OceanGate chief Stockton Rush, British adventurer Hamish Harding, father and son Shahzada and Suleman Dawood, and Frenchman Paul-Henri Nargeolet died when the Titan sub imploded after it began its descent last June.

Guillermo Sohnlein helped Mr Rush found the submersible company in 2009, but left OceanGate in 2013.

Speaking to a US Coast Guard public hearing investigating the doomed journey on Monday, Mr Sohnlein said he hopes the incident does not end interest in deep-sea exploring.

"This can't be the end of deep ocean exploration," he said. "This can't be the end of deep-diving submersibles, and I don't believe that it will be."

In defence of the company, he said OceanGate wanted to create a fleet of four or five deep-diving submersibles capable of carrying five people to 6,000m deep.

Mr Sohnlein said carbon fibre was used because the company wanted a lightweight and more affordable material, that did not need to be tethered to a specific mother ship.

He argued this was "not a novel idea" and said "people have looked at that before".

He denied that he or Mr Rush were "driven by tourism" or by the idea of exploring the Titanic - despite former operations director David Lochridge previously telling the hearing: "The whole idea behind the company was to make money".

Read more:
What happened to the Titan?

The Titan sub made its final dive to the Titanic wreckage on 18 June 2023, losing contact with the Polar Prince support ship around two hours later.

Rescuers rushed ships, planes, and other equipment to an area around 435 miles (700km) south of St John's, Newfoundland.

The search for the Titan attracted global attention, and the wreckage was eventually found on the ocean floor around 300m from the Titanic, according to officials.

Read more on Sky News:
The stories of those on the Titan submersible
Titan's last message: 'All good here'

The hearing in Charleston County, South Carolina, is expected to last until 27 September and has already heard how the Titan sub malfunctioned multiple times.

Fred Hagen, who had paid a fee to go on a dive in the Titan in 2021, said "all it could do was spin around in circles, making right turns" during an excursion.

OceanGate scientific director Steven Ross also told the panel a platform issue earlier in June 2023 caused passengers to "tumble about" and left one "hanging upside down". The sub imploded days later.