« em: Abril 21, 2006, 12:42:31 pm »
In my recent “Conventional Global Strike” I promised to address soon other ways in which U.S. Navy submarine armament systems are dramatically broadening in reach and lethality. But observing the errors of fact and occasional tone nearing hysteria in some media lately, I feel compelled to first address an “enemy” weapon and put it in its proper place. This weapon has been called in print “hellacious.” It's been described as a “quantum leap” in the nature of naval warfare from this day forth -- a disruptive technology for which America is woefully unprepared. It's even been said that there's no physically possible friendly defense against it, and the target won't even realize the weapon is coming until it impacts and the target's crew are dead. Paints a scary picture, doesn't it? Yet none of these statements are true.http://www.military.com/soldiertech/0,14632,Soldiertech_060420_shkval,,00.html
The weapon is the famous (or infamous) Russian VA-111 Shkval rocket torpedo and its variants, capable of speeds of more than 200 knots underwater. This speed is achieved by the rocket pushing the sharply tapering, flat-tipped torpedo so fast that a vacuum bubble forms around the body of the weapon, greatly reducing water resistance -- the process, for the uninitiated, is called supercavitation.
The Shkval has been getting a sudden flurry of news attention. I suspect some of this is due to Russia selling the Shkval-E export version to China -- newly identified by the Pentagon as an emerging peer competitor in the western Pacific if not globally. Those sales actually date back to at least 1998. Then there's Iran's very recent test of a ship-launched supercavitating torpedo. Given allegations that Moscow sold a few prototype Shkvals to Tehran, it appears likely that the Iranian weapon has roots in Russia's design.
More properly, I should say “the Soviet Union's design,” because -– despite certain misconceptions to the contrary -- the first Shkvals entered service at the height of the Cold War, after a decade in development, back in 1977. That's almost thirty years ago. Since America's Submarine Force and other intelligence assets in those days kept very close tabs on Moscow's naval weapon tests and exercises, Washington's defense establishment has been well aware of supercavitating torpedoes for a entire human generation. That the U.S. Navy chose not to develop and field such weapons years ago says something, not about a lack of ability as some writeups have insinuated, but about a lack of desire. I'll return to this later in the discussion. (The Navy and DARPA do slowly continue R&D into possible supercavitating projectiles and vehicles for specialized purposes, but these remain paper concepts or in the early test-apparatus stage.)
Among errors of fact that one might have read in a newspaper or on-line news digest, or even seen in a TV documentary, is that Shkval-type weapons move faster than their own noise. This makes them totally undetectable to their victim -- a Virginia-class sub is sometimes mentioned in this context as a choice target -- until the rocket torpedo detonates and the American sub is destroyed. There's just one serious problem with this, not for the Virginia-class sub but for the enemy. The speed of sound in seawater varies subtly with local conditions, but is typically just under one statute mile per second -- five times the speed of sound in air, for comparison. This makes the speed of sound in seawater about 3,000 knots. A supercavitating weapon doing 300 knots is barely making Mach 0.1 in the medium in which both it and its target are located. And rocket engines are terribly noisy. That noise signature will travel on ahead of the Shkval to be heard by a submarine's passive sonars well before weapon impact. As detailed below, (and despite bellicose Iranian claims to the contrary), American submariners have an ample toolkit for swiftly throwing off the Shkval's aim, and then fighting back.
So much for that bit of disinformation.
Iran isn't about to give up easily in their war of words (and associated psy-ops) about their new wonder-torpedo. They allege it's “sonar evading.” If you know very much about sonar, you have to be scratching your head and asking, What the heck is that supposed to mean? I tag it as agit-prop doubletalk -- better laughed at than worried about. I justify my tagging as follows:
Sonar evasion per se, by any weapon or vessel, is achieved in one of two ways. The first is to be very quiet, so your target's passive sonars can't detect your presence nearby. Scratch that, since supercavitating rockets are deafeningly loud -- the vacuum bubble collapses in the turbulence of their engine exhaust, providing scant sound isolation if any at all. The second is the old, familiar use of sonar layers and other underwater noise propogation effects to mask your acoustic signature from the target as you approach. But no one understands these effects better than the U.S. Navy, and not just subs but surface ships and aircraft are equipped to leave no room for a roaring rocket motor to hide. (Surface combatants can stream variable-depth sonar towed arrays, and their supporting anti-submarine helicopters can use variable-depth dipping sonar and also drop optimized patterns of sonobuoys.) Besides, in the littorals (shallow and/or near-shore waters), where near-future naval battles seem most likely to occur against enemy diesel subs or small surface craft deploying any large weapons, there often is no sonar layer -- the water isn't deep enough for one to form. With up-to-date and thorough hydrographic data in hand (including salinity variations, charted and uncharted wrecks, gas- and oil-drilling/pumping noise sources, and water transparency or lack thereof), American and allied subs would sneak in where undersea conditions maximize their own stealth, while they use the same knowledge to seek and ambush enemy subs.
