In 2000, Dr. Michael Guillen, then an ABC News correspondent, was filming from the wreck of the Titanic when his vessel became trapped in the propeller.

"When we collided with the propeller, and I started seeing those big chunks of metal raining down on us … the first reaction I had was, 'This can't be happening,'" he recalled to ABC News on Tuesday.

"We got caught by this underwater turn and just drove us right into the blades," Guillen said.

"This voice came into my head and said, you know, 'This is how it's going to end for you,'" he recalled. "I'll never forget those words."

"I'm very aware of what these poor souls on board the ship the Titan are experiencing," he said. "I am just heartbroken about it."

At the request of French President Emmanuel Macron, a French ship named Atalante is diverting to the area of the missing submissive and should reach the area Wednesday night.

The ship has an exploration robot that can dive up to 4,000 meters, according to a spokesman for France's Ifremer Institute.

Per Wimmer, an explorer and global financier, told ABC News he was "shocked" and "horrified" to hear of the missing submersible.

"It felt very personal. … I've been wanting to go down to the Titanic for more than a decade," Wimmer said.

He estimated that there's been between 150 and 200 missions to the Titanic.

There "are very, very few submersibles in the whole world that can go down to the depth of Titanic, which sits at 3,800 meters, or about 12,000 feet," Wimmer said. "It's very deep -- most submersibles can go down to about 1,000 meters."

"It's a race against time, because there's only 96 hours of oxygen on board. And after that, if you haven't reached the surface, you starve of oxygen," he said.

"Our best hope at the moment is that the safety mechanism will be activated," he said. "It is supposed to be able to float to the surface, little by little, and then they can open the hatch and hopefully get out again. That is the only hope we have, because you do not have enough time to get another submersible that can go that deep."

-ABC News' Dom Proto

Renowned explorers and a father-son duo were among the five people aboard a submersible that disappeared in the Atlantic Ocean on Sunday while touring the Titanic wreckage, ABC News has learned.

ABC News has confirmed the identities of those aboard as: Shahzada Dawood, a Pakistani businessman, and his son Suleman Dawood; Hamish Harding, a British businessman, pilot and space tourist; Paul-Henri Nargeolet, a French diver and Titanic expert; and Stockton Rush, the CEO and founder of the submersible's Washington-based operator, OceanGate Expeditions.

-ABC News' Victoria Beale, Miles Cohen, Laryssa Demkiw and Anna Rabemanantsoa

OceanGate co-founder Guillermo Söhnlein is coming to the defense of late CEO Stockton Rush, one of those killed in the implosion of Titan, after criticism from director James Cameron, and others, who said the sub's carbon-fiber hull was dangerous.

"In this kind of community, there are completely different opinions and views about how to do things, how to design submersibles, how to engineer them, build them, how to operate in the dives," Söhnlein told the U.K.'s Times Radio on Friday. "But one thing that’s true of me and the other experts, is none of us were involved in the design, engineering, building, testing or even diving of the subs. So it’s impossible for anyone to really speculate from the outside."

Söhnlein co-founded OceanGate in 2009 with Rush and led several dives in the early days of the company. He left OceanGate in 2013, when Rush took over as CEO, but maintained a friendship and spoke to Rush just weeks before the doomed expedition, he said on Facebook.

Cameron, who not only directed the Oscar-winning film "Titanic" but is a prolific ocean explorer, criticized the use of a carbon-fiber hull in the construction of Titan, saying it was only a matter of time before it cracked under the pressure from repeated dives. Rush, in the past, defended its use, saying it had a better strength-to-buoyancy ratio than titanium.

"I was involved in the early phases of the overall development program during our predecessor subs to Titan, and I know from firsthand experience that we were extremely committed to safety and risk mitigation was a key part of the company culture," Söhnlein told Times Radio Friday.