Scientific American

May 2001 issue

Warp Drive Underwater

By traveling inside drag-cutting gas pockets, new subsea systems can move much faster underwater than their conventional counterparts on the same amount of energy

By Steven Ashley

When the Russian submarine K-141 Kursk sank last August, rumors rapidly arose that the mysterious blasts that sent the big boat to the bottom of the Barents Sea were connected to testing of an ultrahigh-speed torpedo. Several months earlier, when American businessman Edmond Pope was arrested in Moscow on charges of espionage, it was said that he had been trying to buy the plans for an ultrahigh-speed torpedo. Although the details surrounding both the tragic naval accident and the celebrated spy case remain unsettled, evidence does suggest that both incidents revolved around an amazing and little-reported technology that allows naval weapons and vessels to travel submerged at hundreds of miles per hour - in some cases, faster than the speed of sound in water. The swiftest traditional undersea technologies, in contrast, are limited to a maximum of about 80 mph.

Of late, it has become increasingly apparent that the world's major naval powers are developing the means to build entire arsenals of innovative underwater weapons and armadas of undersea watercraft able to operate at unprecedented speeds. This high-velocity capability - a kind of "warp drive" for water - is based on the physical phenomenon of supercavitation. This fluid-mechanical effect occurs when bubbles of water vapor form in the lee of bodies submerged in fast-moving water flows. The trick is to surround an object or vessel with a renewable envelope of gas so that the liquid wets very little of the body's surface, thereby drastically reducing the viscous drag. Supercavitating systems could mean a quantum leap in naval warfare that is analogous in some ways to the move from prop planes to jets or even to rockets and missiles.

Although current funding levels for supercavitation research are said to be modest (around $50 million in the U.S., for example), the list of potential supercavitating weapons and naval vessels is extensive and altogether startling. It includes high-speed underwater bullets aimed at mines, homing torpedoes, boats - even low-flying aircraft and helicopters - from submerged gun-pods that look like the turrets on World War II–era aerial bombers. Other possibilities include high-velocity antiship and antitorpedo torpedoes and "midrange unguided engagement breakers," which are larger weapons intended to force an end to a conflict between two submarines. Also envisioned are small, superfast surface craft as well as nuclear-capable subsea missiles designed to neutralize entire aircraft-carrier battle groups.

Some naval experts believe that supercavitating systems could alter the nature of undersea warfare, changing stealthy cat-and-mouse stalking contests between large submarines into something resembling aerial combat, featuring noisy high-speed dogfights among small, short-range "subfighters" shooting underwater bullets at one another after having been launched from giant "subcarriers."

Other experts point to the possibility of fielding long-distance, multistage supercavitating torpedoes/ missiles fitted with nuclear warheads ("long-range guided preemptive weapons") that could prove to be a relatively cheap and effective counter to future "Star Wars" missile defense systems. These devices could dash in from many miles out at sea entirely underwater, pop out of coastal waters close to their targets, and drop their lethal payloads before any aerial or space-based defenses could react.

Surprisingly, we now know of at least one supercavitating weapon that has existed for many years. In 1977, after more than a decade of research and development, the Soviet navy secretly introduced a rocket-powered torpedo called the Shkval (Squall) that can "fly" through water at 100 meters per second (about 230 miles per hour) or more inside a self-generated gas cavity. Although this nuclear-tipped underwater missile is in some ways a bit crude and less than entirely effective, news of it in the early 1990s forced the Western military powers to take notice of supercavitating technology.


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