A Retired US Navy submarine captain says survival is not likely for the crew of a missing tourism submarine as the US Coastguard warned there is now less than two days' worth of oxygen left.
The submarine lost contact an hour and 45 minutes into a dive towards the Titanic wreck, according to the US Coast Guard.
The 6.7 metre (22-foot) Titan submersible has the capacity to stay underwater for 96 hours, according to its specifications - giving the five people aboard until early on Thursday before air runs out.
A massive air and sea search began on Sunday night and has been working around the clock for the vessel and the five men aboard, which has so far covered 7600 square miles but had "not yielded any results", Captain Jamie Frederick told reporters at a press conference on Tuesday.
The search has now been expanded to underwater, using sonar and other hi-tech equipment, military authorities confirmed.
Alarmingly, time is running out for the crew on board, with US Coast Guard officials telling the media there are only about 40 hours of breathable air remaining if they are still alive.
“I want to reiterate this is a very complex search and the unified team is working around the clock to bring all available assets and expertise to bear as quickly as possible in an effort to solve a very complex problem,” Frederick said.
He was unable to say how long it would take to get a rescue crew in place if the 6.7-metre submersible is located.
With air estimated to run out early on Thursday, there are grave fears for those on board.
Retired US Navy submarine captain David Marquet told AM survival is not likely for the crew.
"We should remain hopeful as long as possible... but it's a very daunting task. We need to find this submarine and then we have to get it back up to the surface. They can't rescue themselves. They're actually bolted in from the inside," he told AM co-host Ryan Bridge.
"So even if they could get to the surface, they still can't get out of the submarine. They're trapped in this sphere where they're depleting their oxygen and building up carbon dioxide.
"People generally do not come back from the bottom of the ocean. It's happened on extremely rare occasions, but we should prepare ourselves for bad news."
When asked if it's likely something bad has happened with their equipment, which has stopped them from coming to the surface, Marquet said that is a good assumption.
Since search and rescue crews haven't heard signals from the crew from the vessel's underwater telephone to help identify them, Marquet is fearing "for the worst".
On top of that, the crew aren't just facing the challenge of a lack of air, the chilly temperature is also another issue.
"It is below freezing. The water doesn't freeze because it's under a lot of pressure and has a lot of salinity in it, salt in it," he said.
"So it doesn't actually freeze, but it's typically freezing to one or two degrees below freezing."
There are several challenges and obstacles in finding the vessel and saving those aboard, according to experts.
If the submarine experienced an emergency in mid-dive, the pilot would likely have released weights to float back to the surface, according to Alistair Greig, a professor of marine engineering at University College London.
But since there hasn't been any communication, locating a van-sized submarine in the vast Atlantic could prove challenging, he said.
If the vessel is on the ocean floor, a rescue effort would be even more challenging due to the extreme conditions more than 3km below the surface. The Titanic lies 3810m underwater, where light does not penetrate. Only specialized equipment can reach those depths without getting crushed by the massive water pressure.
"It's really a bit like being an astronaut going into space," said Tim Matlin, a Titanic expert. "I think if it's on the seabed, there are so few submarines that are capable of going that deep. And so, therefore, I think it was going to be almost impossible to effect a sub-to-sub rescue."
Five men on board
The submarine - with one pilot and four "mission specialists" onboard - began its dive on Sunday morning.
The five people on board have been identified as Hamish Harding - British billionaire and chairman of aviation company Action Aviation - Shahzada Dawood, 48, and his son Suleman, 19, Paul-Henri Nargeolet - 77-year-old French explorer - and Stockton Rush - the founder and CEO of the vessel's US-based operating company OceanGate.
A friend of one of the missing men told CNN that Nargeolet had been to the Titanic wreck dozens of times.
Mathieu Johann said his friend Nargeolet had a deep knowledge of the Titanic and was a person who accepted the risk that came with these expeditions.
He hoped the search ends "like in the movies, he’ll reappear very quickly to reassure us all.”
The crew aboard the vessel are also having to contend with very tight living spaces, according to promotional materials for the Titan submersible.
NBC News’ Ben Goggin has shared the diagram of the ship, which shows that only one of the passengers is able to fully extend their legs at one time.
US President Joe Biden is “watching events closely” surrounding the missing submersible, the White House’s spokesperson John Kirby said.
"All of us, including the President express our thoughts to the crew on board, as well as to the no doubt worried family members back on shore - and we're just gonna, we're gonna keep looking, keep the search going,” Kirby added.
It's also understood that King Charles has asked to be kept fully up to date on the situation regarding the missing submersible.
The tourist expeditions, which cost $250,000 per person, start in St. John's, Newfoundland, before heading out approximately 640km into the Atlantic to the wreckage site, according to OceanGate's website.
