Beyond these relatively minor burdens, living and working on the seabed posed a host of dangers. Chief among these was the threat of decompression sickness, which occurs when divers surface too quickly to adjust to the change in atmospheric pressure. After a few hours spent at a depth of more than 30 or so feet, blood and body tissues become saturated with nitrogen. If the aquanaut returns to the surface without adequate decompression - which takes 24 hours per 100 feet to complete - the nitrogen escapes and forms bubbles in the bloodstream. These bubbles - coursing through the body like the bubbles in a can of soda - cause the dreaded malady known as "the bends."

The bends are every diver's worst nightmare, an ailment whose symptoms are almost absurdly multiform: blurred vision, loss of speech and hearing, pain in the joints, confusion and erratic behavior, incontinence, breathing difficulties, itching, swelling of skin, seizures, paralysis, excruciating pain, unconsciousness, and death. As long as they remained in their habitats, aquanauts were able to go out on dives without risking decompression sickness because their environments were kept at the same pressure as the surrounding ocean. But the danger eventually had to be faced.

On top of all this, there was the sheer creepiness of finding oneself stranded in such a hostile, remote environment. Ian Koblick, widely regarded one of the world's foremost authorities on undersea habitats and co-author of Living and Working in the Sea, described the sensations of that first night on the sea floor:

You're on the bottom without a speedy escape hatch. This is, in some respects, the moment of truth. You're now linked to the habitat and your fellow aquanauts in a life-dependent symbiosis. You ask yourself if all the systems will work. What are all those strange noises? Will I get lost and be able to return to the habitat?

But Koblick also recognized a flip side:

There is a surprisingly rapid change from being an alien visitor in another world to becoming an integral part of it.... Gazing out the ports, especially at night, is a unique experience; to swim out of a home in the sea by moonlight and watch ethereal shapes passing all around is unforgettable.

Indeed, many aquanauts had near-ecstatic experiences. A French aquanaut, in typical French fashion, described his encounter with the deep this way: "I am the same person, yet I am no longer the same. Under the sea, everything is moral." The great majority of aquanauts, though, were driven by flat-out scientific curiosity, an understanding that the oceans - because of the supplies of food and natural resources they provide, as well as their effect on climate - would play a vital role in our continued existence on the planet. And so by the late '60s, undersea-habitat missions proliferated like mad.

The most ambitious of all was Sealab, a US Navy-funded project that reached its zenith with Sealab III, a 1969 mission that called for a crew of aquanauts to spend two weeks under 600 feet of water off the California coast. It was a dizzying proposition at the time, similar in scope to putting a man on the moon. As one aquanaut puts it now, "If we had been successful with Sealab, it would have opened the door for underwater habitats." But Sealab was not successful. In fact, by the time that mission was over, the door had slammed shut on undersea living once and for all.

Sealab III ended in tragedy when Barry Cannon, a civilian diver and technician, donned his wet suit and scuba gear to find the source of a leak discovered early in the mission. His breathing equipment failed and he suffocated. Sealab III was abandoned. Shortly afterward, the Navy withdrew funding for manned undersea exploration altogether.

Although conventional wisdom holds that Barry Cannon's death killed undersea habitation, Richard Cooper, one of the Sealab III aquanauts, believes the accident may merely have provided a convenient excuse. "Sealab was designed to train Navy divers," he says. "I, as a naive marine biologist, thought the mission was for research, but that whole program was designed to train divers to do covert work off the Kamchatka peninsula off Russia, to tap into wire communications from missile sites, to listen in on the most secret of secrets. When the Navy brass decided to close the program down, they had already trained the people they needed to train."

In any case, the ever-increasing cost of supporting human life undersea, and the growing availability of unmanned exploration vehicles, soon caused others to abandon their undersea-living programs. Before long, the habitats that had caused so much excitement lay rusting in Navy and scrap yards, or were simply left where they stood, home only to the fish and the squid. As space exploration reached new heights, undersea exploration took a nose dive. Even Jacques Cousteau, in his later years, expressed doubt about the idea of undersea living: "It's cold, it's dark, and it's wet." And that, as far as many were concerned, was rock bottom.

