Earlier this month, a submersible called the Titan dove into the ocean to see the wreckage of the Titanic. The sub went missing and after a four-day-long search, U.S. Coast Guard Rear Adm. John Mauger said the sub experienced a “catastrophic implosion,” according to CNN.

Stockton Rush, Shahzada Dawood, Suleman Dawood, Hamish Harding and Paul-Henri Nargeolet are presumed dead, per NBC News. The day the sub went missing U.S. Navy personnel heard what was thought could be the sound of the implosion, and then later a debris field was found, according to The Wall Street Journal.

It’s believed the sub imploded the Sunday it went missing.

James Cameron has visited Titanic wreckage 33 times. Here’s what he said about the Titan

James Cameron, who has taken 33 dives down to the Titanic wreckage and has helped design a submersible, told Reuters, “OceanGate shouldn’t have been doing what it was doing. I think that’s pretty clear. I wish I had been more vocal about it, but I think that I was unaware that they weren’t certified.”

On Times Radio, OceanGate co-founder Guillermo Söhnlein mentioned Cameron by name and addressed some of his public comments.

“There are completely different opinions and views about how to do things, how to design submersibles, how to engineer them, how to build them, how to operate in the dives,” Söhnlein said to Times Radio. “But one thing that’s true of me and every other expert who’s been talking is none of us were involved in the design, engineering, building or testing or even diving of the subs. So it’s impossible to speculate for anyone to really speculate from the outside.”

“I know from firsthand experience that we were extremely committed to safety,” Söhnlein said to Times Radio. “And safety and risk mitigation was a key part of the company culture.

Söhnlein co-founded OceanGate Expeditions with Rush. He served as the company’s CEO and then left the company in 2013. He was involved in the development of “predecessor subs to the Titan,” according to the Los Angeles Times.

More than three dozen people in the submersible craft industry signed a joint letter in 2018, “warning of possible ‘catastrophic’ problems with the submersible’s development and its planned mission to tour the Titanic wreckage,” per The New York Times. The letter was sent to OceanGate CEO Rush, who was on the Titan when it’s believed it imploded.

What did James Cameron say about the Titan sub?

Cameron told Reuters the day after the sub went missing, a Monday morning, he heard that the sub lost communication and tracking. He described the tracking system as a “fully autonomous system.”

After Cameron talked to more people on Monday, he said he heard that there was a “loud bang on the hydrophones” and at that point, he said he knew the sub imploded.

The “Titanic” director said he declined an invitation to go diving this season with Rush, per NPR. He said the Titan’s carbon-fiber hull was “fundamentally flawed.”

“Contiguous materials such as steel, titanium, ceramic or acrylic” are typically using for making pressure hulls, Cameron told Reuters.

The Coast Guard’s Marine Board of Investigation is investigating the Titan’s implosion, according to the Deseret News.