How could the five passengers on the missing Titanic submarine be rescued?

Experts reveal common recovery methods, though vessel may be too deep

The Cyclops 1 submersible operated by OceanGates. A vessel of the same kind went missing during a dive to the wreck of the RMS Titanic in the Atlantic. David L Ryan / The Boston Globe

Crews aboard the OceanGate Expeditions' submersibles can stay below the surface for days, provided they have enough oxygen. Photo: OceanGate

The bow of the RMS Titanic pictured 4,000 metres beneath the surface of the Atlantic. AFP / Woods Hole Oceanographic Institution

Explorer Hamish Harding, who has lived in Dubai for 30 years, is one of several crew on board the missing submersible. Photo: Instagram

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Finding the submarine that lost communication during a trip to the Titanic shipwreck on Sunday is the biggest challenge facing rescue teams, experts have said.

The American and Canadian navies, government agencies and private companies with expertise in deep-sea operations are attempting to find the submersible, called Titan, and save the five on board.

The area around the Titanic includes large "debris fields" covering several square kilometres made up of objects fallen from the wreck. With countless other items in the area, detecting the missing submersible becomes particularly hard.

"Is there something you can compare to – a scan, a map?" said Ralf Bachmayer, professor for marine environmental technology and deep-sea engineering at the University of Bremen, Germany.

"Can you compare it to something that’s changed? That could indicate a new identified object that may be the submersible. Is that data available to compare to existing maps?"

A power failure could explain why contact with the craft has been lost, while entanglement is another possibility.

The most optimistic scenario is that after a power or communications failure, the vessel has risen to the surface somewhere, with the search likely to be aided by radar and lights on the craft.

The five occupants of the vessel, which is operated by OceanGate Expeditions, have about 96 hours of oxygen available, so they could in theory survive until Thursday, Prof Bachmayer said.

This assumes that there has not been what he described as "a catastrophic failure of some integral part of the structure" of the craft.

Commercial companies produce deep search and rescue vessels that can "mate" or attach to stricken submersible craft to enable a rescue. However, these typically cannot operate at the kind of depths, 3,800 metres, where the missing vessel could be.

For example, a company called JFD produces a submarine rescue vehicle used by the navies in Australia, Singapore and South Korea. These can dive to a depth of 500 metres and "if required this can be increased to 700 metres".

Similarly, the Ministry of Defence in the UK, where Nato’s submarine rescue operations are based, has said the stricken craft is likely to be at depths that "greatly exceed" those at which the organisation can operate.

In any case, Titan is not thought to have a suitable attachment point for a rescue submersible.

"I don’t think there’s any option to transfer people to another submersible. There’s not so many around and there’s no way to safely transfer," Prof Bachmayer said.

He said that craft such as the Titan have lifting points so that they can be carried by crane, offering the possibility, in theory at least, that the vessel could be brought to the surface with cables.

Operate at extreme pressures

Submersibles are designed to operate at extreme pressures, because with every 10 metres of depth, the pressure increases by one atmosphere, or 100 per cent greater than the pressure at sea level.

Most are made from steel, aluminium or titanium and are extremely heavy.

According to CompositesWorld, if they're designed to operate at depths of more than 2,000 metres, maintaining neutral buoyancy is difficult and a type of foam has to be attached to the outside.

But with carbon fibre composites, even a vessel strong enough to operate at depths of many thousands of metres is able to float.

"You have a lighter structure but at the same time carbon fibre typically has a lot of strength," Prof Bachmayer said.

As well as its carbon fibre composite structure, Titan, which was named Cyclops 2 during its design phase, has two titanium hemispheres, one of which has an acrylic viewport, plus a glass fibre composite outer shell.

It should be able to operate at depths of 4,000 metres, but as is typical on a craft people travel in, it has a pressure safety factor of more than two, meaning that the ultimate stress the materials can cope with is more than double the normal working stress

OceanGate Expeditions also has a steel-hulled vessel called Cyclops 1, but this is for depths only down to 500 metres.

The company previously undertook successful expeditions to view the Titanic in 2021 and last year, and planned to continue missions to the wreck each year.

Prof Bachmayer said it was difficult to predict the outcome of the rescue mission.

"I hope for the best," he said. "It’s a big ocean and a lot of different things can go wrong. We just hope for them."