The Seals, the James Bonds of the Navy, have updated David Bushnell's one-man underwater boat of the Revolutionary War and built 15 minisubmarines for sneaking in and out of unfriendly places, the new commander of the nation's special forces disclosed yesterday.

Gen. James J. Lindsay, commander of the new U.S. Special Operations Command, told defense reporters at a breakfast meeting that the Seals have two- and six-man versions of the minisub. The tiny craft can quietly approach enemy ships or beaches at a speed up to six knots, or 7 mph, he said.

Other sources said the two-man sub is known as the "wet" version because it remains full of water while operating, requiring its crew to wear scuba diving wet suits and air tanks. The six-man model is dry inside like a standard submarine. Both versions are propelled by batteries.

The midget subs are carried in compartments atop large, nuclear-powered subs. Near the destination, the crew climbs from the submerged mother ship into the minisub through an airlock, open the outside compartment doors and noiselessly move off in the small vessel.

On a typical reconnaissance mission, the two-man sub would surface, allowing the crew to open roof hatches and look around unencumbered by a scuba mask, sources said. The wet sub could be left submerged, with location marked by a buoy, while its crew goes ashore.

There have been reports in recent years of landings on the Swedish coast by Soviet survey teams using minisubs and other small submersibles.

One of the Navy Seals' mother subs is the nuclear-powered USS John Marshall, which, like several other boats, has been retired as a ballistic-missile vessel, but modified by the Navy so that Seals can swim out the missile hatches while the ship is submerged. Seal stands for sea-air-land.

Lindsay said the minisubs, called SDVs for Swimmer Delivery Vehicles, can plant a magnetic bomb on the bottom of an unsuspecting ship in a harbor or sneak Seals, Green Berets or other commandos onto hostile beaches for counterterrorist missions.

Lindsay's portrait sounds much like what Bushnell designed his "Turtle" to do. The wooden, egg-shaped "Turtle" -- 7 feet deep and 5 1/2 feet wide -- called for one busy man to hand-crank a propeller, navigate his almost-submerged craft across a harbor and, when reaching a British ship, twist a large screw into the wooden hull of the ship, attach a 150-pound package of gunpowder and move off underwater before the timer detonated the explosive.

Such an attempt was made on the British warship Eagle off Staten Island in September 1776, but the Turtle's hapless crewman, Sgt. Ezra Lee of the Continental Army, could not penetrate the Eagle's copper sheathing with the screw, and had to abandon the attack. The Turtle apparently was lost about a month later when its mother ship sank in the Hudson River, Navy historians say.

The Japanese deployed two-man midget subs to Pearl Harbor before their bombers struck on Dec. 7, 1941. They carried two torpedoes but inflicted no major damage, according to historians.

Despite such an uncertain record, Lindsay said the Seals' minisubs are "a hell of a lot better than Boston Whalers" used in limited military operations such as the 1983 Grenada invasion. He said the SDVs' potential for counterterrorism is obvious: "Infiltration and exfiltration {taking men in and out of hostile areas covertly} is one of the biggest challenges we face."

But the minisubs, submarine specialists say, have several disadvantages: limited range, slow speed and lack of defense, relying primarily on stealth and quietness to survive. The Navy is assessing European minisubs to improve capabilities for covert operations around the world, sources said.

The Rube Goldberg-like submarine shown above in cross-section, was the brainchild of David Bushnell, a Yale College student known for his early experiments with underwater explosives.

In 1775 Bushnell designed and built the hand-cranked "Turtle," equipping it with a tank that could be filled to submerge the craft, then pumped out for surfacing.

The Turtle was used-without success-against the British during the American Revolution.