At a press briefing on Tuesday afternoon, US Coast Guard Capt. Jamie Frederick assessed that the vessel had just about 40 hours of breathing air left.

The hunt for the missing vessel has encompassed the American and Canadian Coast Guards, commercial vessels, and airplanes.

Mr. Rush, the company’s founder; Hamish Harding, a British businessman and explorer; Shahzada Dawood and his son, Suleman, from one of Pakistan’s wealthiest families; and Paul-Henri Nargeolet, a French maritime expert who has been on more than 35 dives to the Titanic wreck site.