TODAY, MORE than 30 years later, only two undersea habitats exist, and only one of those is devoted to research (the Aquarius lab, located in southern Florida). The decline has been, for those who dedicated their lives to undersea living, a terrible blow. But there are those for whom the dream is still very much alive. Cooper, now 65, is director of the Connecticut-based Ocean Technology Foundation (OTF), which is trying to fund and build an undersea habitat, possibly within the next 10 years. "I miss it a great deal," Cooper says of his work on Sealab. "It was by far the most exciting phase of my life. I'd do it again in an instant if I could. If I can play a key role and make the next [habitat] happen, I'll be one of the first ones down there."

As for Koblick, a veteran aquanaut who today runs the Florida-based Marine Resources Development Foundation, he's a little less sanguine. "There has been no concerted effort and no money put into this," he says. "I've spent 30 years appealing to governors and presidents and other politicians - as soon as you get them convinced, they're either assassinated or kicked out of office or not re-elected. All those promises and nothing happens."

But Koblick has found a way around the lack of government dollars - and in so doing he may just have devised a way to resurrect the idea of undersea habitats.

In the mid '80s, Koblick and another aquanaut acquired an old habitat and converted it into an aquatic hotel. Located in 30 feet of water just off Key Largo, Jules' Undersea Lodge contains two bedrooms (equipped with all mod cons), a common room, a kitchen, and a dining area. Like the underwater habitats of old, Koblick's lodge is a little cramped and a little damp, but even at a cost of $350 per person per night, the rooms are booked months in advance.

And Koblick's modest hotel is only the beginning. As military and research cash dries up, it seems a fair bet that many of the underwater habitats of the future will be built and paid for by deep pockets in the leisure industry. "The ocean's becoming a playground," says Cooper. "This country spends many billions of dollars a year in marine-oriented recreation. It's just a matter of time before entrepreneurs set up underwater hotels." After all, if Dennis Tito was willing to part with $20 million to spend a few days on the International Space Station, there will surely be plenty of well-heeled pioneers eager to shell out a few thousand bucks for the opportunity to sleep with the fishes.

Indeed, several companies are involved in hurried and secretive campaigns to build the world's first undersea resort. Right now, it looks as if the prize will go to a Florida outfit called US Subs, which already does a roaring trade renting submersibles. According to the company's co-owner, Bruce Jones, US Subs has two major projects in the works - "very serious, well-funded efforts": a 20-room hotel complex with a 60-seat restaurant and a 60-seat bar, and a much larger, 300-room complex. He hopes to start construction on the smaller hotel within six months. "We are looking at several locations," he says, "including the Caribbean and the South Pacific."

These hotels will bear little resemblance to the clanky, crypt-like, cigar-shaped habitats of yore. They will be located at much shallower depths; access will be by elevator or escalator; the atmosphere will be kept at surface-level pressure; and, perhaps most important, they will be dry. In many ways, these resorts will resemble large, fully submerged aquariums.

"With our hotel," says Jones, "about 70 percent of the surface area will be transparent acrylic. The walls and ceilings will be essentially transparent." He adds: "We've spent a lot of time doing calculations and figuring out how to optimize visibility without compromising structural integrity."

Underwater luxury may sound light-years away from Winslow Burleson's overly buoyant underwater tent, but in many ways Burleson is pursuing the same dream as Koblick, Jones, and the host of leisure-industry companies racing to put pillows with mints on them at the bottom of the sea. "You could put some form of cot in it," he says of his tent. "You can do a fresh-water rinse, get a bit comfortable, have a bit of a meal. You could have a battery heater."

Burleson hasn't even begun to think in terms of marketing just yet, but he has mentioned his idea to a few friends. "I have a fun time describing it," he says. "A lot of people get really excited; they want to know when it's going to be ready. But there are plenty of people who ..." He pauses. "There are people who just don't want to go underwater."

Chris Wright can be reached at cwright[a]phx.com.