GEOFF BENNETT: Good evening, and welcome to the "NewsHour."

The U.S. Coast Guard confirmed this afternoon that the missing submersible in the North Atlantic Ocean was destroyed in a -- quote -- "catastrophic implosion."

Its debris was found on the ocean floor, and all five people aboard were killed.

William Brangham begins our coverage.

REAR ADM. JOHN MAUGER, U.S. Coast Guard: This morning, an ROV, or remote-operated vehicle, from the vessel Horizon Arctic discovered the tail cone of the Titan submersible, approximately 1,600 feet from the bow of the Titanic on the seafloor.

WILLIAM BRANGHAM: It was the news no one wanted to hear.

The missing submersible, which disappeared on Sunday on a descent down to visit the wreckage of the Titanic, had been completely destroyed.

U.S. Coast Guard Rear Admiral John Mauger: REAR ADM. JOHN MAUGER: The ROV subsequently found additional debris.

In consultation with experts from within the unified command, the debris is consistent with a catastrophic loss of the pressure chamber.

WILLIAM BRANGHAM: The U.S. Coast Guard and the company that ran the trip, OceanGate Expeditions, expressed their condolences to the families of the five passengers who perished.

They are Hamish Harding, Shahzada Dawood and his son Suleman Dawood, Paul-Henry Nargeolet, and OceanGate CEO and captain of the vessel Stockton Rush.

In a statement, OceanGate thanked the vast international search operation that mobilized over the last few days, saying -- quote -- "The entire OceanGate family is deeply grateful for the countless men and women from multiple organizations who worked so very hard on this mission."

Coast Guard officials said that the nature of the implosion and the depth at which the wreckage sits could make any salvage operation and recovery of the deceased very difficult.

REAR ADM. JOHN MAUGER: This is a incredibly unforgiving environment down there on the seafloor, and the debris is consistent with a catastrophic implosion of the vessel.

WILLIAM BRANGHAM: As those recovery operations continue, and the families grieve their losses, there are sure to be further questions about OceanGate, its safety record, and the overall adventure tourism industry.

In fact, as this saga unfolded over the last few days, past criticisms of OceanGate had reemerged.

Will Kohnen is chairman of the Marine Technology Society's Manned Underwater Vehicles Committee.

Back in 2018, he addressed a critical open letter to the now-deceased OceanGate CEO, Stockton Rush.

And in an interview before today's discovery, he argued that the Titan was not certified to travel down to those depths.

WILL KOHNEN, Marine Technology Society: There are only 10 vehicles in the whole world that can go 4,000 meters or deeper, and all of them are certified, except the Titan.

WILLIAM BRANGHAM: Coast Guard officials couldn't say exactly when the Titan imploded, but said the banging noises heard earlier in the week were seemingly unrelated to this disaster.

The Titan's remains now lie in pieces on the ocean floor less than 2,000 feet from historic wreckage its passengers wanted to see.

For the "PBS NewsHour," I'm William Brangham.

GEOFF BENNETT: Some additional perspective on this accident now and what it could mean going forward.

We're joined again by Jules Jaffe, an oceanographer with the Scripps Institution of Oceanography at the University of California, San Diego.

Thank you for being with us.

And, Jules, when the Coast Guard says that the submersible's debris is consistent with the catastrophic loss of the pressure chamber, what does that mean?

What, based on your vast experience, likely happened?

JULES JAFFE, Research Oceanographer, Marine Physical Laboratory, Scripps Institution of Oceanography: Well, as we know, the vehicle lost contact about one-and-three-quarters hour after it left the surface.

And it was about 2.5 hours to the bottom.

So my conjecture is actually that it was not quite at the bottom, but was probably around 800 or 900 -- 8,000 or 9,000 feet deep.

And from what we understand, the pressure at that depth is around 4,000 pounds per square inch.

So, think about a square inch.

Think about 4,000 pounds.

When you think about the pressure, it's actually coming from all directions.

So the best analogy I could think about was, imagine you have an egg in your hand and you simply crush it.

And I think, honestly, that is what happened to the vehicle.

GEOFF BENNETT: What happens next?

Will there be a recovery effort, or does the ocean depth make that impossible?

JULES JAFFE: Well, we do have these underwater robots that have arms on them.

And I think, in fact, we could probably pick the debris up and load it into, say, a large basket.

These underwater robots are pretty versatile.

And I'm hoping that we can do that and learn really exactly what the failure was, so a future version could ameliorate that problem and make tourist exploration of the deep ocean more accessible and less dangerous.

GEOFF BENNETT: As we just heard in the report, there were questions about safety issues having to do with OceanGate, about the quality of engineering, the level of testing that went into the development.

How does all of that strike you, in light of today's news?

JULES JAFFE: Well, I guess my dad used to say, hindsight is 20/20.

It strikes me, sadly, that perhaps the company was not up to speed and understanding -- remember, we have already made two trips.

They are making about one trip a year, as far as I can tell from my reading the news.

So they did one in 2021.

They did one and 2022.

And here we are on the third trip.

And what happens to anything that's under stress, a mechanical component, is, it fatigues.

And think about the tremendous pressure, and then it relaxes, and the tremendous pressure, and it relaxes.

The other part of the equation that I really worried about, and maybe it's validated, was, when we take planes, we are convinced of their safety.

But we don't always understand that the aerospace industry has strict standards for doing what's nondestructive tests and evaluation.

And they use ultrasonic probes to examine the integrity of the metal components.

If you have ever seen a plane, the wings are flexing, and those guys are world expert on ensuring our safety.

It's pretty clear, sadly, that the people in this company were not up to speed on testing this vehicle and ensuring its safety for such a tragic occurrence as happened probably four days ago, when they lost contact with the surface.

GEOFF BENNETT: Is adventure tourism going to change because of this?

Should it change because of this?

JULES JAFFE: Well, there's another company that makes underwater vehicles that have gone into the Mariana Trench, which is 35,000 feet.

And this one, and I wouldn't call it a shallow application, but it's 12,000 feet.

I think adventure tourism is going to be here to stay.

And I am a supporter of innovation in underwater vehicle development.

But, clearly, we need to be a little more vigilant ensuring the safety and understanding the forces that are on vehicles.

I mean, this design was very new.

It was a carbon fibers combined with titanium.

And I think we need to worry a bit more about the stresses and the fatigue that happens when we make repeated excursions into the deep ocean.

GEOFF BENNETT: Jules Jaffe, thanks so much for your time and for your insights.

JULES JAFFE: My pleasure.