(Purists will note there is a third way to achieve low observability against active pinging sonar, namely the use of anechoic -- sound absorbing -- coatings on the hull. But modern U.S. submarine passive sonars are able to derive the range to any high-decibel sound source instantly, obviating the need to ever go active against an inbound torpedo. The implied analogy to radar-absorbent materials on cruise missiles fails underwater.)
So much for “sonar evading.”
To best appreciate these issues, it's important to think of the bigger picture. Superior U.S. Navy sonars (and the skilled sonar techs who use them) in any theater of conflict or combat will constantly be hunting for the slightest hint of enemy threats. And an incoming Shkval has to come from somewhere -- it doesn't materialize out of thin air. The best strategy, as always in naval warfare, is to destroy the enemy platform before it can fire its weapons effectively. Special new active and passive sonars, advanced signal processing algorithms, and console display modes so sophisticated they're classified are intended to eke out the slightest whiff of an enemy diesel sub concealing itself amid the naturally high background noise to be found in most littoral areas. The same thing goes for enemy fast-attack craft rushing along or lurking on the surface.
In many littoral warfare scenarios an American sub won't be operating alone, but rather as part of a joint (or combined, i.e., allied) task force that would include other subs, unmanned undersea vehicles, temporary bottom-moored listening grids, surface warships, aircraft (including recon drones), plus intermittent overpasses by surveillance satellites. Network-centric warfare is a complicated team sport. With recent and impending breakthroughs in “comms at depth and speed,” submarines are now part of that team, and the task force would literally cast a wide net to localize, track, target, and sink any threats. In the earliest, “battlespace preparation” phase of some armed showdown, a lot of attention would be paid to accounting for and neutralizing all potential Shkval-launching platforms.
The point of the discussion, so far, is that speed of one weapon, viewed alone, doesn't determine the outcome of either a sub-on-sub dogfight or a major naval engagement. The fact that the maximum range of a Shkval or derivative, before its rocket fuel runs out, is only four or five miles, should help put in proper perspective that supercavitating torpedoes are hardly as “hellacious” as they've been described. (By the way, their disadvantages hold equally well if carried on enemy nuclear subs as if carried on enemy diesels.)
Perhaps one good proof of this is that active duty submariners I've met on subs or talked to at conferences aren't exhibiting any panic over Shkvals. The way they describe it, the latest mod of the Improved Advanced Capability (ADCAP) Mark 48 sub-launched heavyweight torpedo remains by far their weapon of choice. They scoff at the threat that a Shkval would pose -- assuming it isn't armed with a nuclear warhead. (In that nightmarish scenario, the Shkval with its limited range would amount to a suicide weapon. And Mark 48s are nuclear-capable, if necessary, too.) In contrast to the Shkval, the latest Mark 48 is reported to have a maximum range of some 30 nautical miles. During a game of cat-and-mouse, this means the American sub can threaten anything inside an area 36 times as big as what's covered by a 5-mile-range Shkval. That gives a very significant, classic tactical advantage: By holding open the range using the nuclear submarine's maximum speed advantage over the diesel's (say, 30+ knots sustained compared to 20ish in short bursts), the American vessel can “bombard” its opponent from outside the diesel's ability to hit back with Shkvals. Furthermore, the maximum speed of a Mark 48 is reported in open sources as some 60 knots, and I suspect that the actual (classified) figure for the latest (ninth?) mod might be several knots higher than that. The American weapon is three times as fast as the enemy diesel -- and is also much faster than any known nuclear sub. (One news source claimed that the U.S. Navy had failed to invest in good torpedos for years now, and that our best fish were so slow that enemy subs and ships could simply outrun them. I have never read a more incorrect statement in my entire 10-year career as a non-fiction submarine commentator.)
