Any investigation that follows will undoubtedly try to work out exactly what happened to the sub - but how will experts do this?

Ryan Ramsey, former submarine captain in the Royal Navy, says the authorities involved will be gathering every piece of debris they can find, before bringing them to the surface to look for the breaks in the carbon fibre structure.

"There is no black box, so you are not going to be able to track the last movements of the vessel itself," he says.

The big question investigators will be trying to answer is whether the cause was a structural failure.

Read more here.

Safety measures onboard the OceanGate craft have been under intense scrutiny since the Titan sub went missing.

William Kohnen, who chairs the Manned Underwater Vehicles Committee in Los Angeles, is another from the industry to criticise the lack of regulations around the sub.

Kohnen, who previously authored a letter to OceanGate raising concerns about the safety of its craft, tells BBC Breakfast the disaster was "clearly preventable".

He lauds the success of the underwater submersible industry, which he says has not seen any major disasters since the 1960s.

This kind of submersible with tourists on board "would not be allowed" in US, British or Canadian waters without it being certified, he adds.

What is an implosion?published at 09:47 British Summer Time 23 June 2023

09:47 BST 23 June 2023

Pallab Ghosh
Science correspondent

According to Rear Admiral John Auger, the pattern of the debris is consistent with “a catastrophic implosion”.

But what is an implosion and how is it different from an explosion?

Essentially an implosion is a sudden collapse of the vessel, in this case likely due to the enormous water pressure on the Titan. An explosion would have been an outward force coming from within the craft.

The submersible was so deep in the sea that the amount of water on it would have been equivalent to the weight of the Eiffel Tower, tens of thousands of tonnes.

The people inside are kept safe by the hull.

But if there were a rupture to the structure, the pressure outside would compress the vessel and disintegrate its carbon fibre body.

Image source, Dirty Dozen Productions

The family of Hamish Harding remembers the British billionaire explorer as "a dedicated father" who "lived his life for his family, his business and for the next adventure".

"Hamish Harding was a loving husband to his wife and a dedicated father to his two sons, whom he loved deeply," his family said in a statement released by his company Action Aviation.

"He will leave a gap in our lives that can never be filled."

The 58-year-old ran Action Aviation, a Dubai-based private jet dealership. He had completed several exploration feats, including visiting the South Pole multiple times and flying into space in 2022.

Dik Barton, the first British man to dive to the wreck of the Titanic, describes Titan passenger Paul-Henry Nargeolet as an "extraordinary individual".

Speaking to BBC Breakfast, he pays tribute to his friend and French explorer, reminiscing on the dives they had done together.

But he says: "What we were doing was a professional, underwater exploration using purpose-built submersibles which are designed to work at those depths."

Barton also calls into question the design and the maintenance of the OceanGate craft, saying "there were many red flags flying here".

With the news all five men aboard the OceanGate Titan submersible have died following a likely catastrophic implosion, many will be asking the same question - what happens next?

Rear Admiral John Mauger of the US Coast Guard, who has been leading the search operation this week, could not confirm whether the bodies of the five victims would be able to be located and recovered.

The coastguard said teams will continue to investigate the site of the debris field, with several vessels, medical personnel and technicians in the area.

The focus will also switch to a likely inquiry over what actually happened - whether it can be categorically confirmed that an implosion caused the deaths of those on board and, if so, when and why it happened.

You can read more about this here.

Here's a look back on how Stockton Rush - the pilot of the Titan submersible and founder of the company that created it - described his love for the ocean in an interview for a BBC documentary.

"Every time I dive, I see something I've never seen before, that no humans probably [have] ever seen before," he said.

Rush wanted OceanGate to be a business that "[got] people excited about the ocean, explore the ocean, discover what was out there".

"People are so enthralled with the Titanic," he said, describing it as a "must-do dive".

The 61-year-old was one of the five killed on board the Titan submersible.

This graphic from the US Coast Guard shows the search patterns rescue teams had been covering while looking for the Titan earlier in the week.

