The current Russian heavyweight torpedoes include the propeller-driven HTP-fuelled 25.6in calibre Type 65, designed to attack US nuclear aircraft carriers and large merchant ships such as supertankers. It is reported that the explosion of one of the latter types was responsible for the loss of the Kursk.
This is the current Royal Navy heavyweight torpedo for anti-submarine and anti-ship use. Spearfish is a 21in torpedo 23ft (7m) long, weighing 4075lbs (1850kg). Powered by a Hamilton Sundstrand 21TP04 gas turbine engine driving a pump jet, Spearfish can reach a top speed of 80 knots over short distances, or run out to 30 nautical miles (54,000m) at low speed. Its Otto fuel II is mixed with hydroxyl ammonium perchlorate, which acts as an oxidiser and improves the specific energy of the fuel. It is guided by wire from the launch submarine, then homes using active or passive onboard sonar, analysing the results in its own microprocessor which allows the torpedo to take autonomous tactical decisions.
Modern homing torpedoes with an anti-surface ship capability use wake-following to acquire and hit their ship target. Sensors in the head of the torpedo, which can be electronically directed upwards, are attuned to detect the edge of a ship’s wake passing overhead, and to recognise the other edge of the wake, where the torpedo is programmed to execute a turn to follow the wake in a sinuous course, biased to the direction where it is narrower — that is, towards the stern of the target ship — until it is close enough to home onto the hull itself and pass beneath the keel to detonate. Other models have been developed which follow the wake directly, and these are the hardest to counter, because of the reduced closing time. A modern example of a wake-follower is the Russian 21in USGT pump-jet torpedo.
To counter wake-followers, defensive anti-torpedo torpedoes have been developed which launch from the target vessel’s fantail (see Part III).
The Russian VA-111 ‘Shkval’ (‘squall’) rocket-propelled torpedo is an interesting development, but its supposed employment raises questions. After ejection from a normal 21in torpedo tube, Shkval quickly accelerates to its underwater cruising speed of some 200 knots. It can do this because the Russians have taken the problem of cavitation suffered by high-speed propellers, and turned it literally on its head, using a bubble carpet system first used on boat-hulled hovercraft in the 1960s and 1970s. By creating and ejecting from its nose a stream of supercavitating bubbles, the Shkval travels in this relatively frictionless medium, and is therefore capable of reaching speeds up to four times faster than older conventional torpedoes.
Touted as a rapid-reaction anti-torpedo defence, at a time when noisy Russian submarines were at risk of attack from the stealthier US Navy boats, it is clear the Shkval can be an effective rapid-response weapon to attack an enemy submarine which its launch boat has detected.
It was originally claimed to be designed to intercept an incoming torpedo and explode it well outside danger range. However, this would seem to be a misinterpretation of its capabilities. Assuming an accurate sonar fix, it could strike an enemy submarine before the latter could manoeuvre out of its way or launch against its own boat, but the very speed that is touted as an advantage is also its principal weakness. At 200 knots, it has no means of homing actively or passively. With even the best current sonar ranging allowing up to 15 degrees leeway, at the Shkval’s maximum range of 12,000yds (11,000m) it would miss by 500yds (450m). The original Russian version had a nuclear warhead, which could still take out a target at that distance. However, how would the Russians have planned to trigger the warhead? For years it has been reported that they have produced a later version which, having reached the vicinity of an enemy submarine at high speed, will of necessity slow down to begin hunting. Of course, once it has acquired its target, there is always the possibility that it will then close at its original high speed to ensure a kill. But this is basically an anti-submarine employment, and the homing version has yet to make an appearance.
Anti-torpedo ability would need precision homing or guidance which the Shkval does not have during its highspeed run. The only way of ensuring destruction of an incoming torpedo at long range would be to provide Shkval with a small nuclear warhead, when the high-speed run is of advantage in distancing the launch submarine from the nuclear blast. Otherwise any modern high-speed torpedo with a nuclear warhead would do the job almost as well, and with the benefit of guidance.
It is thought to use spring-out stabiliser fins, which would need to project beyond the stream of bubbles to have any effect. In the photo of the tail nozzles, the tips of these fins can be seen retracted into the body. At the speed at which it travels through the water, Shkval needs a highly sophisticated rapid-reaction depth control system, as a slight up or down angle could quickly lead it to broach the surface or dive to crush depth. One further drawback is that the supercavitating action is extremely noisy and the Shkval can be detected from long range, allowing the target to launch hard-kill countermeasures and attempt to take evasive action.
LIGHTWEIGHT ANTI-SUBMARINE TORPEDOES
Although all the modern lightweight 12.75in antisubmarine torpedoes have a relatively small warhead, the ability to hit and hole a submarine which has gone deep is likely to prove fatal. And Sting Ray, MU90 and the US Mark 50 have shaped-charge warheads to punch through the spaced double-hulls of Russian boats. Most 12.75in torpedoes are powered by electric batteries, but the US Mark 46 uses an Otto fuel II reciprocating external combustion engine, and the Mark 50 Barracuda has a lithium/sulphur hexafluoride closed-cycle system which is shared with the Japanese GRX-4. The Russians, however, prefer the use of a solid-fuel rocket, for example in their APR-2E anti-submarine torpedo.
The MU90 has been sold to the navies of France, Germany, Italy, Denmark, Poland and Australia. It is the modern 12.75in diameter to fit the NATO standard launch tubes, and is 112in long (2.85m). Capable of diving to 1000m (3280ft), it has active or passive homing. Its electric batteries powering a pump jet enable it to sprint at up to 50 knots. It has an onboard profiling capability which allows it to scan and detect bottomed diesel-powered submarines. EuroTorp has begun development of an anti-torpedo hard-kill version.
Sting Ray is a lightweight anti-submarine homing torpedo to the standard 12.75in calibre, which entered service with the Royal Navy, the Royal Air Force, the Norwegian and the Thai navies. Powered by magnesium/silver chloride batteries driving a pump jet, it is capable of speeds up to 45 knots, and homes using active and passive sonar.