OceanGate was warned of potential for ‘catastrophic’ problems with Titanic mission.

Leaders in the submersible craft industry were so worried about what they called the “experimental” approach of OceanGate, the company whose craft has gone missing, that they wrote a letter in 2018 warning of possible “catastrophic” problems with the submersible’s development and its planned mission to tour the Titanic wreckage.

The letter, obtained by The New York Times, was sent to OceanGate’s chief executive, Stockton Rush, by the Manned Underwater Vehicles committee of the Marine Technology Society, a 60-year-old trade group that aims to promote ocean technology and educate the public about it.

The signatories — more than three dozen people, including oceanographers, submersible company executives and deep-sea explorers — warned that they had “unanimous concern” about OceanGate’s development of the Titan submersible, the same craft that is now missing in the North Atlantic with five people on board.

The chairman of the committee, Will Kohnen, said in an interview Tuesday that the letter grew out of fears about what could happen if the company did not stick to established standards.

“The submersible industry had significant concerns over the strategy of building a deep sea expedition submersible without following existing classification safety guidelines,” Mr. Kohnen said.

The letter said that OceanGate’s marketing of the Titan had been “misleading,” because it claimed that the craft would meet or exceed the safety standards of a risk assessment agency known as DNV, yet the company had no plans to have the craft assessed by the agency.

The industry leaders said that OceanGate should test its prototypes under the watch of DNV or another accredited registrar.

“While this may demand additional time and expense,” the signatories wrote, “it is our unanimous view that this validation process by a third-party is a critical component in the safeguards that protect all submersible occupants.”

Mr. Kohnen said in the interview that Mr. Rush, OceanGate’s chief executive, called him after reading the letter and told him that industry regulations were stifling innovation. In a 2019 blog post titled “Why Isn’t Titan Classed?” the company made similar arguments.

OceanGate said in the post that because its Titan craft was so innovative, it could take years to get it certified by leading assessment agencies. “Bringing an outside entity up to speed on every innovation before it is put into real-world testing is anathema to rapid innovation,” the company wrote.

A spokesman for OceanGate declined to comment on the 2018 letter.

Another signatory of the industry group’s 2018 letter, Bart Kemper, said in an interview that he and other members were worried that the Titan had not followed standard certification procedures.

“This letter was basically asking them to please do what the other submarines do, especially the passenger ones,” said Mr. Kemper, a forensic engineer who works on submarine designs, citing Atlantis Submarines, a Canadian company that operates undersea tours, as an example.

Another signatory, Charles Kohnen, who is Will Kohnen’s brother, said the whole industry was worried about Titan. “We had concerns,” he said on Tuesday, “and we addressed them in the letter and we made sure that OceanGate received our concerns.”

More recently, OceanGate referenced some technical issues with the Titan in a court filing.

“On the first dive to the Titanic, the submersible encountered a battery issue and had to be manually attached to its lifting platform,” the company’s legal and operational adviser, David Concannon, wrote in 2022 in a filing in the U.S. District Court for the Eastern District of Virginia, which oversees matters having to do with the Titanic. The submersible sustained modest damage to its exterior, he wrote, leading OceanGate to cancel the mission so it could make repairs.

Still, Mr. Concannon wrote in the filing, 28 individuals had been able to visit the Titanic wreckage on the craft in 2022.

Mr. Concannon invited the federal judge who was hearing the case, Rebecca Beach Smith, to join the company for an expedition, according to a separate filing, something the judge seemed interested in doing.

“Perhaps, if another expedition occurs in the future, I will be able to do so,” the judge wrote in May, adding that after hearing for decades about the Titanic wreckage, “that opportunity would be quite informative and present a first ‘eyes on’ view of the wreck site by the Court.”

Kitty Bennett contributed research.