In 2026, a crew of six fully-trained aquanauts will be deployed to a new oceanic habitat system – beginning what promises to be the era of humanity’s continuous presence underwater.

A cable vanishes from the surface, stretching away into the abyss. The water is crystal clear, yet just 20m (66ft) down – even with its lights on – the remote operated vehicle (ROV) attached to that cable is beyond the reach of our vision. What must it be like looking up from that depth? What about 10 times that depth? Most humans who venture down that far can only get a brief glimpse of what life is like at those depths. But what if you were able to stay down there for days? That is exactly what the experts at Deep aim to do.

Manufacturing of the ocean technology and exploration company’s “subsea habitats” has already begun and, on 3 November 2026, they plan to deploy a crew of six fully trained “aquans” to their newly unveiled Sentinel oceanic habitat system. Deep hopes this will begin an era of humanity’s continuous presence underwater, an ambition that will mirror the achievements already made in outer space. The technology will allow people to live at depths of up to 200m (656 ft) for up to 28 days at a time – revolutionising the way scientists observe, monitor and understand the oceans.

On the edge of the Forest of Dean in Gloucestershire, south west England, Dayhouse Quarry sits between the tree-line and the flood plains that sweep down towards the River Severn. Enclosed by 70m-tall (230ft) sheer cliffs, there is no wind. In this secret enclave, a bright blue pool sinks to depths of 80m (260ft). It’s here that I’m standing on a pontoon, as the Deep team carry out a practice rescue procedure. We watch the ROV from a screen as its manipulator connects a hook to a mock submersible, to winch it to the surface.

Rob Colley, ex-military elite diver and yoga teacher, now heads up the company’s training and human performance division. One element of Colley’s work is “breath hold training”.

“Carry out your breathe up practice, take a deep breath, then hold it,” he says. “You’ve got rid of all your excess CO2, which in turn stimulates the need to breathe. However, you’ve got lots of oxygen in your body, so you shouldn’t really need to breathe for up to six or seven minutes.” Through specific breath training, he says, we can reprogramme our psychophysiological processes, allowing us to regulate our own nervous systems. (Extreme care should be taken when practicing these techniques as if done incorrectly it can lead to serious risks.)

“When you submerge into water, your body naturally has this dive reflex,” says Colley. “It shuts down the peripheral circulatory system for efficiency, bringing the oxygenated blood to your central system – and allowing you to hold your breath a little bit longer.” The diving response is a reaction that occurs in all mammals – including humans – when they are submerged in water, and it limits unnecessary oxygen consumption. “So, we do have this adaptability to being in the water.”

There is evidence that humans can become more “aquatic”. Take the sea nomads of Indonesia who have developed genetically enlarged spleens, which enable them to free dive to depths of up to 70m (230ft) for as long as 13 minutes at a time. Humans have an innate drive to overcome our natural limits – to fly like a bird, to reach outer space. Now, with the help of Deep, could humans learn to live in the depths of the ocean?

The idea of humans living underwater is not new. In the 1960s, the French ocean explorer Jaques-Yves Cousteau built an underwater village. Other projects followed – but none have so far resulted in a continuous human presence under the sea.

Tammy Horton is an expert in deep-sea biodiversity at the National Oceanography Centre (NOC). She researches the impact of climate change on deep sea creatures, specifically crustaceans. “Of which there are many, many, many – lots of them new to science,” she says. “The oceans are the largest environment on Earth. It’s important to understand what changes are happening there – as it impacts everything on our planet, everyone’s lives.“

At the surface, the epipelagic – or “sunlight zone” – is warmed by sunshine. Its temperature varies – from 28°F (-2°C) near the North Pole to 97°F (36°C) in the Persian Gulf – across seasons and latitudes, constantly stirred by the wind. At depths of 200m (656ft) water temperature decreases rapidly. In the dim light of the twilight zone, fish with large upward facing eyes watch for silhouettes above, while bioluminescent creatures glow like apparitions.

“As you go deeper, the light is absorbed by the water. This happens colour by colour,” says Phil Short, one of the world’s foremost technical divers. Short has logged over 7,000 hours underwater, over a 33-year-long career. At Deep, Short leads all areas of research diving, test diving and dive training.

“The reds disappear first,” he says. “If you’re diving at a depth of 20m (66 ft) and you get a small cut on your finger, say from touching a rock, the blood comes out like a black smoke. Descend further and it’s green smoke. As you go deeper, you go all the through all the colours of the spectrum. Eventually, in the really deep ocean, you’re left with only dark blues, indigos, violets.”

This is at around 200m (656ft) down. This, the very edge of the twilight zone, says Short, is too deep for most divers, but too shallow to justify the cost of commercial deep-water equipment. “So, it’s a band of water that is very understudied,” he says, “and the potential for things to be found there is enormous.”

