During the late 1960s Soviet engineers worked on providing a new kind of weapon for specialist troops operating underwater. This became the Simonov SPP-1 "underwater pistol" introduced in 1971. Design of the SPP-1 fell to Vladimir Simonov who also lent his talents to the upcoming APS "underwater assault rifle" of 1975 (detailed elsewhere on this site). The cartridge was a joint design approach headed by Oleg Kravchenko and Pyotr Sazonov. Manufacture of the pistol has been through TOZ / Tula Arms Plant and the pistol may still be in service with Russian special forces today (2015).
The SPP-1 fires a specially-made 4.5x40mmR 5.7"-long cartridge (essentially a small, slim dart fitted as the nose of a standard Soviet 7.62x39mm case) from a unique four-barreled arrangement (stacked as 2x2 square). Reloading involves a break-action system which exposes the barrels near the breech of the gun. Four darts are clipped as a single unit for ease in reloading. The trigger is of a Double-Action (DA) design and a smoothbore barrel guides the projectile at least to the muzzle of the firearm. From there, hydrodynamics are relied upon to keep the outgoing projectile on its path towards the target - effective range underwater being about 55 feet in 16 feet of water. As pressures change in deeper water, range and effectiveness is reduced. This design element limits the value of the SPP-1 when firing out of the water as the smoothbore barrel does not aid in ranged accuracy as much - effective range being about 50-60 feet with accuracy variable. Muzzle velocity is rated at 790 to 820 feet per second. Nevertheless, this is a weapon for specialist troops to be fired under special conditions and in that role it succeeds.
The weapon is not necessarily compact featuring a length of 9.6 inches, a width of 1.5 inches and a height of 5.4 inches. Weight is about 36 ounces when loaded. The large trigger ring makes the weapon particularly cumbersome.
The "SPP-1M" model was brought along with some refinements to the base SPP-1 design, namely in introducing an additional spring for improved trigger pull and an enlarged trigger ring so the weapon could be more easily used by a gloved hand.
Despite its 1960s origins, the SPP-1 was not publically revealed until the 1990s.