U.S. Navy acoustic sensors detected the likely implosion of the Titan submersible hours after the vessel began its fatal voyage on Sunday, U.S. Navy officials said on Thursday, a revelation that means the sprawling search for the vessel came as senior officials already had some indication the Titan was destroyed.

Debris from the submersible, operated by the private firm OceanGate, was discovered Thursday on the seabed of the Atlantic Ocean about 1,600 feet from the Titanic, the doomed ocean liner that the Titan’s passengers had set out to explore. Coast Guard Rear Adm. John Mauger said the debris was discovered underwater by a remotely operated vehicle, four days after it set out from Newfoundland.

A senior Navy official said in a statement Thursday evening that the service conducted an analysis of acoustic data “and detected an anomaly consistent with an implosion or explosion” in the general vicinity of where the Titan was operating when it stopped communicating.

“While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission,” the statement said. “This information was considered with the compilation of additional acoustic data provided by other partners and the decision was made to continue our mission as a search and rescue and make every effort to save the lives on board.”

Another Navy official, speaking on condition of anonymity because of the sensitivity of the situation, said that the service does not typically share such information publicly until the search for survivors ends. The information gathered, this official said, is a “data point.”

The story was first reported by the Wall Street Journal.

Paul Zukunft, a retired Coast Guard admiral, said that until it’s “absolutely conclusive” that no one has survived a disaster, the service always will continue searching for survivors.

“We’re making every attempt that if there’s a surface recovery; we are there,” he said. “Nothing would be worse in cold water, and now there’s no one on the surface or in the air to locate these folks.”

Zukunft, who led the Coast Guard as commandant from 2014 to 2018, drew a parallel with a search the Coast Guard carried out after the 2015 sinking of the container ship El Faro, which got caught in Hurricane Joaquin while traveling from Florida to Puerto Rico and sunk. Navy acoustic sensors detected an implosion in that sinking, he said, but the U.S. government continued searching for several days in case there were any survivors. Thirty-three people died.

In other cases, Zukunft said, the Coast Guard has launched searches in the Pacific after fishermen in Micronesia do not return home. They have been known to survive weeks lost at sea on small boats, relying on fish they catch and rainwater.

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

The acoustic detection was one significant piece of information, but the search had to continue to exhaust all possibilities, said Mark Cancian, a senior adviser with the Center for Strategic and International Studies.

“They suspected what happened but couldn’t be sure,” he said. “What you’re looking at is just lines on a graph. And if you try to convince people you weren’t doing a search because the lines on a graph indicated an implosion, that wouldn’t be acceptable to many.”

The United States has used a network of devices to detect undersea noises for decades. The fact that the Titan’s implosion was detected this way isn’t surprising, Cancian said. “I would be surprised if they hadn’t heard it.”

The U.S. military has recovered vessels and downed aircraft at depths similar to the Titan, but Zukunft doubted that will occur in this case. It would be a “very costly undertaking” to do so, he said, and there was no recorder on the Titan to learn more about the disaster.

“The Titan,” he said, “now has five members interred on the debris field.”