Robert Blasiak - an ocean researcher with the Stockholm Resilience Centre - outlined the tough conditions facing the search teams.

"The ocean on average is about four kilometres deep so this [submersible] is at great depth," Blasiak told the BBC.

He added that light only penetrates up to about one kilometre into the ocean's surface, so that's in 'pitch black and water pressures of about 400 atmospheres'.

Blasiak described the challenges for OceanGate's Titan submersible craft in reaching the wreck of the Titanic:

The US Coast Guard has confirmed there were five people onboard the submarine vessel, which it says has been missing since Sunday morning local time.

In a series of Twitter posts, external, the Coast Guard described the submarine as being 21 feet (6.4m) in length.

It went missing more than 24 hours ago, on Sunday morning, about one hour and 45 minutes into its dive.

Both US and Canadian naval surveillance aircraft are currently searching for it, including a highly-sophisticated P8 Poseidon aircraft with underwater detection capabilities.

Stay with us for updates from the commander of the First Coast Guard District, Rear Admiral John Mauger, expected at a 16:30 EST (21:30 BST) news conference in Boston.

Megan Moncrief, a travel insurance expert at Squaremouth, tells the BBC that standard travel insurance policies would not cover an excursion like a submarine dive.

"This is an especially high-risk activity that would require special underwriting. A policy for this would likely need to be placed by the excursion company's insurance agent," she added.

OceanGate, which organised the Titanic dive, says personal travel insurance is not included in the $250,000 (£195,000) ticket price.

Beth Timmins
Business reporter

Image source, OceanGate

I spoke with former aerospace engineer, and OceanGate chief executive, Stockton Rush, back in 2017.

He told me a trip to explore the Titanic for eight days would cost $105,129 (£82,000). It was the first time a journey that deep had been opened up to tourists.

Now the expedition costs $250,000 per person to travel around 400 miles into the Atlantic to the wreckage site.

When he launched the tour, he told me he'd booked out to the same nine guests who’ve booked up Virgin Galactic's maiden flight.

Mr Rush told me he'd always wanted to be an astronaut, but after completing an aerospace degree and engineering work on the US fighter programme, he was told that his 20/25 eyesight wouldn’t allow him to be an air force pilot.

As a keen scuba diver, he decided to launch submersible trips to depths that were previously the remit of government submarines.

Among his previous OceanGate guests are Everest climbers, nautical archaeologists and filmmakers. He's also had travellers as old as 92 and and as young as 12 on his vessels.

Rush has yet to comment on the missing vessel.

Image source, Getty Images

The Titanic hit an iceberg on 14 April 1912, during her maiden voyage from Southampton, England, to New York City in the US.

More than 1,500 of the 2,200 passengers drowned that day, in the deadliest sinking of a single ship up to that time.

US and UK inquiries into the sinking found, among other things, that the ship's lifeboats were not filled to capacity and cut backs to Titanic's design may have made things worse.

The actions of both survivors and those who perished have entered into folklore, with the event providing the basis for the disaster film genre and inspiring many artistic and cultural works, most notably the James Cameron blockbuster released in 1997.

• Titanic in facts and figures - BBC Bitesize

Image source, Getty Images

Hamish Harding, a 58-year-old British businessman and explorer, is reportedly onboard the missing submarine.

He studied Natural Sciences and Chemical Engineering at Cambridge University and later earned an Airline Transport Pilots Licence.

As a passenger on the fifth commercial flight of Blue Origin, Jeff Bezos's space firm, he was described by newspapers as a space tourist last year.

He's reportedly a billionaire and made much of his fortune dealing private jets.

Harding holds the Guinness World Record for traveling around the earth via North and South Poles.

Harding is now the chairman of Action Aviation, an international company which is dealing with sales and operations in the business aviation industry, based in Dubai, United Arab Emirates.

He first announced he was joining the team to see the Titanic wreck in June last year.

Here's a reminder of the short statement we got from OceanGate, the operator of the missing vessel.

• We are exploring and mobilising all options to bring the crew back safely

• Our entire focus is on the crew members in the submersible and their families

• We are deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to reestablish contact with the submersible

• We are working toward the safe return of the crew members

What might have happened to the missing vessel?published at 18:48 British Summer Time 19 June 2023

18:48 BST 19 June 2023

Pallab Ghosh
Science correspondent

Prof Alistair Greig from University College London is an expert on submarines. He has worked through a number of scenarios for where the missing submersible might be.

One is that it released a “drop weight” after an emergency, in order to bring it to the surface.

“If there was a power failure and or communication failure, this might have happened, and the submersible would then be bobbing about on the surface waiting to be found."

Another scenario, he says, is that the hull was compromised resulting in a leak. “Then the prognosis is not good.”

If it has gone down to the seabed and can’t get back up under its own power, the options - according to Prof Greig - are very limited.

“While the submersible might still be intact, if it is deeper than more than 200m (656ft) there are very few vessels that can get that deep, and certainly not divers.

“The vehicles designed for navy submarine rescue certainly can’t get down to anywhere near the depth of the Titanic.

"And even if they could, I very much doubt that they could attach to the hatch of the tourist submersible.”

A Titanic veteran diver says he was due to be on the missing submersible, and has been called to assist with search and rescue efforts.

Writing on a page called Titanic Book Club, external, David Concannon says: "As I posted last week I was supposed to be on this expedition and, indeed, on this dive, but I had to cancel to attend to another urgent client matter.

"Last night, I was called and asked to provide whatever assistance I could to ensure the safe return of everyone in the sub. Of course, I immediately agreed."

