James Cameron says the Titan passengers probably knew the submersible was in trouble

A "catastrophic pressure implosion" killed all five passengers aboard the Titan submersible, the U.S. Coast Guard said Thursday, somberly solving a mystery that had captivated the public all week.

Some experts, however, weren't surprised — including film director and deep-sea explorer James Cameron. The Titanic director is criticizing the safety of the vessel that was to have explored the wreckage of the Titanic in the depths of the North Atlantic and comparing the cause of the accident to the ocean liner's historic disaster.

In a series of television interviews, Cameron said he had suspected all week that the Titan had imploded on Sunday. (A senior Navy official has confirmed to NPR that an acoustic listening system detected such sounds on Sunday afternoon.)

Cameron told ABC News that he believes the Titan's hull began to crack under pressure and that its inside sensors gave the passengers a warning to that effect.

"We understand from inside the community that they had dropped their ascent weights and they were coming up, trying to manage an emergency," he said.

The Titanic director is no stranger to deep-sea exploration. He has made a whopping 33 dives to the shipwreck himself, even calculating that he's spent more time on the Titanic than its own captain did a century ago.

He also dove the Mariana Trench — the deepest-known point on Earth, about three times deeper than the Titanic wreck site — in 2012, in a 24-foot cylindrical submersible he spent seven years building.

"I think it's the explorer's job to go and be at the remote edge of human experience and then come back and tell that story," he told NPR that year.

Cameron and many others in the deep submergence community had long been concerned about the vessel's safety and OceanGate's experimental approach, he said on Thursday, lamenting that the company had ignored experts' calls to undergo a standard certification process.

"I'm struck by the similarity of the Titanic disaster itself, where the captain was repeatedly warned about ice ahead of his ship, and yet, he steamed up full speed into an ice field on a moonless night, and many people died as a result," Cameron said. "And for a very similar tragedy, where warnings went unheeded, to take place at the same exact site, with all the diving that's going on all around the world, I think it's just astonishing, it's really quite surreal."

Cameron stressed that deep submergence diving is "a mature art," with very few accidents when it began in the 1960s and an even better safety record now, thanks in large part to the certification protocols that almost all such vehicles follow — except this one.

It's clear that OceanGate "shouldn't have been doing what it was doing," he told Reuters, adding that he had declined an invitation from CEO Stockton Rush to go diving with them this season.

Cameron described OceanGate's use of a carbon-fiber hull as "fundamentally flawed" and said he had warned another company several years ago against using that same design principle. He said he regrets not speaking up more this time around.

"Now there's one wreck lying next to the other wreck," he said, "for the same damn reason."

Cameron was convinced the vessel had imploded on Sunday

Cameron told CNN that he was out on a ship himself on Sunday, so didn't hear about the missing vessel until Monday morning.

He said he immediately made some calls to his network and found out within about half an hour that the Titan had lost communications and tracking simultaneously.

"The only scenario that I could come up with in my mind that could account for that was an implosion, a shockwave event so powerful that it actually took out a secondary system that has its own pressure vessel and its own battery power supply, which is the transponder that the ship uses to track where the sub is," Cameron said.

Later that day, Cameron got more information "that was probably of a military origin, although it could have been research" suggesting there had been some sort of loud noise on Sunday consistent with that of an implosion.

"That seemed to me enough confirmation that I let all of my inner circle of people know that we had lost our comrades, and I encouraged everybody to raise a glass in their honor on Monday," he said.

Cameron said it was difficult to watch the frantic search play out over the next few days, knowing it was futile but hoping he was wrong. He especially feels for the families who had to go through it.

The deep submergence community is small, Cameron stressed. He said he's known Paul-Henri Nargeolet, the "legendary" French submersible pilot who was one of the five people on board, for 25 years.

"For him to have died tragically in this way is almost impossible for me to process," he added.

Cameron's safety concerns echo those of other experts

Cameron reiterated concerns that others from within and beyond OceanGate had been raising as far back as 2018, namely about the vessel's carbon fiber hull and the company's decision not to have it certified by a third-party agency.

"I think it was unconscionable that this group did not go through that rigorous process," he told CNN.

He told the BBC he believed they hadn't done so because "they knew they wouldn't pass."

OceanGate said in a 2019 blog post that the certification process only assessed the vessels themselves — not operational safety, which it took seriously. It also said regulation was preventing innovation, echoing comments Rush told Smithsonian Magazine that same year.

Cameron said he personally never believed in the sort of carbon fiber cylindrical hull that the company used, telling Reuters it was a "horrible idea" that "just sounded bad on its face."

Pressure hulls should be made out of contiguous material like steel, titanium, ceramic or acrylic, he explained, in order to do modeling and finite element analysis to "understand the number of cycles that it can take." That's not the case with a composite material, like carbon fiber, made of two different materials blended together.

"And so we all knew that the danger was delamination and progressive failure over time with microscopic water ingress and ... what they call cycling fatigue," he added. "And we knew if the sub passed its pressure test it wasn't gonna fail on its first dive ... but it's going to fail over time, which is insidious. You don't get that with steel or titanium."

Cameron told ABC News that the risk of implosion is "first and foremost in our minds as engineers."

When creating the submersible he would eventually take to the Challenger Deep (the deepest part of the Mariana Trench), Cameron said his team spent more than three years working on a computerized model of the hull before even building it, let alone repeatedly pressure testing it.

He remembers first hearing about a move toward composite hulls around this time, when British entrepreneur and astronaut Richard Branson was working on his own competing sub to dive to the Challenger Deep (the mission was later shelved).

"I told those guys ... 'Somebody's going to get killed in that sub or in a sub like it,' " Cameron said.

Titanic dives can be dangerous no matter the vessel

Comparing OceanGate to his Titanic dives is like "apples and oranges," Cameron told ABC News.

He dove with Russian submersibles that he said used "very, very well-understood design methodologies" and had a "flawless operating record" throughout their career.

While he always had confidence in the vessel, he acknowledged that the Titanic shipwreck is a hostile and dangerous site to dive.

"You've got this eight-story, 10-story-high structure with overhanging metal structures," he explained. "It's a twisted mess, you can get entangled."

Cameron said he always used a two-sub system, so that if one of the vessels got ensnared the other would be there to help manage the situation.

He went to similarly great lengths to prepare for his record-breaking Challenger Deep dive 7 miles down in the ocean, as he explained to NPR in 2013.

That expedition involved using two 536-pound weights to pull his submersible down, spending about three hours on the ocean floor and then disconnecting the weights to rise back up.

Cameron said there's always a sigh of relief when things work the way they should.

"We treated it like a space mission, and you have to go in with a lot of redundancy in the way you design it," he told NPR's Melissa Block. "So I wasn't surprised when it worked. But you're always a little bit relieved, because the alternative is not pretty."