Granted, Iran's rocket torpedo is three times faster than the latest Mark 48, but I've tried to show above that in the wholistic framework of modern naval action, out in blue water or in the littorals, a factor of three in weapon speed makes a difference in degree but most certainly not a difference in kind. Yes, better situational awareness, and faster reaction time, are at a heightened premium aboard American ships and subs in the emerging environment. It's precisely these attributes that the Navy is striving with a will to enhance in every possible way. (The revolutionary layout of the Virginia-class control room is just one example of many in this arena of man-machine interfaces for optimal warfighting preparedness and survivability.)
But there is a difference in kind between a Shkval and a Mark 48. The Mark 48 is wire guided, allowing fire-control technicians to adjust the fish's course for weaknesses in the original firing solution (think torpedo “Kentucky windage”), or to compensate for evasive maneuvers by the target. Technicians can also use their submarine's powerful sensors to help discriminate between the genuine target and any decoys or noisemakers the target might launch -- all assuming the wire doesn't break. Even if the guidance wire does break, the latest Mark 48s have such capable active and passive sonars and on-board computer brains that they can search on their own, pick out their intended target from amid littoral (or other) acoustic clutter while ignoring neutral vessels nearby, and then zero in for the kill.
In contrast, most supercavitating weapons that are operational right now are pretty dumb. This is mainly because their ancestors started out as dedicated nuclear weapons, so that pinpoint accuracy wasn't much of an issue to the engineers and commanders who built and deployed them. Speed was the design bureau's sole object (because conventionally-powered USSR torpedoes in the late 1960s were slow). Given this dubious legacy, most high-explosive-armed Shkval-like torpedoes still rely on traveling in a straight line, with no guidance or homing whatsoever after launch. Nowadays, the firing vessel hopes that this straight line intersects the target's track at the same moment that the target happens to be at that point on its track. This is like early World War II technology! A well-aimed spread of such weapons could definitely prove fatal to a big surface ship, say one of our supercarriers, and higher torpedo speed does make up for softness in the firing solution. But as mentioned above, the key to successful defense is to prevent the Shkval's launching vessel from getting close enough to the carrier to begin with. This is presumably one driving force behind the U.S. Navy's greatly stepped-up emphasis on anti-submarine warfare for surface battle groups -- with enemy diesel subs receiving particular attention, their roles played by allied diesels including the leased Swedish Gotland-class sub and her crew. At this point American submariners have been engaging in anti-diesel exercises for some time; after a few initial humbling setbacks, the U.S. side collectively developed doctrine and tactics that give them a much better edge. (For a take on the relative disadvantages of modern diesels with air-independent propulsion, compared to nuclear-powered subs, see my archives for “Diesel Downside,” 13 July 2005.)
American submariners tell me that all they need to do when faced with an incoming high-explosive Shkval is make a slight change in depth (or a fast change in heading and speed), and the Shkval will go right by, its impact or laser-proximity fuse left with no reason to explode within dangerous range. It's very beneficial to be able to move in three dimensions, even or especially in the littorals!
Of course, as with all weapons down the ages, Shkval-type technology isn't standing still. Russia is developing a version of a supercavitating torpedo that does have some artificial intelligence and homing sensors including sonar. The problem is that for the sonar to work, the Shkval has to slow down drastically, in spurts, so it won't be blinded by its own noise and has a chance at acquiring and reacquiring its prey to make the needed terminal course corrections. This seeming enhancement to the Shkval introduces a substantial Achilles' heel: When moving slowly, and relying on conventional sensors to home on its target, the Shkval becomes vulnerable to all the standard evasive tactics and countermeasures with which American submariners are exceedingly well versed. The Shkval, during such an attack, also repeatedly forfeits its one apparent advantage, its speed, before having to accelerate again. Rumor has it that Moscow is trying to make a wire-guided Shkval, but trailing a wire that doesn't snap at 300 knots, or melt in the searing heat of the rocket exhaust, or cause the vacuum bubble to collapse enough for the whole weapon to suddenly tear itself apart, seem daunting problems indeed.
