The Internet is full of videos of guns firing underwater these days, but the one below is different: the Russian APS (pictured above) was made to be fired underwater. Introduced in 1975, it was meant to give Russian frogmen an offensive weapon underwater. They already had an underwater pistol -- the SPP-1 (pictured below)-- but its range was limited. Under ideal conditions, the APS could hit targets over 30 yards away.
The SPP-1 Underwater Pistol was made in the USSR and issued to Soviet frogmen in 1971. It fired round-based 4.5mm (4.5-inch-long) steel darts from four barrels.
The assault rifle -- a misnomer, because it's smoothbored -- had to be designed with an opening in the rear of the receiver so water displaced by the moving parts could flow out of the action. It fired from an open bolt, too, so the barrel could fill with water, which helps stabilize the "bullets," which were actually darts. The cartridges were a special 5.66 mm round with conventional powder and primer well sealed to function underwater. The magazine held 26 rounds and the gas-operated APS could fire them semi- or full auto.
Although the APS was effective to 30 meters at depths of 5 meters, the deeper you dove, the worse its accuracy and slower it cycled. Down at 40 meters it was effective to only about 11 meters. It could be fired on land but accuracy was terrible and it was very hard on the gun, which was designed to work against the resistance of water.
_The HK P11 was a five-barreled pistol that also fired steel darts (about 3.9 inches long) and was electrically ignited by a battery in the pistol grip._
Our divers were sometimes armed with an H&K P11 dart gun, developed in the 70s. It had five barrels compared to the Russian SSP-1's four, but the barrel assembly had to be sent back to the factory for reloading after every use.
The Russians evidently had us outgunned underwater but fortunately the outcome of the Cold War didn't hinge on which side had the deadlier underwater dart gun.