Underwater firearm

An underwater firearm is a firearm designed for use underwater. They are in the arms inventories of many nations. A common feature of underwater firearms or needleguns is that they fire flechettes or spear-like bolts fired by pressurised gas, instead of standard bullets.

Underwater firearms were first developed in the 1960s during the Cold War as a way to arm frogmen.

Because standard bullet ammunition does not work well underwater, a common feature of underwater firearms is that they fire flechettes instead of standard bullets.

The barrels of underwater pistols are typically not rifled. Rather, the fired projectile maintains its ballistic trajectory underwater by hydrodynamic effects. The lack of rifling renders these weapons relatively inaccurate when fired out of water. Underwater rifles are more powerful than underwater pistols and more accurate out of water, but underwater pistols can be manipulated more easily underwater.

Among the many engineering challenges in designing underwater firearms is that of developing a weapon which can be effective both underwater and out of water. The ASM-DT amphibious rifle is an early example of such a weapon. First fielded by the Russian special forces in 2000, the folding-stock ASM-DT amphibious rifle is capable of firing two kinds of ammunition, both of 5.45 mm caliber:

When used against underwater targets, an underwater firearm may have a longer range and more penetrating power than spearguns. This is useful in such situations as shooting an underwater intruder where the projectile may have to first penetrate a reinforced dry suit, or a protective helmet (whether air-holding or not), or a thick tough part of his breathing set and its harness, or the plastic casing or transparent cover of a small underwater vehicle.

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