[3] After testing with dives to its maximum intended depth in 2018 and 2019, the original composite hull of Titan developed fatigue damage and was replaced by 2021.

Since the discovery of the Titanic wreckage in 1985, limited tours of the wreck have been conducted, including the (Finnish-made) Russian Mir-class submersibles in the 1990s, which captured the footage for the opening scenes of the eponymous 1997 film.

[12] The forward end cap was fitted with an experimental 380 mm-diameter (15 in) acrylic window,[3][7] shaped as a modified conical frustum 180 mm (7 in) thick.

[13] Titan was equipped with a real-time acoustic monitoring system, which OceanGate claimed could detect the onset of buckling in the carbon fiber hull prior to catastrophic failure.

[16] OceanGate began developing a composite carbon fiber and titanium-hulled submersible in collaboration with the University of Washington's Applied Physics Laboratory (APL-UW) in 2013,[17] tentatively named Cyclops 2; the first titanium structural components were ordered in December 2016 from Titanium Fabrication Corp. (TiFab),[18] and OceanGate signed a contract with Spencer Composites in January 2017 for the carbon-composite cylinder.

[3] Spencer previously had built the composite pressure hull for the single-person DeepFlight Challenger for Steve Fossett to a design by Graham Hawkes.

[3][a] Spencer Composites was given challenging performance targets for Cyclops 2, which was meant to withstand 6,600 psi (46 MPa; 450 atm) working service pressure with a factor of safety of 2.25× for its intended maximum depth of 4,000 m (13,120 ft), and provided six weeks to complete the design.

[22] In an interview published in 2020 with Teledyne Marine, a subsea technology company, it was noted that many Oceangate employees were recent graduates.

[23] In 2015, when Rush visited DOER Marine seeking lessons learned from "Project Deep Search", DOER's president, Liz Taylor, specifically warned him against using carbon fiber; in 2023, she recounted that carbon fiber specifically has "been shown to not be very happy when it's being immersed first of all and then being hollow on the inside or just one atmosphere on the inside and then having the tremendous pressure of the ocean trying to push in on it, it's not the right material".

[24] The Marine Technology Society's committee on Manned Underwater Vehicles (now called Submarine Committee) drafted a private letter to Rush in March 2018, expressing concerns with the design of Titan and urging him to have the ship "classed" (certified by a ship classification society), partly because the marketing of the submersible, which stated it would meet or exceed the standards of DNV, was misleading because OceanGate had no intentions to have the vehicle tested by DNV.

In the post, OceanGate said "the vast majority of marine (and aviation) accidents are a result of operator error, not mechanical failure" and argued that classification focused solely on the physical state of the vessel and not its corporate actions, which it characterized as a "constant, committed effort and a focused corporate culture" of "maintaining high-level operational safety".

"[32] Screenwriter Mike Reiss confirmed the submersible lost contact on each of the four dives he had made with OceanGate and said "that seems to be just something baked into the system".

"[34] Rush had touted partnerships with NASA, Boeing, and UW to Pogue in 2022 in response to a question about the perceived "MacGyvery jerry-rigged-ness [sic]" improvisational design based on the use of off-the-shelf components.

[16][36] Documents leaked to Wired showed that partnerships with UW and Boeing dissolved and design recommendations and rigorous testing requirements were ignored.

Instead, Lochridge was told that OceanGate would rely on the real-time acoustic monitoring system, which he felt would not warn the crew of potential failure with sufficient time to safely abort the mission and evacuate.

In that meeting, he reiterated his concerns and added he would refuse to allow crewed testing without a hull scan; Lochridge was dismissed from his position as a result.

[6] Partway through that solo dive in December 2018, Rush used the vertical thrusters to overcome unexpected positive buoyancy when descending past 3,000 m (10,000 ft), which caused interference with the communication system, and he lost contact with the surface ship for approximately one hour.

[41] After the tests were completed in January 2020, the hull of Titan began showing signs of cyclic fatigue and the craft was de-rated to 3,000 m (9,800 ft).

[4] The Spencer-built composite cylindrical hull either was repaired or replaced by Electroimpact and Janicki Industries in 2020 or 2021, prior to the first trips to Titanic.

[5][44] According to Rush, the carbon fiber materials had belonged to Boeing, but OceanGate had purchased them at a significant discount because they were past their shelf-life.

Rush refused to construct new domes and other components from the failed submersible and instructed the engineers to salvage and reuse parts.

[13] In the first half of 2021 shallow water test dives were made in Washington state with prospective Titanic expedition passengers.

[48] In May 2021 television host Josh Gates and camera operator Brian Weed did a Titan test dive in Puget Sound.

During Gates and Weed's dive, communications were lost, the propulsion system encountered errors, and the computers on the submersible stopped working.

The passengers and crew would embark on the support ship from St. John's, Newfoundland, and sail southward for two days until they reached the location of the Titanic wreckage.

A passenger aboard this dive told the Vancouver Sun in 2023 "I really had a great time on that boat trip, even though we got stuck at the bottom.

[63] Reporter David Pogue and crew members from CBS News took part in OceanGate's fourth Titanic excursion of 2022, which took place between 9 and 17 July.

For the 2023 survey expedition, OceanGate secured MV Polar Prince as its support vessel and planned to begin excursions in May.

Because of the switch to Polar Prince, a platform known as the Launch and Recovery System (LARS), needed to be towed to the site, rather than carried on board.

[67][68] Several hours later, after the submersible failed to resurface at the expected time, the Polar Prince reported the situation to the United States Coast Guard.