On Thursday, a remotely operated vehicle discovered five major parts of the submersible.

Some of that debris was located on the ocean floor, 480m (1600 ft) from the bow of the Titanic wreck. The exact location has not been disclosed.

Image source, US Coast Guard, DVIDS, 21 June

In our post below, Sohnlein was reacting to comments by Hollywood director James Cameron, who had earlier joined the chorus of experts raising concerns about the safety of the Titan in an interview with the BBC.

Cameron said that the deep submergence community had previously raised concerns about OceanGate's vehicle, and had even written to the company saying, in his words, "you are going on a path to catastrophe".

He compared the Titan's tragedy to the loss of the Titanic itself and her crew in 1912, calling it a "terrible irony".

"We now have another wreck that is based on unfortunately the same principles of not heeding warnings," he said. "OceanGate were warned."

Cameron said that he "felt in my bones" that the sub had been lost soon after it went missing.

"I immediately got on the phone to some of my contacts in the deep submersible community. Within about an hour I had the following facts. They were on descent. They were at 3500 metres, heading for the bottom at 3800 metres," he said.

"You can't lose comms and navigation together without an extreme catastrophic event."

Guillermo Söhnlein, a co-founder of OceanGate, has rejected some of the criticisms directed at the company over safety and certification.

Söhnlein left the company 10 years ago but still retains a minority stake.

Speaking on BBC Radio 4's Today programme, he said those commenting on the Titan's safety, including film director James Cameron, were not fully informed.

"People keep equating certification with safety and are ignoring the 14 years of development of the Titan sub," he says.

"Any expert who weighs in on this, including Mr Cameron, will also admit that they were not there for the design of the sub, for the engineering of the sub, for the building of the sub and certainly not for the rigorous test programme the sub went through."

Söhnlein said it had been a "tragic loss for the ocean exploration community" but anyone who operates in the deep ocean "knows the risk of operating under such pressure and that at any given moment... you run the risk of this kind of implosion".

He added that he thought technology and innovation can outpace regulation and developers are in a better position to understand the risks and best minimise them.

Image source, Reuters

The families and friends of those lost on the Titan sub have been paying tribute to their loved ones.

Relatives of the renowned French diver Paul-Henri Nargeolet said he will be remembered as "one of the greatest deep-sea explorers in modern history". The 77-year-old was known as a world-leading Titanic expert who had completed more than 35 dives to the ocean liner wreck.

The Dawood family, who are grieving after the loss of Shahzada Dawood, 48, and his son Suleman, 19, said: "The family remains overwhelmed with the love and support that it has received and is grateful to the those who showcased the best in humanity.”

The family of British billionaire explorer Hamish Harding have called him "a dedicated father" and said: "If we can take any small consolation from this tragedy, it's that we lost him doing what he loved."

Stockton Rush was the chief executive of OceanGate, the firm that operates the Titanic voyages on the lost submersible.

The company said it was a tragic time, adding: "These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world's oceans."

Questions are being raised abound the safety of deep-sea submersibles and how they are regulated following the Titan tragedy, after it emerged that the vessel imploded under water.

OceanGate's Titan may not have needed to pass the same tests other vessels are subject to because it was operating in international waters where deep sea exploration is "unregulated", said Dr Simon Boxall, a senior lecturer in oceanography at the University of Southampton.

In the UK, any vessel - a boat, submersible or ROV (remotely operated vehicle) - must pass "incredibly stringent safety checks" before it is allowed to enter the water, he told BBC Breakfast.

"The problem is that this particular vessel, this particular submersible, didn't come under anyone's jurisdiction."

Image source, PELAGIC RESEARCH SERVICES

The company that made the remote- operating vehicle (ROV) that found the Titan's debris said their efforts had been focused on a rescue.

They had been working with the Canadian ship Deep Energy, which had the lifting capacity to bring the the Titan back to the surface.

“We have been just one part of an incredible and overwhelming maritime rescue response,” said the Massachusetts-based Pelagic Research Services.