Concannon asks that people refrain from contacting him while "more important communications that need to be made to resolve this situation" continue.

Here's a recap of what we know so far about the missing submersible which was on a trip to the Titanic wreck site:

• A ship carrying the submersible set off from St John's, Newfoundland in Canada on Saturday, according to a social media post by British explorer Hamish Harding - thought to be on board
• It arrived near the location of the Titanic wreck in the Atlantic Ocean on Sunday morning, Harding wrote, where the submersible was then due to set off for an exploration dive
• It is unclear who was on board the vessel - but according to the operating company OceanGate, the vessel is designed to carry five people
• It has "life support" designed to last 96 hours for the whole crew
• Boston coast guard told the BBC it is leading the search and rescue operation

Toby Luckhurst
Washington DC

The BBC’s US partner CBS sent one of its reporters on a voyage with the same company last year to see the wreck of the Titanic.

David Pogue went on board the Titan submersible, operated by OceanGate, that is now the focus of a search and rescue effort in the North Atlantic.

In his report from last year,, external Pogue reads from what appears to be a waiver which describes the submersible as an “experimental” vessel, "that has not been approved or certified by any regulatory body, and could result in physical injury, disability, emotional trauma or death".

“Where do I sign?” he says to the camera with a smile.

OceanGate CEO Stockton Rush then gives him a tour of the submersible, where he reveals the vessel only has one button and is run using a video game controller.

When David Pogue questions him about the “jerry-rigged” nature of some components, Rush says that the company has worked with Nasa and Boeing to ensure the safety of the pressure vessel – the most important part of the sub.

“Everything else can fail. Your thrusters can go, your lights can go – you’re still going to be safe.”

When Pogue tried to descend in the sub, they had to cancel the journey only 37 feet under the surface, after a problem with some equipment on a platform linked to the sub.

A later attempt to reach the ocean floor on the sixth day of their voyage was also cancelled. Pogue did finally reach the wreck of the Titanic on the last day of the voyage.

Image source, CBS

Pallab Ghosh
Science correspondent, BBC News

According to OceanGate’s website, the five-person sub has system for monitoring the vessel’s hull in real time.

It has sensors and strain gauges to analyse the effects of changing pressure on the sub as it dives, in order to assess the integrity of the structure.

Critically, the company says: "This onboard health analysis monitoring system provides early warning detection for the pilot with enough time to arrest the descent and safely return to surface."

Expert Parks Stephenson, technical director on James Cameron's Titanic film, says the loss of communication with the missing submersible is a "highly unusual event".

Speaking on Radio 4's PM programme, Stephenson - who is not directly affiliated with the vessel's operating company OceanGate Expeditions - says each submersible has different characteristics.

But generally, he says, they take around two hours to reach the depth at which the Titanic lies - and will take around the same time to come back up.

It's not known who is on the vessel. But a British explorer, Hamish Harding, said yesterday that he was due to join the latest OceanGate expedition to the Titanic.

Harding wrote on Facebook, external and other social media platforms that a dive was being attempted on Sunday, after a crew had set off from the city of St John's, Newfoundland on Saturday.

He added that the team on the vessel includes "a couple of legendary explorers, some of which have done over 30 dives to the RMS Titanic since the 1980s".

He added that this trip was "likely to be the first and only manned mission to the Titanic" this year due to the harsh weather conditions.

• The Titan is a five-person submersible, to descend to depths of 4,000 metres, external
• Its dimensions are 670 cm x 280 cm x 250 cm
• It has "life support" of 96 hours for a crew of five
• It travels at three knots - that's around 3.5 miles per hour
• Aside from taking divers to the wreck of the Titanic, it's used for site survey and inspection, research and data collection, film and media production, and deep sea testing of hardware and software

• It's equipped with an integrated platform which the submarine launches from and returns to before and after each dive

Nomia Iqbal
BBC News, Washington

The operating company OceanGate Expeditions says it is getting extensive assistance from several government agencies and deep-sea companies as it tries to regain contact.

Athough the expedition set off from Canada, the Boston coast guard has told the BBC it is leading the search operation.

The vessel can carry up to five people - but we don’t know how many were on board.

The Titanic sits 3,800m (12,500ft) beneath the surface at the bottom of the Atlantic. It is about 600km (370 miles) off the coast of Newfoundland, Canada.

The passenger liner, which was the largest ship of its time, hit an iceberg on its maiden voyage from Southampton to New York in 1912. Of the 2,200 passengers and crew onboard, more than 1,500 died.

The Titanic has been extensively explored since the wreck was discovered in 1985.

It lies in two parts, with the bow and the stern separated by about 800m (2,600ft). A huge debris field surrounds the broken vessel.

OceanGate Expeditions, a private company that deploys submersibles for deep sea expeditions, recently posted on its social media feeds that one of its expeditions was "under way".

The company charges guests $250,000 (£195,270) for a place on its eight-day expedition to see the famous wreck.

It bills the trip on its carbon-fibre submersible as a "chance to step outside of everyday life and discover something truly extraordinary".

The submersible can seat five people, the company says, which usually includes a pilot, three paying guests, and what it calls one "content expert".

A full dive to the wreck, including the descent and ascent, reportedly takes eight hours.

Image source, .

The company operating the submersible which has gone missing says it is “exploring and mobilising all options” to bring the crew back safely.

“Our entire focus is on the crewmembers in the submersible and their families,” says OceanGate in a statement.

It says it has received “extensive assistance” from “several government agencies and deep sea companies” in its efforts to re-establish contact with the submersible.

“We are working toward the safe return of the crewmembers."