Large parts of the Titan tourist submersible have been recovered from the ocean after a fatal implosion that instantly killed three Brits on board.
British adventurer Hamish Harding and father and son Shahzada and Suleman Dawood were killed inside the deep-sea vessel, alongside OceanGate Expeditions' chief executive, Stockton Rush, and French national Paul-Henri Nargeolet.
They were set to explore the famous Titanic wreckage located 12,500 feet beneath the ocean, but now presumed human remains have been discovered, the US Coast Guard revealed on Wednesday night.
Photos have since emerged of large chunks of debris being retrieved and transported to shore in St John's, Newfoundland, Canada, sparking questions about how such big pieces could survive an implosion of such magnitude.
The pieces included a large, white section of curved metal appearing to show the outer casing of the 21-ft Titan sub. Another piece showed cables, onboard computers and other mechanical parts.
A large circular part of the Titan, which appeared to be the dome-shaped front section, was also found.
But it has left many questioning how such large pieces of the sub were discovered when the explorers on board experienced a 'catastrophic implosion'.
Experts previously told NBC News that the water pressure on the sub would have been the equivalent of the 10,000-ton, wrought-iron Eiffel Tower.
The force of the implosion, it was said, would have been so strong that the craft's carbon-fibre hull would have just 'suddenly vanished', vaporising and killing all inside before they knew anything was wrong.
So why are there any remains to recover in the first place?
A coastguard source from St John's, where the ill-fated adventurers set off on June 17, told the Mirror the debris will now be pieced back together to help with ongoing investigations - including the UK Marine Accident Investigation Branch that has been brought in to probe the tourist deaths.
And this could be made easier due to the size of the craft's remains, according to an expert.
The submersible's construction included at least one titanium end cap, a titanium ring and a carbon fibre cylinder.
OceanGate had been previously warned by ex-staff members of the safety of the submersible after it was revealed its carbon fibre hull, which housed the five passengers, was its "Achilles heel" - because the material is not considered suitable for deep dives.
Tom Maddox, CEO at Underwater Investigators, said investigators were expecting the Titan to have been blown to pieces.
"Many of us suspected that, in the case of this catastrophic failure, this implosion, that a lot of the parts would be disintegrated, particularly the non-titanium parts, which, of course, would make the investigation a lot harder to do," he told DailyMail.com.
Although finding larger remains means investigators will have "more pieces of the puzzle to put together".
"They'll put it back as best they can," he said.
"I don't think there's a rulebook for this, you know, there's no manual, this is something new.
"And they're going to have to kind of write the book as they go along, would be my thought, but they'll use their past experiences and their knowledge to do that."
Meanwhile, Arun Bansil, university professor of physics at Northeastern, has explained a basic overview of the physics involved in the violent crash before explaining the reason why we are seeing such large pieces of debris.
"In an explosion, the force acts outwards, but in an implosion, the force acts inwards. When a submersible is deep in the ocean it experiences the force on its surface due to water pressure," he told Northeastern Global News.
"When this force becomes larger than the force hull can withstand, the vessel implodes violently.
"The key is the design of the hull that protects the vessel against the large external water pressure that is trying to crush the hull."
Professor Bansil says that most of the existing technology is based on steel, titanium and aluminium, with the performance of these materials under extreme stress being well understood.
He added: "However, the Titan's hull had an experimental design.
"It used mostly carbon fibres, which have the advantage of being lighter than titanium or steel, so Titan could have more space for passengers.
"Properties of carbon fibres for deep sea applications are, however, not that well understood. It can crack and break suddenly.
"Titan had previously gone for deep sea dives a few times, which would have contributed to the fatigue of the hull to make the hull more prone to catastrophic failure."
Speaking with the Mirror, the expert explained why we have seen large parts of the vessel remain intact.
"Although it seems counterintuitive, large objects do not normally split apart into smithereens in an implosion or explosion," Prof Bansil said.
"For example, a pressure cooker usually explodes with the top blown off but the body remains intact. The initial failure of Titan would have occurred at its weakest links such as defects in the hull.
"Once a crack opens, however, large pieces of the hull will no longer experience very violent forces and remain more or less intact."
At this stage, officials are not sure how soon into the dive the vessel imploded.
The Titan submersible lost contact with tour operator OceanGate Expeditions an hour and 45 minutes into the two-hour descent to the wreckage, with the vessel reported missing eight hours after communication was lost.
Stockton Rush, CEO of OceanGate, previously explained in a haunting interview that "as you're descending, you've got your depth and altitude… that's pretty critical. When you get close to the bottom, you have to be ready to drop some weight so you don't go crashing into it, or thrust..
The billionaire, who has officially been declared deceased, continued: "So getting that notification 200 metres above the bottom is pretty critical. And then when we use our laser scanning system, we need correction data for through water speed currents and the light to keep the errors down, and that’s it, that’s the element of adding [coms] on the sub."
Pelagic Research Services – whose remote operating vehicle (ROV) discovered the debris fields – said on Wednesday its team is 'still on mission'.
In a statement, Captain Jason Neubauer, Chair of the Marine Board of Investigation said: "I am grateful for the coordinated international and interagency support to recover and preserve this vital evidence at extreme offshore distances and depths.
"The evidence will provide investigators from several international jurisdictions with critical insights into the cause of this tragedy.
"There is still a substantial amount of work to be done to understand the factors that led to the catastrophic loss of the Titan and help ensure a similar tragedy does not occur again."
In a statement last week, OceanGate said it was "an extremely sad time for our employees who are exhausted and grieving deeply over this loss".
