The submersible that imploded descending to the Titanic wreckage last year — instantly killing all five onboard — had malfunctioned just six days before its final doomed dive, a former OceanGate scientific director testified on Thursday.

Steven Ross, a marine scientist and crew member on the Titan’s 87th dive in 2023, said that a malfunction during that dive caused all five people onboard to “tumble about” and slam into the craft’s aft for at least an hour, CNN reported.

The dive, piloted by OceanGate’s late co-founder Stockton Rush, was aborted after an issue with the variable ballast tank — which controls the submersible’s buoyancy — caused the platform to invert 45 degrees shifting the back of the craft upwards.

Rush “crashed into the rear bulkhead, the rest of the passengers tumbled about, I ended up standing on the rear bulkhead, one passenger was hanging upside down, the other two managed to wedge themselves into the bow endcap,” Ross told the US Coast Guard Marine Board of Investigation.

Ross told the passengers what he believed had gone wrong and after taking a significant amount of time to try to fix the issue, he instead decided to ascend to the surface to address it.

The ex-employee added that he did not know whether the Titan’s hull was ever inspected for damage following the failed dive, which happened on June 12 — six days before the fatal plunge and about 460 miles from the Titanic site.

He admitted that he knew the Titan submersible had not been inspected by the United States Coast Guard in 2021, 2022 or 2023.

Ross also recalled two incidents during the 2022 Titanic expedition dives, including a loud “bang” heard while surfacing in Dive 80, according to CNN.

“There was a discussion about the bang with the crew, mission specialists and the scientists. The theory of the sound was that there was likely a shifting of the pressure hull in its metal cradle that when it popped back into place it could’ve made that loud noise,” Ross testified.

Then on Dive 81, Ross said there was a malfunction of the craft’s thrusters.

His confessions came to light during a US Coast Guard inquiry. A Coast Guard panel will hear two weeks’ worth of evidence into the Titan submersible disaster.

Since the catastrophe, widespread accounts of Rush’s alleged negligence, including taking safety shortcuts with the craft and his business, have come to light.

Rush and four others — adventurer Hamish Harding, Titanic explorer Paul-Henri Nargeolet and multimillionaire Shahzada Dawood and his teenage son Suleman Dawood — were killed when enormous water pressure destroyed the submersible on June 18, 2023.

Four days later, the mangled remains of Titan were discovered on the ocean floor about 330 yards off the bow of the Titanic, Coast Guard officials said. 

Tony Nissen, OceanGate’s lead engineer on the fatal mission, said on Monday he often clashed with Rush when his boss recklessly pressured his team to get the high-tech underwater vehicle up and running.

On Tuesday, OceanGate’s former director of marine operations David Lochridge detailed the “appalling” faults with the original model of the doomed Titan submersible.

“The whole idea of the company was to make money. There was very little in the way of science,” Lochridge said.

The USCG will continue its hearings on Friday and into next week.