Being able to descend to 200m (656 ft) would allow access to the entirety of the epipelagic zone, the deepest point at which sunlight penetrates into the ocean – and where it’s estimated that 90% of marine life is found.

“Throughout my career I’ve gradually progressed into deeper and deeper water, both in the ocean, and in caves and mines,” says Short, “to see things no human being has ever seen before, places no light has ever shone.”

Dark, vast and seemingly unreachable, the ocean floor is crucial to our lives through the services that it provides, such as the sequestration of carbon. Deep ocean phytoplankton forms the basis of food chains which sustain billions of people. Meanwhile hydrothermal vents and other deep-sea environments host life forms like bacteria and sponges that could provide a source of new antibiotics and anti-cancer drugs.

“At NOC we tend to send robots or sensors down,” says Allison Schaap, a research engineer and associate head of NOC’s Ocean Technology and Engineering Group. “Then we use people to understand the data and to make decisions about it.”

Schaap says it’s more efficient to send technology than humans to collect samples from the deep ocean. “You can appreciate the beauty of a river or a stream, you can feel a connection to it – but you can’t look at it and say, ‘What’s the pH?’ or ‘What’s the amount of nitrate in it?’ So from an engineering point of view, we focus on getting the data rather than sending people. Certainly, it’s a lot safer.”

There are robotic explorers beneath the waves at this very moment, allowing ocean research to be carried out without the need for a human presence. Horton works from a land-based lab with specimens collected using corers and traps guided by ROVs but, she says, most of the specimens she examines are dead on arrival.

“You can gain a hell of a lot of information from a specimen – in fact more than you can probably imagine – but you look at them and think, ‘I don’t have an understanding of what this animal is doing in life, how they’re interacting, how they’re feeding, how they’re behaving’. I think anyone who works in deep ocean research wants to be able to access the environment and to see it firsthand, to actually see the animals in their natural environment.”

This is where human-occupied vehicles (HOVs) come in. HOVs are renowned for their contribution to research breakthroughs, including the discovery of hydrothermal vents and the investigation of the RMS Titanic shipwreck.

However, the sea floor is an ever-changing landscape, says Colley, which poses a challenge when you have limited amount of time to research. “With conventional diving, you go down for a certain amount of time, then you have to decompress on the way back up. This means the time actually gathering samples or doing your work is limited to something like 16 minutes at around 100m (328ft) depth.”

When researchers return to the seabed, he says, the tide will often have moved the sand and the work will need to be repeated.

“What [the Sentinels] will allow us to do, is stay for a prolonged period,” he says. “It’s a more efficient way to operate. Also, if you place them down at 200m, you can use them as a forward operating base.”

However, high pressure, low temperatures and corrosion all pose serious challenges to equipment in the deep ocean. To cope in what is often considered among the most extreme environments on the planet, Deep’s Sentinels will be made from the same materials used to make space rockets. Louise Slade, Deep’s director of advanced manufacturing says: “We’ll be 3D printing with steel and cladding the Sentinels in Inconel”.

Inconel, she explains, is a nickel-chromium-based superalloy widely used in the military and aerospace industries – in extreme environments where components are subjected to high temperature, pressure or mechanical loads.

Deep’s system of configurable, customisable and flexible subsea habitats will be self-sufficient, powered by renewable energy, with subsea bio-reactors to sustainably deal with waste, and be independent of the surface. The subsea habitats will allow scientists to live at depth for weeks rather than minutes. They will have access to the water through a moon pool (essentially a hole in the floor that leads out into the ocean), as well as dedicated wet and dry labs.

However, much like spaceflight, life aboard a submarine is widely recognised as one of the most stressful and psychologically demanding experiences. Subsea habitats are often cramped, and inhabitants have to deal with confinement, absence of day/night cues, lack of privacy, and isolation from the outside world.

“We’ll be studying whether people can cope with being isolated in a remote place that you just simply cannot leave,” says Short. This research lends itself to space travel too, he says. “If we’re going to send people to Mars, that will be a three-year mission. It’s important to understand how six people would cope with being trapped in a tin together for three years.”

The Sentinel is 400m3 (14,126 ft3) in length and 6.2m (20 ft) in diameter – roughly half the size of a Boeing 777’s fuselage. It can house six people at a time and says it will offer comfort “unlike any other subsea habitat“. Habitants can enjoy a good night’s sleep in a private bedroom, proper food prepared in a kitchen, and a warm comfortable living environment.

So, are we about to return to the oceans we crawled out of some 375 million years ago? Much like the moment in 2000, when humans established a permanent presence in space, Deep aims to create an “International Space Station for the oceans”. Perhaps reforming our connection with this vast unknown landscape will help us realise its importance for the future of our species, and for the Earth itself.

“Who knows,” says Colley, “maybe in 300 years’ time we’ll look back and think, ‘This is where it all began’.”

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