Updated June 22, 2023 at 6:23 PM ET

All five passengers aboard the missing Titan submersible have died following a "catastrophic implosion of the vessel," the U.S. Coast Guard said Thursday.

Speaking at a news conference in Boston, Rear Adm. John Mauger said the debris found by a remotely operated vehicle on the sea floor near the wreck of the Titanic indicated the crew and passengers likely died from the failure of the craft.

"The debris is consistent with the catastrophic loss of the pressure chamber," he said. "Upon this determination, we immediately notified the families ... I can only imagine what this has been like for them. And I hope that this discovery provides some solace during this difficult time."

OceanGate, the company that developed the submersible, said officials "now believe that our CEO Stockton Rush, Shahzada Dawood and his son Suleman Dawood, Hamish Harding, and Paul-Henri Nargeolet, have sadly been lost,"

Coast Guard officials said they will begin to withdraw vessels from the scene over the next 24 hours but added that remote operations will continue on the sea floor.

When asked about the likelihood of recovering the bodies, Mauger said he does not have an answer and noted the "incredibly unforgiving environment" of the sea floor.

Earlier Thursday rescue teams hunting for the missing submersible uncovered a field of debris near the site of the wrecked ocean liner, the Coast Guard said.

Here's a guide to what we know.

What do we know about the debris field?

The Coast Guard said that the debris field was uncovered by an ROV deployed by the Canadian ship Horizon Arctic, which had reached the sea floor early Thursday.

Experts say the seabed around the Titanic is littered with bits of the wreck, which shows tell-tale signs of its age, including the effects of an iron-eating bacteria.

The Coast Guard said that maritime surveillance planes operated by Canada detected underwater sounds late Tuesday, then again on Wednesday.

Various underwater search efforts were moved to the location of the noise to discover its source, but the Coast Guard said efforts "yielded negative results" up until news of the debris field.

As of Wednesday, underwater acoustic experts from the U.S. Navy were still analyzing the sounds, which one expert described as "banging noises."

The Coast Guard and other experts with knowledge of the search warned that the sounds were not necessarily proof of life.

"You have to remember that it's the wreck site of the Titanic, so there is a lot of metal and different objects in the water around the site," Mauger said in an interview with CBS News on Wednesday morning.

What kind of equipment is being used in the search?

The Coast Guard says that the data from the Canadian aircraft, a P-3 Orion, nevertheless served as a focus point for its unified search efforts.

The remoteness of the location and the size of the search area — extending 10,000 miles on the surface and 2.4 miles down to the ocean floor — complicated efforts to locate the vessel and its passengers. Thursday's weather, at least, may have proved more favorable to search crews, with winds slowing to 14 mph and wave swells dropping around 4 to 5 feet.

In addition to the remote-operated vehicles deployed by Horizon Arctic, a second deep-diving ROV, deployed by the French vessel L'Atalante, was searching for the Titan.

The design of the Titan means that only those outside the vessel can unseal it: if it had risen to the surface the passengers would have required outside help to escape.

The unified search command led by the Coast Guard has been criticized by industry experts and U.S. lawmakers who say the teams didn't send equipment to the site early enough.

Richard Garriott de Cayeux, president of the Explorers Club, tweeted that members of the research group continually offered their expertise and equipment — including a deep-diving ROV with the ability to attach a lift cable to the Titan — but were not approved to send the equipment until Wednesday, putting the estimated arrival time hours behind when the Titan's emergency oxygen supply was due to expire.

The experience of Pelagic Research Services, the group that provided the ROV aboard Horizon Arctic, shows the time-consuming nature of getting specialized equipment to the deep sea.

In a statement provided to NPR, Pelagic said it was contacted by the search team on Monday, assembled its ROV crew and equipment within 23 hours, received U.S. Air Force transport to St. John's in Newfoundland, Canada, mobilized onto the Canadian ship Horizon Arctic, and still only was able to deploy their ROV by early Thursday morning.

The ROV uncovered the debris field within hours of that deployment.

But the arrival of any of the search and rescue vessels would not have made any difference if the implosion occurred upon the sub's initial descent on Sunday.

When would the sub's oxygen supply have run out?

