Why there was still a huge search for the missing sub even though the Navy learned quickly that it probably imploded

• The US Navy detected a likely implosion around the time the Titan sub went missing.
• It hinted at disaster — but was inconclusive and officials still launched a massive search.

In an interview Thursday, "Titanic" director James Cameron blasted the four-day search for the Titan submersible as a "prolonged nightmarish charade."

It was, he argued, obviously from the get-go that the vessel was lost.

"For the sub's electronics to fail and its communication system to fail, and its tracking transponder to fail simultaneously – sub's gone," he told the BBC, citing conversations he had with experts soon after it vanished.

The rescue operation ended Thursday when a drone scouring the sea bed found remains of the vessel, which was carrying five people. The wreckage showed the signs of a catastrophic, unsurvivable implosion.

Cameron's remarks follow reports Thursday that the US Navy also had early reason to believe the sub was lost.

Data from its undersea-monitoring systems indicated the vessel imploded soon after setting off on Sunday, multiple reports said, information soon handed to US Coast Guard, which led the search.

So why did the Coast Guard still launch a vast search-and-rescue operation?

In a statement Thursday, the Navy said its data had not been definitive — leaving open the possibility that someone was still alive.

After analysis, "the decision was made to continue our mission as a search and rescue and make every effort to save the lives on board," the statement said.

Matthew Schanck, the director of MarSAR, a UK-based search-and-rescue consultancy, told Insider that this uncertainty, and the absence of physical evidence from the Titan, was crucial in the decision to search anyway.

"What they did was right. Now, if there was debris located very early on, on the surface let's say or something like that, we'd be having a different conversation. But until we had any physical evidence that there has been a catastrophic incident that we could say happened to the craft, we have to carry out a search and rescue operations," he said.

Schanck said that banging sounds detected during the search would have factored into the decision to keep searching even after several days had passed — even though the noises later found to probably be a false lead.

He said he was surprised the Navy did not go public sooner with its information. One reason might be to preserve the morale of those searching, he said.

"Dispatching crews searching for extended periods of time, searching wide expanses of the ocean, on the surface and underneath — it could be hard to keep people motivated and focused," Schanck said.

His comments echo those of Paul Zukunft, a retired Coast Guard admiral, who spoke to The Washington Post.

Zukunft said the Coast Guard would generally keep searching for survivors until it's "absolutely conclusive" that there are none.

"We're making every attempt that if there's a surface recovery; we are there," he said.

He compared the search for the Titan to the operation launched by the Coast Guard in 2015 for the El Faro, a cargo ship that went missing after getting caught in Hurricane Joaquin between Puerto Rico and Florida.

Despite pessimistic data indicating that the ship sank, Coast Guard crews still launched a search-and-rescue operation. It that case there were also no survivors, with 33 lives lost.

"For one or two people, we will literally spend millions of dollars in attempts to rescue these folks," he said.