In the 1960s, as America raced to the Moon, the Navy sent aquanauts to the ocean floor off La Jolla in an ambitious experiment called SEALAB II.
Lately, with Artemis II swinging around the far side of the Moon and sending back stunning footage of an earthrise, space is kind of exciting again. Seeing Earth from that perspective reminds us what big, ambitious projects can do…recent NASA defunding notwithstanding (what a disaster).
But!
As I’ve written here before: while we look up, it’s also worth remembering to look down.
In the early days of the space race, that was the mindset as well. As the Gemini program was getting underway, building on the earlier Mercury program missions (“Godspeed, John Glenn”), there was a parallel effort to go the other way. Not into orbit, but deep down…into the ocean. The aspirations were similar: If humans could learn to live in space, maybe they could learn to live on the seafloor too.
For a brief window, we were serious about both. And there were even a few individuals who were part of the two programs: astronaut/aquanaut Scott Carpenter was one of them.
Unfortunately, while we managed to go to the moon on Apollo (and hopefully soon again with Artemis), the ocean effort stalled and never really came back. That story is largely forgotten now, but it’s interesting, and it has a very specific California angle. In fact, one of the most ambitious attempts to allow humans to live on the ocean floor took place just off San Diego, coincidentally, near the same stretch of sea where the Artemis astronauts recently splashed down to Earth decades later.
The project was called SEALAB II. Let’s get into it.
There were many reasons to try to live beneath the waves. The scientific potential was enormous, but so were the military applications. Aquanauts, as they were called, could work for hours at depth, something that was nearly impossible before.
There was a distinct national vibe for this kind of thing.
In 1963, John F. Kennedy told the National Academy of Sciences, “To a surprising extent, the sea has remained a mystery. We know less about the oceans at our feet than the sky above our heads.” He pushed Congress to invest in ocean research, warning that “knowledge of the oceans is more than a matter of curiosity. Our very survival may hinge upon it.” That remains true.
Living underwater may not seem as extreme as space, but it comes with its own set of problems. Breathing is the obvious one. We can’t inhale water. Then there’s pressure, which increases rapidly with depth and changes how the body functions. It has a tendency to crush things. Even shallow diving can cause problems. As a certified scuba diver, I’ve had several scary moments underwater in my lifetime. Further, deep water is cold, and water has a much higher thermal conductivity than air, so you lose heat much faster. Visibility is limited. And yes, there are living things down there that can kill you.
In other words, if humans were going to live underwater, there was a lot to figure out.
The effort started in 1964 with SEALAB I, launched by the U.S. Navy. Engineers built a pressurized habitat that could support a small crew for days at a time. In that first mission, four men lived for 9 days at a depth of about 192 feet off Bermuda. It proved the basic idea could work. Living at depth for days at a time changed what divers could see. Instead of brief visits, they became part of the environment. Marine life carried on around them. “You could see these animals doing things undisturbed. They sort of got used to us,” aquanaut Richard Grigg said after emerging from SEALAB I.
SEALAB I did some science, but it was mostly a proof-of-concept. It was time to ramp things up.
There’s kind of a crazy hero in all this who deserves mention, although I won’t go into too much detail about him because it would take pages, but he’s one of the more unusual figures in the history of ocean exploration. If you want the full story, Ben Hellwarth’s book Sealab: America’s Forgotten Quest to Live and Work on the Ocean Floor is excellent. I read it a few years ago, and a lot of what’s here comes from notes I took then.
That man was George Bond. Yes, Bond. George Bond.
Bond was a Navy doctor, but also a researcher, a diver, and one of the few people willing to rethink the fundamentals of how humans operate underwater. Bond saw a flaw in traditional diving. Divers spent hours decompressing near the surface for just minutes of work. His solution was saturation diving, which in many ways was still theoretical. But the basic idea is simple: keep divers at depth for days or weeks, then decompress once at the end.
And so, after the success of SEALAB I, the next step was clear. SEALAB II.
Off San Diego, the Navy significantly scaled up what had been accomplished near Bermuda, placing a larger habitat about 205 feet below the surface on a ledge along an undersea canyon in the murky waters off La Jolla. The uneven seabed left the structure slightly tilted, enough that loose objects would slide across the floor, prompting one aquanaut to nickname it the “Tilton’ Hilton.” But compared to the cramped design of SEALAB I, the new habitat felt almost luxurious, with larger sleeping and eating areas, a dedicated lab, and even a few unexpected flourishes, including an exterior shark cage and curtains on its 11 portholes.
