AS ONE walked into the U. S. Navy's Minesweep Officer's School in Charleston, S. C. in the early 1960s, you couldn't miss a very large photograph hanging on the wall. It showed the stern of a ship, a minesweeper, swallowed in a huge, boiling ball of water that rose high above the ship. At the top of the plume was the tiny figure of a man.

"That," all of us young, eager, about-to-be minesweep officers were told, "was a minesweep officer who didn't pay attention to what you are supposed to learn here."

Over the next several weeks, the sum of our knowledge was expanded to include the geometry and mechanics of sweeping mines and rendering them harmless. Along with that came the dawning realization that the art of mine warfare was well ahead of the art of mine countermeasures.

Reports coming out of the Persian Gulf indicate that that still may be true. The mine explosion that damaged the reflagged tanker Bridgeton and threw a monkey wrench into the Navy convoy system is strong testimony to the deterrent muscle of mines, the danger of constant and shifting unknowns, the invisible threat sown in stealth.

The mines that have stopped the American reflagging and convoy effort in the Persian Gulf are reported to be ancient, pre-World War II models. Moored mines, anchored to the bottom, lurking just below the surface of the water, which explode on contact with a ship's hull. These mines are the equivalent of ambush by the nerds.

There are much more sophisticated types available. These are the kind of mines that lie on the bottom, waiting. And, in some instances, counting. They come in several different varieties, in that they can be set off by the sounds a ship -- particularly its propellers -- make, by the magnetic signature of the ship, or by the inescapable pressure wave a ship creates as it moves through the water. They complicate the task of neutralization.

The sleek steel warriors of the Navy, the greyhounds, are not equipped to do this job. That created an ironic situation in which the damaged tanker, the Bridgeton, turned out in the end to lead the convoy of warships, because the Bridgeton, with its bulk and compartmentalization, could take another mine hit better than any of the warships. So the greyhounds must give way to the mongrels, the minesweepers.

We are talking here the difference between brain surgeons and plumbers. Minesweepers are slow, plodding, wooden, ugly. In the 1960s, they abounded at the Navy base in Charleston, threading the currents of the Ashley-Cooper River, chugging out to the Altantic and watching the gallant destroyers flash by.

Once out in the Atlantic, we commenced to practice, to stream gear. Sweepers were equipped with various devices to equalize mines, the simplest of which was supposed to be the sweep wire for moored mines. Simply put, the end of the wire was attached to a large metal device that looked like a venetian blind, and the water moving through the slats of the blind moved it out and away from the ship.

When deployed, the sweep wire, which could be adjusted for various depths, swung out from the stern of the ship in a J-shape. We used two wires, one from each side of the stern. Metal serrated jaws, called cutters, were set at designated intervals along the wire. The theory here is that the wire anchoring the moored mine would be picked up by the sweep wire and severed by the serrated jaws of the cutter. The mine would pop to the surface and be dispatched by fire from the 40-milimeter gun on the bow, the sole armament of the ocean-going minesweeper.

We also spent some time sweeping practice bottom mines. To sweep an acoustical mine, one that is detonated by the noise of the ship, we lowered a device over the side that was in effect a giant hammer. Turned on, it made an awesome racket. Water is a very good transmitter of sound, so the theory was that the sound from the hammer would beat the sound of the ship's propellers to the mine, exploding it harmlessly in front of the ship. "Bet on it," they said in minesweep school.

Magnetic mines explode when they read the magnetic field created by a steel ship. That's why minesweepers are wooden. But they need to sweep magnetic mines for the steel ships that will follow, and to do so they streamed something out the stern of the ship called the magnetic tail. This is a giant-sized extension cord, through which a considerable amount of electricity is pulsed. It floats. The pulsing electricity creates its own magnetic field, which touches off the mine. Does the magnetic field reach far enough in front of and to the sides of the minesweeper so as to make it safe when the mine goes off? "We think so," they said in minesweep school.

That leaves the pressure mine. Any ship that creates a bow wave when it moves through the water (I can't think of one that doesn't), creates a pressure wave. That difference in pressure trips the firing circuit of the mine, and up we go. "Don't go over any pressure mines," they said in minesweep school.

So here's where we came out -- don't hit any moored mines with the ship, assume the acoustical device spreads sound far enough ahead of the ship to detonate mines without harm, hope that the magnetic tail isn't damaged and that the pulsing electricity creates the proper magnetic field, and don't go over any pressure mines.

Here is the kicker -- the mines can count. They can be set for random numbers, say 17. That means that 16 ships -- including sweepers -- can go over them and the firing circuit counts instead of fires. On the 17th ship, it fires.

When we practiced, bottom mines "popped smoke" when they were successfully swept. It was a matter of some conversation on board when the smoke plumes bubbled up 50 feet or so away from the ship.

It is possible that many of the minesweeping techniques and devices have changed over the years, but the trillion-dollar defense buildup seems to have left it in a backwater so far and the three available active duty minesweepers look much the same as they did in the 1960s. Minesweeping by helicopter is a new technique, but they are limited by time in the air as to the area they can cover. And if there have been significant advances in minesweeping and countermeasures, it is equally possible that similar advances could have occurred in the sophistication of mines. I keep thinking of the picture, of the tiny figure riding the explosive plume of water high above the broken stern of the ship.

Tom Wilkinson, an assistant managing editor of The Washington Post, was operations officer aboard the USS Ability (MSO 519) from 1959 to 1961