Sunday, surface contact was lost with a commercial submersible carrying tourists to view the wreck of the RMS Titanic. The Titan, an experimental craft run by OceanGate Expeditions, lost contact with its surface support ship about 1 hour and 45 minutes into its planned 12,500-foot descent carrying one crew member and four passengers who paid $250,000 each for the experience. Though the air supply on the submersible runs out Thursday, there was fresh hope that the crew might still be alive Wednesday when aircraft-deployed sonobuoys detected “banging” at regular intervals.

Aboard the Titan are Hamish Harding, a 58-year-old British businessman and explorer; British businessman Shahzada Dawood and his son, Suleman Dawood, 19; 77-year-old French explorer Paul-Henry Nargeolet, and OceanGate CEO Stockton Rush.

Praying for the safe return of :

Paul-Henry Nargeolet, 73
Stockton Rush, 61
Hamish Harding, 58
Shahzada Dawood, 48
Sulaiman Dawood, 19#Titanic #OceanGate pic.twitter.com/n0Yp8xZy2B

— MARISA (@MarisaSpice1985) June 21, 2023

Frank Owen, from the Submarine Institute of Australia, says he is confident – based on the information available – the sounds are coming from inside the vessel.

“If there was a 30-minute interval, it’s very unlikely to be anything but human related,” he told the BBC.
…
But Mr Owen says the noises “smack of advice” coming from the fifth man on board – 77-year-old Paul-Henry Nargeolet, a former French navy diver and renowned explorer.

“He would know the protocol for trying to alert searching forces… on the hour and the half hour you bang like hell for three minutes,” Mr Owen said.

Finding the Titan is only a small part of the problem. The deepest undersea rescue ever attempted was at 1575 feet, just over 10 percent of the depth of the lost submersible.

Adding to the difficulty is that the Titan does not have a conventional hatch system. Its hatch is bolted in place by a support team once the crew is inside. Because there appears to be life on board Titan, catastrophic hull failure and electrical fire can be ruled out.