Missing Titanic submersible live updates: Texts show OceanGate CEO dismissed concerns

Rescuers racing against the clock to save the five people trapped in a tourist submersible nearly two miles deep in the Atlantic Ocean are facing major obstacles that could make saving the people onboard extremely difficult, according to a former U.S. Navy submarine commander.

Retired Capt. David Marquet told ABC News on Monday that this type of rescue operation is complicated because there aren’t nearby U.S. or Canadian underwater vessels that can go as deep as the Titanic wreckage, which sits 13,400 feet below the ocean’s surface. Also, the ocean is pitch black at that depth.

"The odds are against them," Marquet said. "There's a ship in Boston that has this ability to either lower cable and connect to it or have a claw. It's still a thousand miles away."

Even if a vessel was able to locate the submersible and lower a cable, it’s extremely difficult to safely navigate the waters and attach it, according to Marquet.

"You've got to get it exactly right," he told ABC News. "It's sort of like ... getting one of those toys out of those arcade machines. In general, you miss."

Rescuers do have one advantage, Marquet said, as weather conditions off the coast of Newfoundland are not rough and will not disturb any boat or vessel there.

Marquet added that if the five people aboard are still alive, they would be asked to sleep to conserve their oxygen.

"We would put the vast majority of the crew to sleep because that's when you're using the least amount of oxygen and you're expelling the least amount of carbon dioxide," he said.

-ABC News' Sam Sweeney and Ivan Pereira

A submersible on a tour of the Titanic wreckage was reported overdue by its operator OceanGate Expeditions on Sunday, prompting the United States Coast Guard to launch a search and rescue effort for the 22-foot, 23,000-pound vessel.

Designed with life support to sustain five crew members for 96 hours, the submersible would need to be rescued in three days to save its five passengers, according to the Coast Guard.

Stockton Rush founded Washington-based OceanGate in 2009 to make deep-sea exploration more accessible to scientists and tourists. Fourteen years, more than 200 dives and three submersible designs later, the company now finds itself in a desperate search to recover the submersible carrying five people aboard that’s gone missing off the coast of Newfoundland, Canada.

OceanGate confirmed Monday it had lost contact with a submersible, saying in a statement: "We are exploring and mobilizing all options to bring the crew back safely. Our entire focus is on the crewmembers in the submersible and their families. We are working toward the safe return of the crewmembers."

Here's what we know about the submersible.

-ABC News' Peter Charalambous and Sam Sweeney