Copters Rated Second Best in War on Mines

WASHINGTON —  When the Navy dispatched eight helicopters to the Persian Gulf last week to search the treacherous waters for mines, it was relying on what virtually all experts regard as only the second-best minesweeping technique.

The best minesweepers, by all accounts, are still ships.

“So far, I don’t know of many, in fact any, real mines that helicopters have found,” says a retired admiral who once commanded a fleet. “Lots of training mines, but they still haven’t demonstrated that they can find real ones.”

Ships can--in fact, technological advances have greatly improved their ability to detect mines. But unfortunately for the United States, its new generation of minesweeper, two years behind schedule, is only now undergoing trials in the Great Lakes; the first one will not be commissioned for another two months.

Mines, which on a cost and weight basis are probably the most destructive of all naval weapons, also have gotten better.

Although the mine that blew a hole in the side of the tanker Bridgeton on July 24 was of a type first made in 1908, some modern mines can be tuned to detonate only when they hear certain sounds--the propellers of a ballistic-missile submarine, for example.

The current scramble by U.S. officials to cope with the mines in the Persian Gulf as part of the Administration’s effort to protect Kuwaiti oil shipments from the Iran-Iraq War illustrates the complexities of the modern cat-and-mouse game between minesweeping technology and the many versions of one of the oldest tools of naval warfare.

Asked how mines can be countered with even the best equipment and strategies, a former officer on a minesweeper replied: “Very, very carefully.”

The type of mines threatening ship traffic in the gulf are primarily explosive-filled balls with spikes; the spikes contain fuses that detonate the whole package on impact with a ship. Primitive versions were used extensively in the Russo-Japanese War of 1904-05, and improved models being used in the gulf have been manufactured recently in North Korea.

Other kinds of mines are triggered by the abrupt decrease in pressure under a ship’s hull as it passes over the device, by the magnetic field of a ship’s metal bulk or by the noise created by a passing ship. The sound “signature” of a ship varies with number and configuration of its propellers.

A chief reason for the delay in the production of the new U.S. minesweepers is the severe shortage of shipbuilding craftsmen to make the vessels’ wooden hulls, which do not produce the dangerous, mine-triggering magnetic fields that metal ship hulls do.

The various types of mines can be free-floating, moored under the surface by a cable to the sea bottom, or buried on the bottom.

With explosive charges ranging from 500 to 2,000 pounds of TNT, all take advantage of the excellent properties of water as a conductor of shock waves to deliver a blow to a ship’s relatively vulnerable underside.

The mine that struck the Bridgeton as it was being escorted by U.S. warships through the gulf on the first U.S. sea guard mission for the Kuwaitis was a moored mine containing 1,000 pounds of explosives that had broken free of its cable and was floating about 20 feet below the surface.

Naval authorities prefer using special ships to combat mines largely because they can carry a wider array of mine-detection equipment than helicopters and can stay continuously on station for weeks. Helicopters can operate for about two hours at a time.

But for years the Navy’s planners have concentrated on warships with an offensive capacity, and that contributed to a neglect of such defensive vessels as minesweepers.

The new minesweeper models have advanced side-looking sonars that send out sound waves to detect mines. Devices that mimic the magnetic field and noise “signatures” of passing ships can be used to set off the underwater weapons harmlessly.

But most of the Navy’s minesweeping--there are three minesweepers in active service and 18 others in reserve, all built in the 1950s--is done with special “rigs” towed behind the minesweeping ship or helicopter.

There are “mechanical” rigs, consisting of a network of long wires designed to cut mines’ mooring cables. Explosive cutters snap the cables and allow the mines to float to the surface where they are donated by rifle fire.

And there are “influence” rigs, consisting of a long electrical cable that creates magnetic fields that detonate magnetic-sensitive mines, or project noise to set off acoustic mines.

Mines keyed to water pressure changes are a more difficult problem.

“From the surface, the only way I know of setting off a pressure mine is by going over it with a ship,” said one ex-minesweeper officer, “and you don’t want to do that.” Fortunately for minesweepers, these mines have limits that make them useful mostly in shallow waters and susceptible to being set off by passing fish.

Even with the best equipment, minesweeping is still dicey. Bottom mines may be disguised as harmless objects “like a discarded refrigerator,” a Navy spokesman said. And sometimes, the only way to properly identify or detonate a mine is to send a diver down.

In the approaches to a Kuwaiti harbor two weeks ago, about 10 moored mines located by Saudi minesweepers had to be disabled by Navy Seal diver teams, Pentagon officials said.

With no minesweeping ships available in the region, however, the U.S. forces in the Persian Gulf will be relying on helicopters.

Naval experts say there are some advantages to these aircraft, even if their range is limited by fuel capacity. They can be deployed to distant trouble spots more quickly and they can also work faster.

However, the helicopters are largely untested. “We still don’t know what happens to a helicopter when it sets off a mine nearby,” said the retired admiral who fears that the blast and its column of water could down the aircraft. “We’ll just have to wait and see how they do in the gulf.”

While Pentagon strategists confront the immediate challenge in the gulf, three new U.S. mine-hunting and -sweeping programs are under way. All have had their problems.

First is a $1.5-billion plan to build 14 ocean-going, sonar-equipped mine countermeasure (MCM) ships. Two years late, the first vessel is undergoing sea trials in the Great Lakes and will be commissioned next month. Congress has held up funds for three additional ships, however, because of several problems, including difficulties encountered in molding fiberglass over the vessels’ wooden hulls.

Second is a roughly $1-billion effort to build 14 smaller mine hunter-coastal (MHC) ships, which have scaled-down capabilities. Design and construction problems have brought major changes in the program and a contract for the first vessel was not let until three months ago, several years behind schedule.

Third is a program to upgrade and expand the helicopter fleet of 23 Sea Stallions with an improved model that will have three engines instead of two, so that the craft can carry more equipment and stay on station longer. Recent accidents with the current model have led to a review of plans in the $500-million program.