All five people aboard the Titan died when it was crushed near the world's most famous shipwreck, U.S. Coast Guard Rear Adm. John Mauger said Thursday, bringing an end to a massive multinational search that began Sunday when the vessel lost contact with its mother ship in the unforgiving North Atlantic.

The Titan, owned and operated by OceanGate Expeditions, first began taking people to the Titanic in 2021. It was touted for a roomier cylinder-shaped cabin made of a carbon-fiber—a departure from the sphere-shaped cabins made of titanium used by most submersibles.

The sphere is "the perfect shape," because water pressure is exerted equally on all areas, said Chris Roman, a professor at the University of Rhode Island's Graduate School of Oceanography. Roman had not been on the Titan but has made several deep dives in Alvin, a submersible operated by the Woods Hole Oceanographic Institute in Massachusetts.

The 22-foot long (6.7-meter long), 23,000-pound (10,432-kilogram) Titan's larger internal volume—while still cramped with a maximum of five seated people—meant it was subjected to more external pressure.

Elongating the cabin space in a submersible increases pressure loads in the midsections, which increases fatigue and delamination loads, said Jasper Graham-Jones, an associate professor of mechanical and marine engineering at the University of Plymouth in the United Kingdom.

Fatigue, he said, is like bending a wire back and forth until it breaks. Delamination, he said, is like splitting wood down the grain, which is easier than chopping across the grain.