At the beginning of the search on Sunday, officials estimated the submersible, if still fully functional, contained about 96 hours of reserve oxygen. At a 1 p.m. ET press conference on Wednesday, the Coast Guard estimated that supply was down to about 20 hours.

That means the the oxygen on board the Titan would have run out early Thursday morning, when crews were continuing search-and-rescue efforts on the assumption that the people on board were still alive.

When and where did the sub go missing?

Titan lost contact with its support ship — a Canadian research vessel called Polar Prince — an hour and 45 minutes after it first entered the water on Sunday around 8 a.m. ET.

At that point, it was already more than halfway down to the Titanic's wreck on the Atlantic's ocean bed, roughly 900 miles east of Cape Cod in Massachusetts.

The Coast Guard said it was first notified of the missing vessel at 5:40 p.m. ET, nearly three hours after the Titan was expected to resurface at 3 p.m. ET.

Who was on board?

The people on board Titan included pilot Stockton Rush, the head of OceanGate, the company that developed the submersible; Paul-Henri Nargeolet, a French underwater wreck expert who has written about the Titanic and visited the wreck dozens of times; a British entrepreneur Hamish Harding; and father-son Pakistani nationals Shahzada and Suleman Dawood.

A former passenger of the Titan described the vessel as like being in a "minivan without seats" and says its interior design relies on "off-the-shelf parts," including a video game controller for steering.

What was the sub's mission?

The missing vessel is owned by OceanGate, a company based in Washington state that's become a major chronicler of the Titanic's decay.

In May, OceanGate shared the first-ever full-size digital scan of the wreck site, which is slowly succumbing to a metal-eating bacteria and at risk of disintegrating in a matter of decades.

For $250,000 a person, the company promises tourists an underwater voyage to explore the remains of the Titanic from the seafloor. From St. John's, explorers travel 380 miles offshore and 2.4 miles below the surface. A full trip can take eight days and include multiple dives.

If successful, the dives offer a glimpse of what's left of the 1912 crash into an iceberg, which took the lives of all but 700 of the Titanic's 2,200 passengers and crew.

Did anyone warn OceanGate that the Titan wasn't safe?

Years before the Titan went missing, OceanGate faced several complaints and warnings about the safety of its submersible vessels.

Records from a 2018 lawsuit show that the company's former director of marine operations, David Lochridge, flagged potential safety issues with the Titan as it was under development in 2015.

Lochridge was particularly concerned about the company's lack of testing on the Titan's 5-inch-thick carbon fiber hull, which employed an experimental design developed in collaboration with NASA. He also said that the Titan's port window was only designed to withstand depths of about 4,200 feet — far shallower than the 13,000-foot depth of the Titanic.

OceanGate responded in legal filings by saying it relied on acoustic testing "better suited" to detect safety issues. The company fired and sued Lochridge, accusing him of breaching his contract.

Separately, but in the same year the lawsuit was settled, the chairman of the Marine Technology Society's Submarine Group wrote a letter to OceanGate saying 38 industry experts had "unanimous concern" about the Titan's lack of adherence to industry standards.

"We have submarines all over the world diving at 12,000 to 20,000 feet every day of the year, for research. We know very well how to design these machines and operate them safely," the chairman, Will Kohnen, told NPR's Morning Edition on Wednesday.

How did OceanGate respond to warnings about Titan's safety?

OceanGate has seen at least two documented safety incidents with the Titan after these warnings.

During a 2022 expedition, OceanGate reported that its sub had experienced a battery issue during a dive and had to be manually reattached to its lifting platform, court filings show.

In the same year, the vessel lost contact with its surface crew for nearly five hours during a dive, according to CBS correspondent David Pogue, who was observing the mission for a journalistic report on the company.

Pogue reported that a waiver for passengers of the Titan clearly states the vessel has not been approved or certified by any regulatory body.

Rush, OceanGate's founder, said in a 2019 interview that the commercial submarine industry's regulations stood in the way of progress.

"It's obscenely safe because they have all these regulations," Rush told The Smithsonian Magazine. "But it also hasn't innovated or grown."

NPR's Willem Marx, Ayana Archie and Juliana Kim contributed reporting.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

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