They were trapped 1,575 feet below the Atlantic for 76 hours. Then came a rescue with only 12 minutes of air left

For more than three days, two men sat inside a tiny submersible on the floor of the Atlantic Ocean, more than 1,500 feet below the surface. Their vessel, Pisces III, had been sent down for what was supposed to be routine work laying transatlantic telephone cable. Instead, an accident left the two-man crew stranded on the seabed off the coast of Ireland, with their oxygen supply slowly running out. Roger Mallinson and Roger Chapman knew that every hour mattered.

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When rescuers finally brought them back to the surface on September 1, 1973, the men had spent about 76 hours trapped at a depth of 1,575 feet (480 metres). Only around 12 minutes of air remained. The operation is still recognised by Guinness World Records as the deepest successful underwater rescue.

A routine cable-laying mission goes wrong

On August 29, 1973, Pisces III was operating about 150 miles southeast of Cork, Ireland, as part of work on a transatlantic communications cable. Mallinson and Chapman were experienced underwater professionals. Nothing about the mission suggested that they were about to become part of one of the most remarkable survival stories in deep-sea history. Then disaster struck.

A problem caused water to flood part of the submersible. The small craft lost buoyancy and began sinking rapidly. It eventually hit the seabed at a depth of about 1,575 feet.

The two men survived the impact, but their situation was now extremely dangerous.

They were hundreds of metres below the surface, inside a cramped vessel that could not simply rise back up.

They had roughly 72 hours of life support

The biggest threat was not only the enormous pressure outside the vessel. It was time. When Pisces III reached the seabed, Mallinson and Chapman had an estimated 72 hours of oxygen available. They had no idea whether rescuers would be able to locate them, let alone bring them back to the surface before the supply ran out.

Fortunately, communication with the surface remained possible. That gave rescuers something crucial: the men were alive, and they could coordinate an attempt to save them. But finding a small submersible sitting on the ocean floor was only the beginning.

An international rescue effort begins

News of the accident triggered a major rescue operation involving Britain, Canada and the United States. Other Pisces submersibles were brought into the effort. The U.S. Navy also sent CURV-III, a remotely controlled underwater recovery vehicle capable of operating at extreme depths. The equipment had to travel thousands of miles to reach the rescue site.

The conditions were difficult from the start. Heavy seas complicated operations on the surface, while equipment problems threatened to slow the effort below it. Yet rescuers continued working because there was no luxury of waiting.

Inside Pisces III, Mallinson and Chapman conserved their oxygen by keeping movement and activity to a minimum. Their careful use of the limited life-support supply eventually gave the rescue team additional time.

The first attempts were not enough

Getting a rescue line attached to Pisces III at that depth proved extremely difficult. The rescue team eventually succeeded in connecting equipment to the stranded submersible, but the operation did not go smoothly. CURV-III itself became entangled during the lifting process, forcing rescuers to abandon it and change their approach.

The goal remained the same: somehow bring the tiny submarine and its two occupants upward without losing the connection. The rescue vessel John Cabot ultimately played a central role in the operation, while other underwater vehicles and divers assisted at different stages.

Slowly, Pisces III began its journey home

Once a secure connection was established, Pisces III was gradually pulled toward the surface. It was a painfully slow process.

The submarine had to be raised through hundreds of metres of water while rescuers dealt with cables, equipment and the dangers created by the rough conditions. At shallower depths, divers were finally able to assist with the lifting operation.

For Mallinson and Chapman, however, the danger was not over. They had already been trapped for more than three days. And their air was almost gone.

Just 12 minutes of air remained

On September 1, Pisces III finally reached the surface. The rescue had succeeded. But the margin was astonishingly small. Reports later established that only about 12 minutes of oxygen remained when the submarine was brought back to the surface. The men had survived roughly 76 hours in the depths by conserving their limited life support and relying on the rescuers above.

They had gone down as part of an ordinary working mission. They came back as survivors of what Guinness World Records recognises as the deepest underwater rescue ever successfully completed.

A rescue that changed underwater survival

The Pisces III rescue became more than an extraordinary story of survival. It also demonstrated how difficult deep-sea rescue could be and how much specialised technology and international cooperation mattered.

Roger Chapman later dedicated much of his career to submarine rescue and underwater safety. The experience helped shape his work in developing rescue technology for people trapped beneath the sea.

More than five decades later, the numbers alone are difficult to comprehend: 1,575 feet underwater, 76 hours trapped and just 12 minutes of air remaining. Two men went to the bottom of the Atlantic expecting to complete a routine job. Against extraordinary odds, both came back alive.