The Ultra-Secret Underwater Spy System That Might Have Heard the Titan Implode

WASHINGTON—There are government secrets, and then there are government secrets about underwater spying.

Of all the categories of national secrets the U.S. government keeps, few have been as tightly guarded as how the military uses sophisticated acoustic technology to keep an ear on what its adversaries are doing thousands of feet below the sea. 

Driving the push for such capabilities are decades of Cold-War brinkmanship and fears about Soviet submarines that could launch nuclear weapons. Today’s tensions with China have provided a reminder of the systems’ importance: The People’s Liberation Army Navy sails a fleet of dozens of submarines, including six that can carry ballistic missiles. 

“Anything involving the nuclear triad is supersecret,” said Brynn Tannehill, a senior technical analyst at RAND, referring to the strategic concept of nuclear weapons deployed from land, sea and air. “Anything involving U.S. sensor capabilities is supersecret.” 

One such system—it couldn’t be determined which—heard what officials thought could be the implosion of the Titan submersible just hours after the vehicle began its voyage Sunday to the wreck of the Titanic. The U.S. Navy reported its findings to the Coast Guard commander on site, U.S. officials said. While the Navy couldn’t say definitively the sound came from the Titan, the discovery helped to narrow the scope of the search for the lost craft before its debris was discovered Thursday.

U.S. efforts to develop underwater-surveillance capacities trace back more than a century. Sonar, which uses sound waves to detect and locate objects, was used in World War I by the British and others to detect submarines. During World War II, the U.S. developed long-range sonar systems to detect German U-boats in the Atlantic. 

At the dawn of the Cold War, the U.S. began work on what would become the Sound Surveillance System, or SOSUS. Developed to detect Soviet nuclear submarines, SOSUS relied on a network of listening devices called hydrophones fixed to the sea floor. Even the program’s name was kept classified until after the collapse of the Soviet Union. The location and capabilities of the hydrophones remain secret today.

“The danger of nuclear war became a central fact of modern life and a furious arms race began,” centered on submarines and acoustic-detection systems, according to a history of submarine acoustic detection written by the Navy. 

“On the seas the admitted goal of Soviet admirals was to achieve naval supremacy, to use the navy as a key element of Soviet global strategy,” the history said.

SOSUS has been used to find wrecked vessels before, including the USS Thresher, a nuclear-powered submarine that sank in 1963 during diving tests off Cape Cod, Mass., killing all 129 people aboard.

The system remains in use today, and it likely detected the noises made by the implosion of the Titan, said Tannehill, the Rand analyst. But other detection methods might also have aided the search. Whatever happened, it might be a long time before the government discloses its secrets. 

“As soon as you start talking about anti-submarine warfare systems and boats in the North Atlantic, you immediately hit top-secret clearance,” Tannehill said. 

“So if the Navy doesn’t seem particularly forthcoming, it can’t be particularly forthcoming without presidential authority to declassify anything they say,” she said.

Write to Dustin Volz at [email protected]