The one-of-a-kind Titan submersible that imploded on its descent to the site of the Titanic this week, killing all five passengers, was made with experimental materials, including carbon fiber, which experts say has not been pressure-tested over time in such extreme depths. Since the fatal dive, the innovation behind the Titan and OceanGate Expeditions — the company that owned and operated the vessel for paid tours to the Titanic — has come under increased and intense scrutiny. Days after the Titan was reported missing, sparking a frantic search, the U.S. Coast Guard said Thursday that the 22-foot craft imploded, though...