Underwater warfare is one of the three operational areas of naval warfare, the others being surface warfare and aerial warfare. It refers to combat conducted underwater such as: Actions by submarines actions, and anti-submarine warfare, i.e. warfare between submarines, other submarines and surface ships; combat airplanes and helicopters may also be engaged when launching special dive-bombs and torpedo-missiles against submarines.
Seabed warfare is defined as “operations to, from and across the ocean floor.” In general the target of seabed warfare is infrastructure in place on the seabed such as power cables, telecom cables, or natural resource extraction systems..
Humans are not naturally equipped for fighting underwater. While advances in everything from scuba tanks to goggles to underwater vehicles made it possible for people to fight beneath the waves, it has still been hard to put actual weapons into the hands of the people doing the fighting. Underwater rifles, built specifically to launch a projectile through dense water, are one way to arm a submarine soldier, but they present a separate problem: underwater rifles are ineffective above the surface, and a person hoping to fight on land will need to carry a second gun.
To help solve this unique problem, Russia has developed specialized dual-use underwater and above-water rifles. The Russian defense industry is upgrading amphibious guns capable of shooting in the air and underwater. The Soviet Union has led the design for a long time, the Zvezda weekly writes. Soviet engineers develped in 1970s APS rifle and four-barrel SPP-1 pistol for combat swimmers.
They were accepted into service in 1975 and were classified as secret until 1993. APS staged a revolution in underwater arms. TsNIItochmash Institute created an effective and compact weapon. Its range was longer than direct visibility in water. However, APS could operate only in water and was actually useless in ordinary ambient where the range did not exceed 100 meters. Therefore, combat swimmers had to carry both APS and Kalashnikov rifles.
The next stage was the development of amphibious weapons for fighting underwater and on land. In late 1990s, the Tula Design Bureau presented ASM-DT rifle which was a hybrid of APS and AKS-74U. The design allowed firing standard cartridges and underwater “needles”. The magazines for various cartridges had different size. Besides, ASM-DT had a switch from the underwater to the ground regime. There was a water discharge system for fire with “ground” cartridges. Gunpowder gases were discharged through special channels and water was pushed out from the barrel. Despite an original design, ASM-DT was produced only in experimental models, as designers failed to resolve unification problem. A swimmer had no longer to carry two rifles, but he had to carry twice as many cartridges. It was necessary to create a cartridge for effective engagement both in water and on land.
In 2005, the Instrument-Manufacturing Design Bureau offered universal cartridges for underwater fire. PSP cartridge had the same size as standard 5.45mm cartridge. If necessary, it could be fired from a standard gun of the same caliber. PSP cartridges had an unusual form. The edge of the hard-face armor-piercing bullet had a cavity to produce cavitation. An air bubble surrounds the bullet underwater to increase the distance and keep the deadly force. Tests confirmed the effective underwater bullet range of 25 meters. In the air, the initial PSP bullet speed was 330 m/sec which corresponds to the flight speed of bullets for silent guns.
The latest of these is the “dual-medium ADS assault rifle” created by High-Precision Weapons Company, part of Russian defense giant Rostec. With a magazine located behind the trigger and handle (the “bullpup”) configuration, the rifle is compact. Its barrel is fitted for 5.45x39mm bullets, the same kind commonly found in the AK-74 rifle and in use across the world today. In addition, the ADS can load a cartridge of special 5.45x39mm bullets designed to fire entirely underwater. The latest iteration of the ADS rifle appeared at the International Maritime Defense Show in Saint Petersburg, Russia, held in late June 2021.
The new version is now under mass production, making it a somewhat curious weapon. Underwater gunfights are an especially rare kind of combat. Even if they are undertaken by special forces more than regular soldiers, it is still at heart a novel tool for a subset of missions.
Explosive detonations which occur underwater create shock waves in a similar manner to explosions in air. Due to the elastic properties of water, the shock wave tends to be of shorter duration, but with a proportionally larger peak overpressure. The energy in the underwater shock wave attenuates very quickly with range. Therefore, the shock wave from an underwater explosion does not cause the same level of damage as one would expect from studying explosions in air. This is not to say that there are no effects from underwater shock waves.
Depth charges are underwater bombs.
They are set to detonate at a prescribed depth. They must be dropped directly on the submarine to be effective. The primary goal in their use is not to sink the submarine, but rather to take it out of action. The ambient noise created by their use will generally deny the submarine the use of sonar. Furthermore, the shock wave may disable internal equipment that could take the submarine out of action. For example, the shock wave may damage torpedo launching equipment or vital propulsion related machinery. Depth charges are typically either thrown over the side, shot out of cannons, or are rocket-propelled. All methods have limited range and accuracy.
Mine warfare continues to be one of the most effective means to deny use of a particular area to the enemy’s ships and submarines. Mines can be inexpensive and therefore numerous. Mines can detect the target’s presence through three methods: magnetic, pressure, and acoustic influence. Many mines can use all three in any combination. Magnetic influence mines sense the permanent magnetic field causes by the iron in the ship’s hull.
The magnetic field of a ship can be controlled by periodically degaussing the ship. However, this is a time consuming process which involves wrapping the entire hull in large cables and applying a magnetic field for several hours. Most ships therefore have some detectable magnetic field and are vulnerable to magnetic influence mines. Only ships made out of wood or fiberglass are considered immune. Furthermore, the mine can be made to differentiate different types of targets on the basis of their magnetic “signature.”
