A US Coast Guard investigative board concluded on Tuesday that the "inadequate design" of the Titan submersible was a primary contributing factor in its implosion in 2023 that left five people dead.

The Titan was on a tourist expedition to the wreckage of the Titanic – a British passenger liner that sank in 1912, killing at least 1,500 on board – when it lost contact with its support vessel during descent. Its remains were found four days later, littering the seabed about 1,600 feet (488 metres) from the bow of the Titanic wreck.

The implosion was preventable, the chair of the US Coast Guard Marine Board of Investigation, Jason Neubauer, said as a 300-page report was released following a two-year probe.

"There is a need for stronger oversight and clear options for operators who are exploring new concepts outside of the existing regulatory framework," he said in a statement.

A media spokesperson at OceanGate, the US-based company that managed the tourist submersible and suspended all operations after the incident, was not immediately available for comment.

The board determined that the primary contributing factors were OceanGate’s "inadequate design, certification, maintenance and inspection process for the Titan."

It also cited "a toxic workplace culture at OceanGate", an inadequate regulatory framework for submersibles and other novel vessels, and an ineffective whistle-blower process.

The report added, "For several years preceding the incident, OceanGate leveraged intimidation tactics, allowances for scientific operations, and the company’s favourable reputation to evade regulatory scrutiny."

The board found that OceanGate failed to investigate and address known hull anomalies following its 2022 Titanic expedition. It said data from Titan’s real-time monitoring system should have been analysed and acted on during that expedition.

It also criticised OceanGate for failing to properly store the Titan before the 2023 Titanic expedition.