A missing submersible near the Titanic wreck had only hours of air left today, the fifth day of a huge search across the remote North Atlantic.

The Titan, run by US-based OceanGate Expeditions, lost contact with its support ship on Sunday morning during a dive to the old shipwreck. It had 96 hours of air, the company said, which would run out some time this morning. That depends on things like its power and how calm the people inside are, experts say, and if the Titan is still whole.

A Canadian vessel sent a robot to the ocean floor to look for the Titan, the US Coast Guard said this morning on Twitter.

Rescue teams from many countries and loved ones of the five people in the Titan felt hopeful when the US Coast Guard said yesterday that Canadian planes had heard undersea sounds with sonar buoys earlier that day and on Tuesday.

But the Coast Guard said robots looking where the sounds came from had found nothing, and officials warned the sounds might not be from the Titan.

“You always have hope when you’re searching for someone,” Coast Guard Captain Jamie Frederick said yesterday, saying they were not sure about the sounds.

The French ship Atalante, with a diving robot that can reach the Titanic wreck at about 12,500 feet (3,810 metres) deep, had got to the search area by today.

The Atalante was first using a device to make a clear map of the seabed so the robot’s search could be more focused, the French marine research institute Ifremer said.

The robot, Victor 6000, has arms that can be moved remotely to free or hook a stuck craft and pull it up. The US Navy is also sending a special system to lift big things under the sea.

Sea adventure

The Titanic, which hit an iceberg and sank in 1912 on its first trip, killing more than 1,500 people, is about 900 miles east of Cape Cod, Massachusetts, and 400 miles south of St. John’s, Newfoundland.

The Titan had its pilot and four others on a deep-sea trip to the shipwreck, ending a tourist adventure that Ocean Gate charges US$250,000 per person.

The passengers were British billionaire and adventurer Hamish Harding, 58, and British business tycoon Shahzada Dawood, 48, from Pakistan, with his son Suleman, 19.

French Titanic expert Paul-Henri Nargeolet, 77, and Ocean Gate founder and CEO Stockton Rush were also on the sub. Rush’s wife is related to two Titanic victims.

“We’re very worried, we barely sleep,” said Mathieu Johann, Nargeolet’s editor at Harper Collins.

Sean Leet, who runs a company that co-owns the support ship, the Polar Prince, said on Wednesday they did everything right before the sub lost contact.

“There’s still air left on the sub, and we’ll keep hoping until the end,” said Leet, CEO of Miawpukek Horizon Maritime Services.

Some people questioned Titan’s safety in 2018 at a submersible industry meeting and in a lawsuit by OceanGate’s former marine operations head, which was settled that year.

Finding the Titan would be hard, and getting it back would be harder.

If the sub had come back up, it would be hard to see in the sea and it is locked from the outside, so the people inside can’t get out without help.

If the sub had come back up, it would be hard to see in the sea and it is locked from the outside, so the people inside can’t get out without help.

If Titan is at the bottom of the ocean, a rescue would have to deal with the huge pressures and total darkness there. British Titanic expert Tim Maltin said it would be “very hard to do a sub-to-sub rescue” on the ocean floor.

It might also be hard to find the Titan among the wreck.

“There are a thousand things that size if you look at the Titanic debris field,” said Jamie Pringle, a forensic geoscientist at Keele University in the UK. “It might be a never-ending job.”