Mines can also detect targets by the wake they create in the water. As the ship moves through the water, a pressure wave is formed which is visible as a wake on the surface. The same thing occurs underwater but is not visible. The pressure wave can be detected by a mine, however. The faster the ship is moving, the greater the effect.
There are two main types of sea mines in use: bottom and moored. Bottom mines rest on the ocean floor. They can be deployed from aircraft, submarines or ships, although deployment from surface ships is rare. In shallow water they are effective against surface ships and in deep water against submarines.
This phenomenon called supercavitation uses cavitation effects to create a bubble of gas inside a liquid large enough to encompass an object travelling through the liquid, greatly reducing the skin friction drag on the object and enabling achievement of very high speeds. Supercavitating vehicle travelling faster than a passenger jet shall be capable of sailing from London to New York in just five hours.
One of the most innovative underwater weapons developed by the Soviet Union was the VA-111 Shkval (“Squall”) supercavitating torpedo. According to the authors of the journal, “Squall”, which is the first modern weapons using supercavitation is probably the largest breakthrough in submarine warfare since the invention of the submarine itself.
Tula designers developed ADS commando rifle for effective use of the cartridge underwater. It was based on bullpup A-91 rifle. ADS had two regimes: underwater and ground. No change of cartridges was required in contrast to ASM-DT. The underwater regime calls for exclusive use of PSP cartridges, while the ground regime may fire any cartridge. The rifle also had a 40mm under-barrel grenade launcher. ADS can fire 5.45mm cartridges from AK-74 magazine. ADS began test operation six years ago. It was supplied to commando units and combat swimmers in 2019. Gunsmiths said it has major prospects, the Zvezda said.
Now militaries are developing bullets based on supercavitation. Ordinary bullets are designed to travel through the air at speeds greater than half a mile per second. Regular bullets decelerate so quickly in water that they only make it a few feet, which is why diving into a conveniently located pool or waterway when under fire from assassins can be such a good idea. But Norway’s DSG has used the drag-reducing abilities of supercavitation to produce some truly extraordinary projectiles that’ll hit submerged targets up to 60 m (200 ft) away.
When an object encounters a liquid at speeds greater than 100 m/s, the fluid pressure behind the object is lowered below the vapour pressure of the liquid and thus forms a bubble of vapour – a cavity – that encompasses the object, according to a DSG Technology factsheet. Cav-X ammunitions has a cavitating core that in water can form a cavity that exceeds the size of the projectile, so water resistance in the cavity acts solely on the leading edge. Among other things, this allows rounds to enter and exit water more reliably, so a low-angle shot will not ricochet off the water’s surface and endanger friendly or civilian vessels, Garberg said
Since a supercavitating object must create a gas bubble to surround the object moving through water, its been speculated that DSG’s bullets might be harnessing the hot, expanding gasses from burning gunpowder to create the supercavitation bubble.
A supercavitating bullet would be a major addition to the inventories of underwater special forces. Instead of being limited to engaging opponents with knives and hand-to-hand combat, SEALs and other special operations troops would have another weapon in their arsenal.
DSG Technology begins producing supercavitating bullets
DSG Technology has begun production in California of its supercavitating multi-environment ammunition (MEA), which the company said allows for shooting into and under water and better addresses multi-layered targets. The CAV-X Supercavitating Ammunition is classified by the company as a “Multi-Environment Ammunition.” The company says “this projectile is effective against submerged targets and targets in the air.
Garberg said the company can produce rounds in three loads: maximum, medium, and subsonic, depending on the customer’s intended application, which allows users to buy ammunition specifically for a maritime or littoral environment, or specifically to address multi-layered or armoured targets. Depending on the weapon and the used loading variant, this ammunition is suitable for use in partial or fully submerged weapons, regardless of if the target is in water or on the surface.”
This means that larger calibre Cav-X ammunition could be used in defence against torpedoes from surface or submerged platforms. For example, vessels armed with a Phalanx air defence weapon could address an incoming torpedo in the same way it would address incoming missiles, without worrying that the rounds would ricochet off the water’s surface.
The company is working on two types of rounds. The A2 round is shot from the air at other targets in the air or against targets underwater. The X2 round, on the other hand, is designed for combat swimmers and special operations personnel from underwater.
While the Cav-X can be applied to any calibre, DSG Technology said 5.56 mm supercavitating ammunition has a typical effective range of 700-900 m in air and 10-11 m in water, or the sub-sonic load 600 m in air and 12-14 m in water. The 7.62 mm ammunition would have a typical effective range of 1,100 m in air and 20-22 m in water, the sub-sonic load 500 m in air and 12-14 m in water. The 12.7 mm has typical effective range of 2,200 m in air and 60 m water (a sub-sonic configuration is not suitable at this calibre), according to the company.
The supercavitation effect can be produced, rather counter-intuitively perhaps, by giving the projectile a flat, disc-shaped nose with a sharp edge lip. This pushes water out of the way hard enough to leave an air bubble just big enough for the projectile to move through without its sides or back dragging against the water. In the case of torpedoes, boats and submarines, the effect can be enhanced by routing exhaust gases through to the tip so they can add to the air bubble.
DSG says it’s had to turn to the aerospace industry to find manufacturers that can work to the tolerances required for its CAV-X supercavitating bullet designs, which appear to use rounded tips that lead back to flat, sharp ridge discs at the point, as well as other ridges positioned further back on the bullet body. Whatever they’ve done, the results are remarkable. An accurate range of 60 m, still moving fast enough to deliver destructive force, as achieved by DSG’s 12.7x99mm NATO .50 rounds, is unheard of, and it opens up some mission capabilities that have never before been possible.