Counterattacking the Shkval's launch platform is best done with a Mark 48 or two. The answer is definitely not for our Silent Service to rush and clone the Shkval. This is another overwhelming benefit of our current conventional torpedoes: They can be launched very quietly, be programmed to run on a dog-leg course initially at slow and quiet speed to disguise their point of origin, and then attack the Shkval's parent platform with ease -- because the launch signature and trajectory of the Shkval will point right back to its own point of origin. The American submarine, in contrast to the Shkval shooter, can shoot back while retaining good stealth. With the latest integrated combat systems, if ever caught by surprise our guys can get their retaliatory fish into the water in a matter of seconds. Then using superior technology and tactics, the American sub can regain the initiative and go on the offensive. (Speed of opening accurate counter fire can be more important than transit speed of the weapon itself.)
I don't mean to downplay the risks of major naval combat against a well-equipped, well-trained, determined competitor, or of naval guerilla warfare by a rogue state. (Iran dueled with us in the “Tanker War” in the Persian Gulf in the 1980s.) I've warned in earlier essays that if battle at sea does erupt some day, our nation needs to be mentally and militarily prepared to lose some ships and Sailors -- just as the Royal Navy did in the Falklands Crisis in the early ‘80s.
Previously in thie piece I stated that the Shkval isn't, as claimed, completely immune to friendly defensive weaponry. This is because, for years, the U.S. Navy has been investing in, developing, and testing undersea weapons that really do move at Mach 1 or faster in seawater. In contrast, the Shkvals and their ilk, which weigh several tons and can be close to 30 feet long, come up against a practical speed limit. Once supercavitation is achieved, water friction drag is significantly reduced, but some drag is always still there. That's why a Shkval hits 200 or 300 knots and then stays at that terminal velocity, instead of going faster and faster till it takes off for outer space, so to speak. Universal formulas apply for the power needed to increase speed of a given body moving through a given fluid with a given drag coefficient. The basic stricture is that the increase in power goes up with the cube of the desired increase in speed. According to this formula, to get a 300-knot Shkval to go 10 times as fast and be truly supersonic would require 10 x 10 x 10 = 1,000 times as much power. You never know, but I don't see this happening soon. (Talk of underwater jet engines that burn liquid aluminum for fuel will remain the stuff of science fiction for quite a few years.)
So what are the true Mach 1 weapons America is working on?
One of these devices is an anti-torpedo dart, fired underwater by an sonar-aimed gun in a streamlined turret. In a proof-of-concept experiment several years ago, the Naval Undersea Weapons Center Newport Division was able to shoot a dart in a tank at greater than the speed of sound in the surrounding water. Though the dart is not self-propelled, and thus loses velocity (and accuracy) with range, as a close-in defense system against fast (and not so fast) enemy torpedoes it holds great promise.
The other device that's been discussed for a while in the unclassified literature is a hull-mounted pressure-wave generator. (Think of something like an active sonar array that sends out a tremendously strong burst of noise.) The pressure-wave generator transmits an intense underwater focused shock wave in the direction of an inbound torpedo. Since shock waves automatically move at the speed of sound, this provides a genuine Mach 1 countermeasure against any Shkval. If the pressure wave is aimed well and the timing is just right, a “hellacious” wall of acoustic energy will smash the Shkval to pieces. (The Shkval's higher speed makes the collision all the more violent!) This device is ideal for mounting on the hulls of all-electric surface ships, such as the DD(X)/CC(X) fleet of the future, and maybe LCSs and even subs too.
If you're really feeling the need for speed, think about these developmental supersonic underwater weapon systems. They outclass the Shkval by a factor of ten.
Some urgency is called for regarding such advanced defensive measures, as supercavitation technology is quickly proliferating among America's actual and potential foes. But at the same time it's crucial to recognize that the Shkvals of the world have been surrounded in a fog of plain untruths and insidious rhetoric. What concerns me most is not the supercavitating weapons themselves -- as I say, they've existed for decades. Their sensationalized treatment in pockets of the media give domestic nay-sayers further ammo to press their case in the most absurd and self-destructive claim of all, that America's current nuclear submarines are nothing but Cold War relics -- now, because they're supposedly hopelessly vulnerable to Shkvals. This essay has attempted to show that it's the Shkvals that are the real Cold War relics. So long as they're deprived of their nuclear warheads, against a properly trained and equipped U.S. Navy their speed is their own greatest weakness.