Veteran explorer Josh Gates, who hosts a TV series investigating myths and legends around the world, revealed on Twitter Wednesday that the missing OceanGate sub "did not perform well" when he went on a dive aboard the vessel himself.

The 21-foot deep-sea submersible vanished Sunday morning during an attempt to reach the shipwrecked Titanic, which sank in the Atlantic on the way to New York from England in 1912.

Gates, who hosts "Expedition Unknown" on Discovery, had gone with Stockton Rush, the OceanGate CEO who is now among five missing along with the Titan sub, on a test dive before the vehicle's first visit to the Titanic site.

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Gates wrote that he missed a chance to see the wreck himself due to fears about OceanGate's actual capabilities – concerns echoed in a 2018 lawsuit brought by a former employee who claimed he'd been wrongfully fired for blowing the whistle on the vehicle's maximum range himself.

"To those asking, #Titan did not perform well on my dive," Gates wrote. "Ultimately, I walked away from a huge opportunity to film Titanic due to my safety concerns w/ the @OceanGate platform."

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In 2018, former OceanGate employee David Lochridge refused to greenlight manned tests of the submersible, according to the lawsuit. The Washington-based company later sued Lochridge for disclosing confidential information, and he filed a counterclaim.

The lawsuit was settled out of court, and Gates made a cryptic comment that there were more flaws with the vessel than publicly known.

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"There's more to the history and design of Titan that has not been made public – much of it concerning," Gates wrote.

The "Expedition Unknown" host did not immediately respond to a request for comment from Fox News Digital.

Like Hamish Harding, who is also aboard the missing sub, Gates is a member of the Explorers Club – a research-minded international society of adventurers, many of them very wealthy, including the billionaire Amazon founder Jeff Bezos.

The missing Titan sub is estimated to have less than a day's worth of breathable air left.

Authorities said at a Wednesday news briefing the crew had some food and water, but it was unclear how much. 

However, authorities said they have picked up repeated sounds of banging in the search area and are still treating the mission as a search-and-rescue effort.

The missing crew members are OceanGate CEO Stockton Rush; British businessman Hamish Harding, father-and-son Shahzada and Suleman Dawood, who are members of one of Pakistan’s wealthiest families; and Paul-Henry Nargeolet, a former French navy officer and leading Titanic expert.