rus/spp-1m-underwater-e.html