OceanGate Expeditions confirmed that one of its submersibles had gone missing in the Atlantic Ocean while taking passengers to see the famous wreck.

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Here is what we know so far.

Where and when did the submersible go missing?

The submersible went missing on Sunday in the Atlantic, some 435 miles south of Newfoundland, Canada.

The Titan was launched as part of an expedition involving The Polar Prince, an icebreaker that was hired by OceanGate and formerly operated by the Canadian Coast Guard.

The ship ferried dozens of people and the submersible craft to the North Atlantic wreck site, where the Titan was scheduled to make multiple dives.

It is understood from OceanGate that Titan has a 96-hour oxygen supply in case of emergencies meaning only around two days of "life support" remain.

Read more:
Why the hunt for the missing vessel is so diffcult

What is the Titan?

The Titan is a small submersible operated by OceanGate - a US-based company which offers crewed submersibles for industry, research and exploration.

Tickets cost $250,000 (£195,000) for an eight-day trip including dives to the wreck.

According to the company, the Titan is capable of diving 13,120ft "with a comfortable safety margin".

It takes the craft around two hours to descend approximately 12,500ft - where the Titanic wreck lies in a trench in the Atlantic.

The vessel, which weighs around 23,000lbs (10,432kg), operates by pinging back a message every 15 minutes to signal to those ashore that it is safe.

However, Sky News understands that those pings have stopped.

In a May 2021 court filing, OceanGate said the Titan had an "unparalleled safety feature" that assesses the integrity of the hull throughout every dive.

At the time of the filing, Titan had undergone more than 50 test dives, including to the equivalent depth of the Titanic, the company said.

During its 2022 expedition, OceanGate reported that the submersible had a battery issue on its first dive and had to be manually attached to its lifting platform, according to a November court filing.

What about the rescue effort?

US and Canadian ships and planes have been involved in the rescue efforts, but the remote location and depth make the operation particularly challenging.

Also, it is unclear whether the Titan is still underwater or had surfaced and was unable to communicate.

US Coast Guard Rear Admiral John Mauger said: "It is a remote area and it is a challenge to conduct a search in that remote area.

"We are deploying all available assets to make sure that we can locate the craft and rescue the people on board."

The Polar Prince is being used to search the surface where the submersible was launched. Canadian Boeing P-8 Poseidon reconnaissance aircraft and two Lockheed C-130 Hercules aircraft also conducted overflights.

OceanGate Expeditions said it was "mobilising all options" to rescue those on board.

On Wednesday, an internal government memo from the Department of Homeland Security (DHS) said banging sounds had been detected by sonar devices every 30 minutes on Tuesday.

Four hours later, after additional sonar devices were deployed, banging was still heard, the memo said.

The US Coast Guard said remote underwater vehicles were redeployed in response to the reports of banging but that the searches yielded negative results so far.

What do we know about the people on board?

• Hamish Harding

British billionaire Hamish Harding, 58, was confirmed as one of the passengers by his stepson Brian Szasz, who said on Facebook that his stepfather was in his "thoughts and prayers".

Mr Harding is the current chairman of Action Aviation - a sales and operations company that offers a range of services in the business aviation industry.

Posting on social media before the trip, Mr Harding said he was joining OceanGate Expeditions - the company that supplied the vessel - as a mission specialist.

He wrote that due to bad weather in Newfoundland, Canada, the expedition was likely to be the first and only manned mission to the Titanic in 2023.

Based in the United Arab Emirates - where Action Aviation headquarters is based - Mr Harding described himself on social media as a world explorer.

He holds the Guinness world record for the fastest circumnavigation of the Earth via the North and South Poles by an aircraft - 46 hours, 40 minutes and 22 seconds.

In 2016, Harding accompanied former astronaut Buzz Aldrin to the South Pole, when Aldrin became the oldest person ever to reach the Antarctic region, at 86.

Last year, he also took part in the fifth human space flight by Blue Origin - an American aerospace company founded by Jeff Bezos.

Jannicke Mikkelsen, an explorer and friend of Hamish Harding, told Sky News she believed Mr Harding would be an "important asset" to the others in the submersible.

"He will go through the emergency checklists and procedures together with the captain of the submersible," she said.

"He will also be a good inspiration to the rest of the team to keep calm. I really believe Hamish is the one that can help lead this team - because he has been in tricky situations in the past on expeditions.

She added: "I'm terrified if they are stuck at the bottom of the ocean with 96 hours of air and not able to get back to the surface - this is what I fear the most."

• Stockton Rush

Stockton Rush is chief executive and founder of OceanGate Inc - a company that provides crewed submersible services to enable researchers and explorers to access the oceans' vast resources.

Having trained as a pilot, he became the youngest jet transport rated pilot in the world at the age of 19.

He is also a founder and member of the board of trustees of non-profit organisation OceanGate Foundation, which aims to catalyse emerging marine technology to further discoveries in marine science, history, and archaeology.

In an interview with Sky News back in February, Mr Rush spoke about visiting the Titanic wreck.

"What really strikes you is how beautiful it is," he said. "You don't normally see that on a shipwreck.

"It is an amazingly beautiful wreck."

When asked if they can go inside the wreckage, Mr Rush said: "You can see inside, we dipped down and saw the grand staircase and saw some of the chandeliers still hanging.

"Next year we are hoping to send a small robot inside but for now we stay on the outside."

• Paul-Henri Nargeolet

Paul-Henri Nargeolet is a former commander who served in the French Navy for 25 years.

During his service, he became the captain of the deep submergence group of the navy.

After leaving the navy he joined the French Institute for Research and Exploitation of the Sea, according to The Five Deeps Expedition - a company that assembles scientists, engineers and submersible operators for missions.

Mr Nargeolet has already led several expeditions to the Titanic site and has been involved in numerous scientific and technical expeditions around the world.

The first British diver to see the Titanic wreck paid tribute to his friend, saying he is an "extraordinary explorer and an incredible individual".

Dik Barton made 22 dives to the wreck to recover artefacts when he was head of operations with RMS Titanic Inc, a US firm which salvaged the site, and worked with Mr Nargeolet on the dives.

Mr Barton said the group on the missing trip had "good leadership".

"He is the kind of man who will keep them calm, but it's not easy in a tube at the bottom of the ocean," he said.

"It's tragic. He is an extraordinary explorer and an incredible individual and he knows the wreck better than anybody I know.

"It's an incredibly hostile environment at the depths we are talking about. The pressure down there is 2,500lbs per square inch, that's the equivalent of two adult elephants on your thumbnail.

"If something goes wrong, it goes wrong very quickly."

• Shahzada Dawood and his son Suleman

Pakistani businessman Shahzada Dawood and his son Suleman, who are both British citizens, are also on board, their family said in a statement.

"We are very grateful for the concern being shown by our colleagues and friends and would like to request everyone to pray for their safety," they added.

The Dawoods belong to one of Pakistan's most prominent families, whose eponymous firm invests across the country in agriculture, industries and the health sector.

Mr Dawood, 48, also currently serves as the vice chairman of the board of Engro Corporation - a Pakistan-based conglomerate operating across a number of sectors including fertiliser and chemical production.

The UK-based businessman is also a trustee at the SETI Institute - a Silicon Valley not-for-profit working in space exploration.

Suleman, 19, is currently at university, his family said.