In 1965 the President of the United States picked up the phone to congratulate a man who had just spent a month living on the floor of the Pacific Ocean. Lyndon Johnson wanted to praise aquanaut Scott Carpenter, who took the call from a decompression chamber aboard the surface support ship, still breathing a helium-rich mix as his body worked off weeks of dissolved gas. The helium had turned his voice into something like a cartoon rodent, and as the Navy Experimental Diving Unit tells it, the phone operators handling the call could not make him out.

Carpenter was the second American to orbit the Earth. By 1965 he had swapped frontiers and joined SEALAB, the US Navy’s attempt to find out whether people could simply move in downstairs.

The maths that made it look inevitable

SEALAB was the obsession of Navy doctor George Bond, known to his divers as Papa Topside. His problem was decompression. A diver’s tissues soak up breathing gas under pressure, and shedding it safely takes time, so a surface-supplied diver could spend hours coming back up in exchange for minutes of work on the bottom. Bond’s insight, documented by the US Naval Undersea Museum, was that after roughly 24 hours at depth the tissues saturate and the decompression bill stops growing.

Stay a day or stay a month, and you pay once.

Two habitats that worked

SEALAB I went down off Bermuda in 1964. Four divers lived at around 192 feet for about ten days before a hurricane cut the mission short, and the National Museum of the US Navy records that they completed in a week tasks that would otherwise have taken conventional divers a year.

SEALAB II was bigger and nastier, lowered off La Jolla, California in August 1965 to a depth of 205 feet in cold, murky water. Three teams of ten divers each spent 15 days inside, testing tools, raising a sunken fighter jet, setting up a weather station and working with a trained porpoise called Tuffy who ferried gear from the surface. Carpenter stayed for 30 days. By the time the habitat came up, PBS American Experience puts the run of continuous occupation at 45 days.

Navy brass were pleased and reporters were delighted. Underwater colonies started to sound less like Jules Verne and more like a procurement schedule.

February 1969

SEALAB III was the same hull, reworked and rated to 600 feet. On 15 February 1969 it was lowered off San Clemente Island, California, to about 610 feet, and it started leaking helium almost straight away. Four divers went down twice in a transfer capsule to plug it.

On 17 February, Berry Cannon, a 33-year-old civilian electronics engineer who had served on SEALAB II, began convulsing on the sea floor. His team dragged him back into the capsule. He was dead before it reached the surface. A Navy board of inquiry concluded he had died of carbon dioxide asphyxiation. The baralyme canister in his rig, the part meant to scrub what he exhaled, was empty.

That finding has never been fully accepted. Writing in InDEPTH, engineer Kevin Hardy sets out the divers’ own account, including the argument that electrocution fits the evidence better than carbon dioxide. He quotes team engineer Lieutenant Commander James Osborn, who reckoned the cold alone would have killed men had the habitat ever been opened.

That is participant testimony, not a revised verdict.

Why no one built the sequel

SEALAB stopped that morning and never restarted. As Live Science reported, Cannon’s death ended not just SEALAB III but the Navy’s saturation diving experiments altogether, and the whole program was wound up by 1970.

Saturation diving itself did fine. It went commercial and offshore, where the money was. Divers now live in pressurised chambers on the deck of a support vessel and commute to work in a diving bell, which delivers everything Bond promised without the house on the sea bed. Then robots took over the deepest jobs. A 2025 breakdown from CLIMB puts standard saturation diving depths at up to 300 metres, with the deepest dive on record reaching 328 metres. A work-class remotely operated vehicle, meanwhile, is commonly rated to several thousand metres, and Dockstr‘s current buyer’s guide notes that some specialised units reach 6,000 metres.

What survived

One habitat is still down there. Aquarius Reef Base, run by Florida International University at 60 feet off Key Largo, is the world’s only underwater research laboratory, and NASA has borrowed it for years to rehearse spacewalks, since buoyancy does a passable impression of low gravity.

The rest is museum stock. A steel end bell off the SEALAB II and III hull sits on display at the museum in Keyport, Washington. The Experimental Diving Unit says the dish was formed in four thousandths of a second by detonating a hundred pounds of plastic explosive under San Francisco Bay. At the time that counted as a sensible way to build a house.

The underwater future was quietly subcontracted, and the habitat turned out to be the one part nobody needed.