Search operations for missing Titanic sub continue

Nautical experts, the U.S. and Canadian navies and the U.S. Coast Guard are scrambling to get the necessary equipment and personnel to help locate the five people in the tour submersible that left Sunday to view the wreckage of the Titanic.

But even with their specialized tech, search and rescue teams are facing major obstacles that could make saving the people onboard extremely difficult, according to a former Navy submarine commander.

Retired Capt. David Marquet told ABC News on Monday that this type of rescue operation is complicated because there are no U.S. or Canadian underwater vessels nearby that can go as deep as the Titanic wreckage, which sits 13,000 feet below the ocean's surface. The ocean is also pitch-black at that depth, creating another major problem, he said.

"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."

However, on Wednesday a U.S. Navy official told ABC News it had sent a portable crane system that can reach 20,000 feet deep to St. John’s, Newfoundland, so it can be welded onto a ship to take it to the search area for the missing submersible.

It could be days before the crane can be used because the Navy has not yet contracted a ship for use with the FADOSS system.

“Our estimate is (an) approximately 24 hours around the clock operation to weld it and secure it to the deck of the vessel prior to getting underway,” the official said.

The submersible vessel is designed to hold 96 hours of oxygen, Rear Adm. John Mauger, commander of the U.S. Coast Guard First District, told reporters Monday. The air is predicted to run out Thursday morning, according to the Coast Guard.

On Monday, the Coast Guard said it had conducted a search of the surface of the water for the missing submersible in conjunction with the Canadian Coast Guard and Canadian Armed Forces.

The Bahamian research vessel Deep Energy, which specializes in pipe-laying and has remotely operated vehicle capabilities, arrived on Tuesday morning to help with the search.

The Pentagon said Tuesday that three U.S. Air Force C-17 cargo aircraft were transporting commercial equipment from Buffalo, New York, to St. John’s, Newfoundland, to aid the rescue efforts.

Additionally, the Navy announced it was sending experts and a Flyaway Deep Ocean Salvage System, or FADOSS, which it described as a “motion compensated lift system designed to provide reliable deep ocean lifting capacity for the recovery of large, bulky, and heavy undersea objects such as aircraft or small vessels.”

The New York Air National Guard’s 106 Rescue Wing out of Westhampton, which flies out a version of the C130 that specializes in search and rescue, was deployed to help with the search, New York Gov. Kathy Hochul said Tuesday.

The 106th flies fixed-wing search and rescue aircraft and rescue helicopters and has a unit of pararescue jumpers who are trained to rescue people on sea and land, according to the governor's office.

Early morning on Wednesday, Canadian aircraft with sonar capabilities detected "underwater noises" in the search area. Coast Guard crews said they did not know what was causing the noise.

If the search parties can locate the submersible and lower a cable, it will be extremely difficult to safely navigate the waters and attach it, Marquet said.

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

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.

The 21-foot submersible lost communication with the mainland 1 hour and 45 minutes after it embarked on its tour of the Titanic wreckage on Sunday.

In ABC News’ interview with Marquet earlier this week, he said if the five people are still alive, their best course of action would be 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' Luis Martinez and Aaron Katersky contributed to this report.