re: Titanic tourist submarine goes missing

Titan (4000 meters)
Design and construction
OceanGate began developing a composite carbon fiber and titanium-hulled submersible in collaboration with the University of Washington's (UW) Applied Physics Lab (APL) in 2013,[16] 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.
Spencer previously had built the composite pressure hull for the single-person DeepFlight Challenger for Steve Fossett to a design by Graham Hawkes.
[19] After Fossett died, DeepFlight Challenger was acquired by Richard Branson's Virgin Oceanic, which had announced plans to conduct a series of five dives to the deepest points of the oceans; DeepFlight refused to endorse the plan, as the craft had been designed to dive only once. Adam Wright, the president of DeepFlight, stated in 2014
"The problem is the strength of the [DeepFlight Challenger] does decrease after each dive. It is strongest on the first dive."[20] Spencer Composites was given challenging performance specifications 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 (13,000 ft).[19] In March 2018, Cyclops 2 was renamed to Titan[21] and by 2019, OceanGate stated that they had begun development of the successor Cyclops 3 and 4 submersibles.

safety of 2.25×

not much of a margin of safety