If the submersible now missing in the icy seas of the North Atlantic is still intact, the fate of the five men inside may rest on one crew member - a highly experienced mariner from France called Paul-Henri Nargeolet.
Nargeolet knows the sea - the 77-year-old spent two decades in the French Navy, serving as a deep-sea diver, an underwater mine clearer and a submarine pilot.
He also knows the Titanic - perhaps better than anyone else on Earth.
He has participated in some 35 dives to the resting place of the doomed passenger liner and runs a company which owns the salvage rights and displays artefacts at special exhibitions.
This famous mariner has many friends and admirers, among them a seafarer called Jose Paulo Viera da Silva.
This Portuguese captain, who has piloted oil tankers and merchant ships for over 30 years, is well acquainted with Nargeolet - and he respects his knowledge and his nerve.
"You can see that he is very experienced. When he [conducts] missions at sea he doesn't have problems and I believe that he will be one of the solutions to this situation."
According to the Portuguese, Nargeolet will draw on lessons learned from a life both at and under the sea.
"Do you think he could find a solution to this?" I asked.
"I think he will help, of course. I think he can [work with] the other people on board so they can have a good expectation to come to the surface."
"You believe that, even now, with oxygen supplies running out on [the submersible] Titan?" I asked.
"Yes, I [will] believe this to the last moment. It would be a pity if we lose that man."
Da Silva captained the supply boat which took Nargeolet and his crew to the site of the Titanic in 2010.