Inside, small teams of aquanauts, usually three at a time, lived under pressure for weeks, breathing a helium-oxygen mix. This was the key to saturation diving, but it had not been thoroughly tested or proven over long periods of time.
As you likely know from high school chemistry class, the air we breathe is around 78 percent nitrogen. Under pressure, nitrogen from the air dissolves into the body’s tissues. Come up too quickly, and that nitrogen forms bubbles, causing severe pain or even death. It’s known as decompression sickness, or, simply, the bends.
Saturation diving reduces that risk by replacing most of the nitrogen with helium, allowing the body’s tissues to fully saturate at depth. Helium still dissolves under pressure, but it doesn’t have the same narcotic effects as nitrogen and moves through the body much more quickly, making it easier to manage during that single decompression.
And so, from August to October 1965, three teams of aquanauts, Navy divers and civilian scientists, each spent about 15 days living 205 feet below the surface off La Jolla. They carried out research on human physiology, ocean science, and underwater operations, even working with a trained porpoise named Tuffy to test the idea of animal-assisted rescue.
Aquanauts also tested tools, ran experiments, and proved that saturation diving was practical. The program also explored underwater construction and the limits of human endurance in isolation.
There were real risks. Gas mix errors, equipment failures, and the constant threat of decompression sickness or oxygen toxicity were always lurking. Even small mistakes could escalate quickly at that depth. The helium-oxygen mix itself created challenges, distorting voices and making communication harder.
There’s a great, hilarious even, recording of Scott Carpenter speaking from the seafloor with President Lyndon B. Johnson. Breathing a helium-oxygen mix, his voice comes through high and distorted, the same way your voice sounds funny when you inhale from a helium balloon, except that it lasted for the duration of the mission.
Here it is:
SEALAB II was, in many respects, a success. It showed that humans could live and work at depth for extended periods, proved the practicality of saturation diving, and led to new insights into human physiology and long-duration isolation. Briefly, it suggested a real future in which people might live and work routinely on the ocean floor.
It also set the stage for SEALAB III in 1969, conducted off San Clemente Island, which aimed to push the concept deeper, to more than 600 feet.
But it was not to be.
Almost immediately, SEALAB III ran into trouble. A leak contaminated the habitat’s breathing system, making it unsafe for a full crew. The Navy quickly sent divers down to investigate and repair the problem, but the risks at that depth were significantly higher than in SEALAB II. The habitat developed issues with its breathing system, and there were concerns about contamination and whether the air supply was safe.
During one of those repair dives, aquanaut Berry L. Cannon was sent down to assess the situation. His gear relied on a chemical scrubber to remove carbon dioxide from the air he was breathing, a precursor to the so-called rebreathers that are common today. At some point during the dive, the system failed, likely due to a problem with the absorbent material used to filter out CO₂. Without scrubbing, carbon dioxide builds up quickly in a closed breathing loop. The result is confusion, loss of consciousness, and death.
Berry Cannon was gone.
The incident exposed just how narrow the margin for error was. At those depths, even a small equipment issue could become fatal in minutes. It also raised broader concerns about the safety of the entire operation, including whether the systems had been adequately tested under real conditions. People had also died in the space program, but for some reason, this was different.
Within weeks, SEALAB III was shut down.
As Carpenter later put it, the ocean never quite captured the public imagination the way space did. “Work in the deep water is just not as glorious a pursuit in the minds of most people as a flight to the moon,” he told CBS in 1968. “It’s a cold, dirty place, and you can’t see very far. You can’t go down and take pictures that thrill the world.”
It’s hard not to ponder what might have followed if SEALAB had continued. The idea of people living on the ocean floor is still pretty captivating. Not just for science, but also for tourism. Living in the ocean changes how you observe it. It slows things down. It lets the environment reveal itself in ways short visits using scuba never can.
There are several encouraging signs that the idea may not be entirely gone. Projects like DEEP’s Vanguard and Sentinel habitats are revisiting the concept, and could point toward a more permanent human presence on the ocean floor.
This project is new to me. I only discovered it while reporting out this article. DEEP is a British company, but they’ve been building out facilities in both the U.K. and the U.S., including a pilot deployment at Tennessee Reef in the Florida Keys National Marine Sanctuary. This is supposed to happen as early as the end of May 2026. So, wow, yeah. Pretty neat.
