Washington DC - The US Coast Guard investigation outlined a litany of issues with operator OceanGate's conduct, as well as design flaws in its Titan submersible, that contributed to a "preventable tragedy" in which all five passengers were killed.

The 335-page report said "OceanGate's failure to follow established engineering protocols for safety, testing, and maintenance of their submersible, was the primary causal factor" for the implosion.

It also accused the company of "intimidation tactics...to evade regulatory scrutiny."

OceanGate had a "toxic workplace environment which used firings of senior staff members and the looming threat of being fired to dissuade employees and contractors from expressing safety concerns," the report said.

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OceanGate chief executive Stockton Rush was joined on the doomed expedition by British explorer Hamish Harding, French deep-sea explorer Paul-Henri Nargeolet, Pakistani-British tycoon Shahzada Dawood, and his son Suleman.

Seats on the submersible cost $250,000 per person.

Communications were lost with the SUV-sized submersible about an hour and 45 minutes into its dive on June 18, 2023, kicking off a dramatic search that briefly captivated the world.