The lead engineer on the doomed Titan submersible said Monday that he “100%” felt pressure to get it in the water.

Tony Nissen — testifying as the first witness at a Coast Guard hearing into the sub’s deadly 2023 implosion at the site of the Titanic — described often clashing with company chief Stockton Rush over what he saw as his boss’s reckless, dangerous push to get the high-tech underwater vehicle up and running.

Nissen, asked by the investigators whether he felt heat to get the titanium and carbon-fiber vessel in the water as the lucrative linchpin of Rush’s OceanGate deep-sea-dive business, replied, “100%.”

Rush and four others — adventurer Hamish Harding, Titanic explorer Paul-Henri Nargeolet and multimillionaire Shahzada Dawood and his teen son Suleman Dawood — died when the craft imploded under enormous water pressure June 18, 2023.

Former OceanGate contractor Tym Catterson testified later Monday that the doomed date had looked like the “perfect diving day” — after lousy weather conditions had ruined previous attempted scheduled dives.

Since the catastrophe, widespread accounts of Rush’s alleged negligence, including involving safety shortcuts with the craft and his business, have surfaced.

Nissen recalled how he once refused to even step foot into the submersible several years ago.

“I’m not getting in it,” he said he told Rush at the time — explaining to Monday’s panel that he was worried about the level of expertise of the other staffers helping to operate it.

Nissen added that he stopped one of the sub’s trips to the Titanic in 2019, telling Rush that the craft was “not working like we thought it would.’’

He was fired later that year.

The testimony came as an eerie new photo also emerged of the Titan’s severed tail cone resting on the ocean floor after the tragedy.