Monday, 3 April 2006

Storm Squall in a Teacup

From the ABC :
Iran has test-fired a sonar-evading underwater missile that can outpace any enemy warship, a senior naval commander told state television on Sunday during a week of war games in the Gulf.

Western nations have been watching developments in Iran's missile capabilities with concern amid a stand-off over the Iranian nuclear program, which the West says is aimed at building atomic bombs.

Iran says the program is only civilian.

State television in Iran earlier described the missile as the world's fastest.

"This missile evades sonar technology under the water and, even if the enemy sonar system could detect its movement under the water, no warship could escape from it because of its high velocity," Revolutionary Guards Rear Admiral Ali Fadavi said.

"The Islamic Republic is now among the only two countries who hold this kind of missile. Under the water the maximum speed that a missile could (usually) move is 25 metres per second, but now we possess a missile which goes as fast as 100 metres per second," he told state television.

The commander uses the word "missile" in Farsi, rather than "torpedo".

"The boats that can launch this missile have a technology that makes them stealthy and nobody could recognise them or act against them," he added.

Iran's ambassador to the International Atomic Energy Agency (IAEA), Aliasghar Soltaniyeh, says the missile test should not worry the world.

He says that, to his knowledge, the weapon could not carry a nuclear warhead.
To His Knowledge. Pardon me if I'm less than impressed.

This beastie looks very much like the export version of the VA-111 Shkvall (Squall in Russian) underwater rocket. Whether bought from Russia, second hand from China, or reverse-engineered I'm not sure, but almost certainly the writing on the side is in Cyrillic not Arabic.

Shkvall TorpedoIt's quite a clever idea : instead of ploughing through the water, it creates it's own "bubble of cavitation". Try to move a flat disk the size of a saucer, flat side on, at 300 km/h through the water, and you'll find it makes a low-pressure cavity behind it, quite a big one. If behind the saucer you put some gas jets to shape the cavity, you can stick quite a large rocket in it. So the power needed to propel the thing isn't the usual power needed for a 3-ton torpedo, it's the power needed to propel a saucer. That's quite a lot, of course, you really need a huge rocket, but still it's a neat trick. Quite in keeping with the Russian tradition of Weird Weapins Systems, some spectacular failures such as the flying tank, some good ideas badly executed, such as their pioneering of paratroops, some winners like anti-ship cruise missiles.

As for sonar detection - well, rockets are not exactly known for being very quiet. The problem, if any, is that it's too loud, it may swamp sensors more accustomed to listening for very subtle variations, much as a microphone designed for detecting a piccolo at the back of the theatre might not perform very well if a hundred jackhammers were being used instead.

It's not exactly a "secret weapon", having its own entry on wikipedia.

Early models were unguided - fire and hope they run straight. Later models had an autopilot, so although they had no actual homing, at least you had some assurance they'd go in a straight line, hopefully towards the target. It's thought that the latest production models did a "sprint and drift", zipping out to the general target area, getting a swift course update, then going full bore again.

OK, so what is it used for? Well, with a smallish nuclear warhead, it's a good anti-sub weapon. If you detect an incoming torpedo from a previously undetected enemy sub in a particular direction, fire one of these to its maximum range in that direction, and odds are the enemy's in a world of trouble - as is the incoming torpedo. Of course, the odds of your own sub surviving may not be that good either: but probably better than sharing your personal space with a Mk48 torpedo marked "made in the USA".

The usual quoted range though is only 7 km, about 4 miles. So to use it against ships, you have to be uncomfortably close, and if it only has a conventional warhead, it won't be much good against subs. This is because of back-pressure : at too deep a depth, the rocket is fighting lots of external pressure, won't work as well, the cavity is more difficult to form, and it just won't work. Without a homing mechanism, and without knowing the depth the target sub is at, the odds of a hit are slim.

So why was it invented? I speculate as follows: at one time, the USSR had a submarine class called the Alfa (Projekt 705). These subs were small, very, very fast, very, very noisy and insanely dangerous to operate. I speculate that their tactics would have been to say "damn the torpedos" - which they could largely outrun - and come in at high speed, caring not a whit about stealth, go to periscope depth, fire a brace of shkvals, and maybe escape during the resultant confusion.

It might have worked : but they used Liquid sodium (or possibly lead-bismuth later) as a coolant. They had to, to get the low weight and high speed. Well, you know from high school chemistry what sodium does in contact with water. It does the same sort of thing to most metals too. Liquid sodium is hellishly corrosive, and highly radioactive liquid sodium leaking from the coolant system was such a problem, even the Russians gave up trying to make this idea work. It wasn't just the number of crews it killed or injured, it was that after each month-long patrol, the boat would have to spend years getting decontaminated so they could try to make it work again.
Series production of the Project 705 boats began in the mid-1970s, and the program ended in 1983 with the sixth production unit. Eventually four of the seven Project 705s were lost due to reactor failures. One boat was retired by the end of 1987, and four others were decommissioned in 1990-1992.

So now it's a weapon for small, fast attack boats and shore installations, so hordes of fast torpedo boats would sally forth against a carrier group, and the few that survive to get within 4 miles fire these things off. Once in the water, they'd be difficult or impossible to intercept, and you'd only have a minute to change course, just as if a normal torpedo had been fired at 1 mile. Fire enough in a converging pattern, and some would hit.

Russia has openly offered the Shkval for sale at international arms shows in recent years. Though few in the West have witnessed the Russian Shkval missile in action, several expert sources have seen a marketing video distributed to potential buyers. As one described the scene: "First of all, you only see the Shkval from the rear; you don't get to view the front of the torpedo where all the interesting stuff is--the cavitator, the ventilation ports, and so forth. The scene opens with the Shkval being launched off a patrol boat. After it drops below the surface there's an extended pause, when without warning, there's a bright flash in the water and you sense some commotion underneath the waves. After a short time, a triangular trail of bubbles starts to appear at the surface and moves off into the distance at a good pace. Meanwhile, not much else happens until all of a sudden, you see a little explosion way off on the horizon, followed by the delayed report. It's pretty amazing to see how far the thing has gone in such a short time."

Then you have a 3-ton piece of ironmongery hitting the ship at 300 km/h. Then the warhead goes off, but the real problem is any unburnt rocket fuel. That burns hot, and water won't put it out. Having a few hundred liters of this stuff sprayed about your ship is Not Good, especially for a carrier with lots of fuel lines, bombs and such.

Of course, if you have a little handling accident on board the launcher, things could get unpleasant. This may be the cause of the loss of the Kursk

So providing the USN sends its carriers to within spitting distance of the shore, this would be a problem. Too bad they lurk a hundred km or more off the coast, surrounded by a picket of destroyers, cruisers, and aircraft, each one capable of taking out ten or more torpedo boats without raising a sweat. Now a diesel sub might do it - but as long as the CV keeps its peed up to 20 knots or so, the diesels can't keep up and remain quiet. If they go noisy, they die.

As for firing these from a shore installation - there's a far cheaper and easier way of delivering over 4 miles not just one big chunk of explosives that's difficult to intercept or evade, but hundreds of smaller chunks, far faster, more accurately.

Perhaps you might have heard of it. It's called a "gun".

So overall, it's a Storm, or rather, a Squall in a teacup.

No comments: