A submarine expert and engineer has presented a chilling vision of the final moments of the doomed Titan submersible’s crew, claiming that those onboard would have been fully aware of what was happening in the minute leading up to its catastrophic implosion beneath the waves of the North Atlantic.

Spanish submarine expert José Luis Martín claims that an electrical failure left the crew unable to control the sub and sent it plummeting “like an arrow” toward the sea floor with those inside piled on top of each at the nose of the craft, looking out of its porthole into the inky depths.

Martín told Spanish media outlet NIUS that it would have been “like a horror movie”.

He said he believe that the trouble began when Titan reached a depth of 1700 metres when it suffered an electrical failure that saw it lose propulsion.

With those onboard crowded at the nose for a view of their journey the craft quickly became unbalanced, he claimed.

“At that moment, the submarine falls headlong like an arrow towards the bottom of the sea, without any possibility of manoeuvering with the damaged control and safety elements,” the former engineer on a tourist submarine said.

“The pilot could not activate the emergency lever that abruptly released the lead ballasts and that the company pompously announced in one of its advertising videos,” Martín claimed, saying that the safety measure was inadequate.

He said those onboard suffered through between 48 and 71 seconds of the fall before the craft failed.

“Imagine the horror, the fear and the agony. It must have been like a horror movie,” he told NIUS.

“In that period of time, they are realising everything. And what’s more, in complete darkness. It’s difficult to get an idea of what they experienced in those moments. After those 48 seconds, or one minute, the implosion and instantaneous sudden death occur,” he said.

He said that the rapid descent put pressure on the experimental craft until it imploded “like when you prick a balloon”.

British adventurer Hamish Harding and father and son Shahzada and Suleman Dawood were killed on board the vessel near the wreckage of the Titanic, alongside OceanGate Expeditions’ chief executive, Stockton Rush, and French national Paul-Henri Nargeolet.

Large pieces of debris from Titan were transported to shore last month by the Horizon Arctic ship, where it was seen being unloaded by a crane.

An underwater robot carried to the site by the Horizon Arctic had dived to the ocean floor to search for the Titan during the multi-day, international search.

Those conducting the official investigation believe the Titan imploded as it made its descent into deep North Atlantic waters on June 18. The Coast Guard said last month that human remains have likely been recovered from the wreckage of the submersible and are being examined by medical officials in the US.

Remotely operated vehicles, known as ROVs, were used to retrieve the debris from the ocean floor about 3810 metres underwater and a ship later brought pieces of the wreckage to a port in Canada to be examined. The debris was found roughly 488m from the Titanic.

The US Coast Guard has convened a Marine Board of Investigation, its highest level of investigation, into the implosion, and plans to hold a public hearing in the future.

- Additional reporting, AP