“It’s a difficult loss, and our hearts go out to the families and friends of all those affected by this tragedy."

We still don't know for sure when the Titan sub imploded.

The US Coast Guard said the sonar buoys it had deployed this week had not picked up any loud or violent noises indicating an implosion.

But the position of the debris field - relatively close to the shipwreck - and the timing of the Titan's last communication with its parent ship seemed to suggest the failure occurred near the end of its descent on Sunday.

It's emerged now the US Navy also heard an implosion sound on Sunday but search efforts continued because it wasn't definitive.

Sounds picked-up earlier this week by research vessels have been disregarded as probably coming from other vessels.

"There doesn't appear to be any relation between the noises and the location of the debris field on the sea floor," said Rear Admiral John Mauger, who led the search.

The Titan began its two-hour descent to the Titanic wreck on Sunday. It lost communications with its surface vessel about an hour and 45 minutes into the dive.

Image source, Reuters

Emily McGarvey
Live reporter

Welcome to our coverage of the Titan submersible as our team in London takes over from our colleagues in Singapore and Sydney.

So far we've found out that major fragments of the Titan were located on the ocean floor yesterday, 480m (1600ft) from the bow of the Titanic wreck.

We've also heard that the US Navy detected a sound consistent with an implosion just hours after the Titan began its dive on Sunday.

Tributes have been pouring in for the five men killed in the implosion, with St John's community - where the expedition began - speaking to the BBC about the loss.

The find completes a five-day search across nations which spanned more than 20,000 sq km of ocean.

I'm here with my colleagues Gem O'Reilly, Anna Boyd and Ali Abbas Ahmadi to bring you the latest.

"I was profoundly hoping all day and all day yesterday that they would be able to save them."Members of the St John's community - the capital of Newfoundland where the expedition to the Titanic began - spoke to the BBC about the loss of the Titan.

The deeper you go, the more water you have above you pressing down on you.

It’s unclear what caused the Titan sub to implode, but experts say it could have been caused by a small weakening of its outer hull.

The pressure experienced at sea level is referred to as “one atmosphere” or approximately 14.6lb (6.6kg) of pressure per square inch.

That pressure is increased by an entire atmosphere for every 10 metres of water depth. Therefore, at a depth of 3,000 metres – approximately where the sub was when it came apart – the pressure is about 300 times the pressure at the surface.

The Titanic wreck sits in the so-called Midnight Zone, known officially as the bathypelagic zone, which sits at a depth of between 1,000 and 4,000 metres. The temperature down there is approximately 4C (39F) and the pressure is at least 100 times that at sea level.

The very few animals that have adapted to live down there have evolved to survive the extreme pressure, darkness and cold - and die quickly when brought to the surface.

Those on board would have died instantly in an implosion, a former US Navy physician has said.

Dale Mole said the passengers wouldn't have even known there was a problem.

He added that being stuck inside the vessel would have been a far worse alternative.

"You can just imagine what it would have been like... it's cold, your oxygen is running out.

"If we can't have them back, this is the best possible scenario," he said.

The US Navy detected “an acoustic anomaly consistent with an implosion” just hours after the Titan began its dive on Sunday.

The information was immediately shared with the US Coast Guard, which used it to narrow the scope of its search, an official told CBS News.

But it's not clear why this information was not made public earlier.

It's believed the implosion sound was picked by the Navy's secretive long-range sonar listening system which has its origins in the Cold War.

The Sound Surveillance System was created in the 1950s to listen for Soviet submarines in the remote depths of the Atlantic Ocean.

Precise details of current operations are classified, but a US Navy website describes them as performing “detection, localisation and tracking of submarines and the collection of acoustic and hydrographic information.”

The White House has issued a statement on the five men killed on board the Titan submersible.

“Our hearts go out to the families and loved ones of those who lost their lives on the Titan,” it said in a statement.

“They have been through a harrowing ordeal over the past few days, and we are keeping them in our thoughts and prayers.”

It also thanked those involved in the vast multinational search for the sub.