Echoes in The Depths

By Bruce van Voorst/Washington

Aboard a U.S. attack submarine, a technician suddenly clamps on his headphones as bluish-white symbols dance on the cathode-ray screens before him. He is picking up an eerie metallic message: the echoes of a Soviet submarine nosing through the black depths of the Atlantic 40 miles away. A BC- 10 computer "washes" data through its analyzers and, amazingly, tells the technician not only the type of sub he is hearing but the specific vessel.

This technology, like much else portrayed in The Hunt for Red October, is authentic. The U.S. Navy has the capability to track Soviet submarines with just such precision, electronically gathering underwater sound waves through sonar (sound navigation and ranging). The movie's depiction of a Soviet sub that can run on a superquiet water-propulsion system is not yet a reality. However, Soviet subs have become markedly quieter in recent years (partly because of Soviet espionage on U.S., Japanese and Norwegian propeller technology, which has reduced the cavitation, or spewing of noisy bubbles, from the blades). By some estimates, the Soviets are now able to slip undetected to within 10,000 yds., or torpedo range, of American boats. As a result, U.S. experts are scrambling to develop more sophisticated listening techniques.

The world's ocean depths are already giant audio studios for the U.S. and the Soviets. Both nations have networks of sonar buoys guyed to sea floors and connected by cable to onshore listening stations. Both meticulously map the crucial topography of the ocean bottom. Both continually analyze the thermoclines, or pockets of differing underwater temperature, that deflect and distort sound waves.

To improve U.S. subs' tracking ability, one option is to "go active" by electronically transmitting a "ping" that would locate a target when the sound waves bounce back from it. The problem: echoes from the ping would also disclose the location of the tracker, even if the ping were generated from a third source, such as a buoy towed behind the sub or dangled in the water by a helicopter. The alternative is nonacoustic detection. For example, researchers are exploring ways of sensing a submarine's magnetic field, its thermal radiation or the turbulence in its wake. Some are even studying the bio- luminescence and the scattering of fish caused by a sub's passage. Another approach is radar imaging from orbiting satellites, which may be able to register the minute elevation of the ocean's surface resulting from a sub gliding beneath.

Whatever the technique, the stakes are high. Despite perestroika, Soviet subs still stalk U.S. targets and play underwater cat-and-mouse games with their American counterparts. The hunt continues.