US seeks ways to use aquatic `weather' to hide its submarines. Navy expanding research program for oceanography

For submarines as well as tourists, the Mediterranean in summer is a fine place to escape. That's because the shallow sea, warmed by long hours of sun, acts like a blanket of insulation.

Sound produced by subs is trapped near the bottom, making it easier for them to hide from the prying ears of anti-sub ships and planes.

In the shadow war underneath the seas, advantage may sometimes lie not with the most expensive electronics but to him who best understands the secrets of the deep.

The US Navy, under Secretary John F. Lehman Jr., is thus showing a new interest in ocean research.

By the mid-1990s, Navy subs might be able to hide behind ocean phenomena as if they were hiding behind a mountain range.

Toward that end, the Navy on July 2 announced it was endowing four chairs in oceanography at academic institutions around the United States.

This move comes on top of an expansion of the Navy's own ocean-study facilities at Bay St. Louis, Miss., and Monterey, Calif.

Much of the Navy's study in this area aims to analyze ocean structure, which has turned out to be far more complex than thought 20 years ago, say Navy officers.

Where once scientists believed the ocean was a still mass striped with river-like currents, such as the Gulf Stream, they now know it contains high and low pressure fronts, and giant swirling eddies.

In effect, the open ocean has ``weather,'' just as the atmosphere does, says Capt. Ernie Young, an oceanographer with the Office of Naval Research. And changes in this weather greatly affect how the sound waves produced by subs travel through the water.

Salinity, shape of the bottom, and particularly water temperature can block sound, or distort it.

Crewmembers on US P-3 Orion antisubmarine planes, which patrol the oceans listening for Soviet underwater activity, routinely tell of subs disappearing suddenly from their screens.

``In many instances, you should be detecting this guy galore, and you're not sure why you aren't,'' says Captain Young. ``Many times you detect, and you're not sure how it happened.''

Soviet subs, relatively noisy today, are expected to become much more quiet in coming years, as the USSR perfects the silencing techniques already used by the US.

Knowledge of ocean ``weather'' will thus become an increasingly critical aspect of antisubmarine warfare, notes Young.

With a thorough understanding of ocean conditions, a US plane or vessel can pick the right direction and depth to listen for Soviet subs. It can set its sonar to listen for the frequency most likely to reveal an adversary's position.

A US sub could use such knowledge to cloak its own movements -- diving into an eddy, perhaps, to muffle its tell-tale trail of sound.

As advances in technology allow weapons to be fired at greater and greater distances from their target, ocean information might also help ``smart'' torpedoes guide themselves, Young says.

Though Secretary Lehman has been pushing development of Navy oceanography, the service has a long way to go if individual vessels are to turn the ocean to their advantage by the 1990s.

Today the Navy receives only some 600 samples of ocean data daily. Forecasting water conditions accurately would require thousands of such data points every day.

New satellites would have to be launched to augment N-ROSS, the Navy remote ocean-sensing system. Navy oceanographers would need underwater sensors, research ships, and expensive new computers to reach their goal: daily forecasts for those areas of the ocean where subs tend to lurk.

``It's certainly not too ambitious a goal,'' says James Luyten, an associate scientist at the Woods Hole Oceanographic Institute. ``But I'm not sure whether they'll be able to do it.''