A series of mistakes preceded the Titan submersible's doomed mission to visit the Titanic wreckage, which culminated this week in the deaths of everybody on board.
The five passengers on board the Titan died in a catastrophic explosion, both the US Coast Guard and its operators OceanGate said Thursday, citing debris found on the ocean floor.
Now, questions are being asked about why safety concerns about the design and operation of the vessel appear to have been ignored or dismissed.
While it's unclear what caused the implosion, experts have pointed to red flags about Titan's safety that were evident before the trip. Here are five:
The Titan was made up of two titanium domes joined together by a five-inch-thick cylinder of carbon fiber.
This was unconventional choice for a deep-sea submersible, which would usually have a hull made of stronger materials like steel or titanium, per The Telegraph.
The advantage of using carbon fiber is that it is a lot lighter and cheaper.
The disadvantage is that it has "no strength in compression" film director and deep-dive expert James Cameron told The New York Times. Cameron has dived dozens of times to the Titanic shipwreck and has designed vessels for his own explorations, per the Times.
OceanGate had been warned about the safety risks associated with the use of the material, according to a 2018 court filing.
Per the filing, former OceanGate employee David Lochridge raised concerns about "pressure cycling," whereby invisible flaws in the hull could lead to larger tears after being subjected to repeated pressure changes.
OceanGate's CEO, Stockton Rush, said in an interview two years ago that he knew he had "broken some rules" by foregoing conventional materials.
"I think I've broken them with logic and good engineering behind me. Carbon fiber and titanium? There's a rule you don't do that," he said in a 2021 interview with Mexican YouTuber Alan Estrada. "Well, I did."
A December 2018 statement from OceanGate said the Titan had completed a 4,000 meter dive which "completely validates OceanGate's innovative engineering and the construction of Titan's carbon fiber and titanium hull"
OceanGate touted its development of an advanced acoustic monitoring system. The technology was designed to warn of a failure in the hull in time to do something about it.
But in his 2018 analysis, Lochridge warned that the detection system was effectively useless - it would only provide "milliseconds" of warning before a catastrophic implosion, according to the court filing.
OceanGate declined to follow his recommendation of "non-destructive testing" on the hull to ensure it was "a solid and safe product for the safety of the passengers and crew," Lochridge's lawsuit said.
The firm told Lochridge that the Titan's hull was too thick to scan for weak spots and adhesion issues, as previously reported by Insider.
It's unclear if the pilot's concerns were ever addressed or whether OceanGate later ran the tests he recommended. OceanGate declined to comment on the 2018 letter when approached by the New York Times.
It's possible that the ship never passed strict industry-standard safety testing - and indeed in 2019 it argued that it did not need to.
David Pogue, a journalist who boarded the Titan in 2022, said he signed a waiver stating: "This experimental vessel has not been approved or certified by any regulatory body."
It is possible that the ship was certified since then, though no evidence has emerged that it was.
In his court filings, Lochridge reported finding that the vessel's front viewport was only certified to a depth of about 4,200 feet (1,300 meters) far less than the depth of the Titanic.
"The paying passengers would not be aware, and would not be informed, of this experimental design," Lochridge's lawyers wrote.
The company's approach to certification was raised by the professional trade group the Marine Technology Society in a 2018 letter.
The Society flagged that the company's website said the vessel design would meet or exceed a certification called DNV-GL, a gold standard industry certification from Norwegian foundation Det Norske Verita, CBS news reported.
But it didn't appear the company had sought to follow those rules, the Marine Technology Society noted in its letter.
The listing on the company's website could be "misleading to the public and breaches an industry-wide professional code of conduct we all endeavor to uphold," per the Society's letter.
"Their plan of not following classification guidelines was considered very risky," Will Kohnen, the chairman of the Manned Underwater Vehicles committee of the Marine Technology Society, said in an interview on Tuesday, per The New York Times.
Kohned said Rush later called him to say that industry standards were stifling innovation, per The Times.
In a 2019 blog, the company defended its decision to not class the vessel, saying accidents in marine and aviation settings mostly result from "operator error, not mechanical failure."
"As a result, simply focusing on classing the vessel does not address the operational risks," the company said.
Lochridge did not fare well after raising safety concerns about the submersible.
A day after filing his safety report, he was summoned to a meeting with Rush and the company's human resources, per the lawsuit. During the meeting, Lochridge was fired and removed from the building.
Lochridge claimed he was discharged in retaliation for being a whistleblower and sued the company that year, per TechCrunch.
OceanGate claimed Lochridge had shared confidential information with external actors and characterized his report as false, accusing him of fraud in the lawsuit, the report said.
Lochridge was not the only one to leave the company over concerns about safety. Rob McCallum, an explorer and former consultant for OceanGate, left the company in 2009 partly over concerns its CEO was over-promising and rushing production, Insider previously reported.
Speaking to Insider recently, McCallum said he was familiar with the equipment used in the Titan submersible and did not think it was safe for use.
This isn't the company's first time dealing with issues with its submersibles. According to court documents obtained by The New York Times, a 2021 trip on the Titan was interrupted after battery issues led to the ship having to be manually attached to its lifting platform.
Pogue, the journalist who went on the Titan in 2022, also reported that the vessel got lost for several hours while he was on the mother ship.
"They could still send short texts to the sub, but did not know where it was," Pogue said. "It was quiet and very tense, and they shut off the ship's internet to prevent us from tweeting."
When reached by Insider for comment on Wednesday, Pogue said OceanGate told passengers that it shut off the WiFi to free up bandwidth in case the situation developed into an emergency.
Pogue also revealed the craft lacked an emergency location transmitter (ELT), which would emit signals that allow rescuers to find it.
OceanGate did not immediately respond to a request by Insider for comment on each of these claims.