The US Coast Guard has determined the implosion of OceanGate's Titan submersible that killed all five people on board was "preventable", citing the company's "critically flawed" safety practices.

A damning 335-page report from Coast Guard investigators states that OceanGate, the company that owned and operated the Titan, failed to follow maintenance and inspection protocols for the deep-sea vessel.

"There is a need for stronger oversight and clear options for operators who are exploring new concepts outside of the existing regulatory framework," Jason Neubauer, the chair of the Coast Guard Marine Board, said in a statement.

The Titan submersible disappeared in the Atlantic Ocean while descending to the wreckage of the Titanic on 18 June 2023.

OceanGate has extended its condolences to the families of the victims and stated that it "directed its resources fully toward cooperating with the Coast Guard's inquiry".

Here are five key takeaways from the two-year investigation.

The report condemns OceanGate's safety practices as fundamentally inadequate. It says the primary causal factor for the implosion was the firm's failure to follow "established engineering protocols" for safety and testing.

There were "glaring disparities between their written safety protocols and their actual practices", the report states.

"This marine casualty and the loss of five lives was preventable," said Jason Neubauer, the chairman of the Coast Guard Marine Board of Investigation that was charged with investigating the Titan disaster.

The company continued to use the Titan sub despite a series of previous incidents that compromised the craft without properly assessing its suitability, the investigation found.

The sub imploded 90 minutes into the dive after its carbon-fibre hull suffered a catastrophic loss of structural integrity, the investigation found.

The report says the crew died instantly, subjected to nearly 5,000 pounds per square inch of water pressure.

Carbon fibre has not been used for a deep diving sub before.

It is known to be unreliable under pressure, and its layers are known to come apart in a process called delamination.

The submersible did complete 13 dives to the Titanic in the two years preceding the tragedy. But the coastguard criticised the company's continued use of the submersible without checking its hull, after a number of safety issues were picked up its monitoring.

Rob McCallum, from EYOS expeditions, a specialist in deep water operations, who advised Oceangate between 2009 and 2016, told the BBC that carbon fibre is an unpredictable material.

"When you listen to the sounds of that hull under stress, and the cracking and the popping, that's the sign of damage in the hull, that means the hull is getting weaker," Mr McCallum said.

"So you can't expect to take a vehicle to the same depth every time knowing that it's weaker than the dive before, and expect it not to fail at some stage, It is a mathematical certainty that it will fail," he said. "The tragedy is, you don't know when it's going to fail."

The report also blames Stockton Rush, OceanGate's founder and the pilot of the Titan sub during its fatal voyage, for contributing to the disaster.

Rush "exhibited negligence that contributed to the deaths of four individuals" (apart from his own), investigators said.

Had he survived, investigators said they would have recommended referring him to the US Department of Justice for potential "criminal offences".

Coast Guard Marine Board of Investigation Chair Jason Neubauer told the BBC that the structure of the organisation was "deeply flawed".

"One of the biggest standouts that I think that any company could take away is, if your CEO, was also filling the role of safety officer, and lead engineer at the end, it's just too many," he said. "It's a consolidation of power that leads to no checks and balances."