Questions About Infamous Lost Sub Resurface as Navy Releases New Documents Tied to Decades-Old Mystery

Memorial ceremony for the 50th anniversary of the loss of the U.S. Navy submarine USS Thresher (SSN 593)
Capt. Thomas Ishee, commander of Submarine Squadron (SUBRON) 11, delivers remarks during a memorial service for the 50th anniversary of the loss of the U.S. Navy submarine USS Thresher (SSN 593). The ceremony honored the 129 men lost on Thresher, which sank off the coast of Cape Cod April 10, 1963, during sea trials. (Kyle Carlstrom/U.S. Navy)

Almost 60 years have gone by since the Thresher, then the Navy's newest nuclear-powered submarine, plummeted to the bottom of the sea during a deep-dive test. Now, recently declassified documents are adding to the confusion and debate around the service's deadliest submarine loss.

Documents released by the Navy in July describe a series of events aboard the submarine Seawolf -- one of the ships that was searching the area after communications were lost with the Thresher on April 10, 1963. The Seawolf heard a series of sounds that have led to speculation that the Thresher's crew may have been alive longer than previously thought.

However, experts on the submarine's sinking dismiss the possibility.

"You could see the men on the Seawolf hoping against hope thinking the sound might be some survivors and recording them," Chris Drew, author of a book that investigated the incident, "Blind Man's Bluff," and a former military journalist, explained. "There's a lot of sounds in the ocean."

The Thresher sank with 129 men aboard. In its wake, the Navy created a submarine safety program, SUBSAFE, to ensure that future submarine hulls would stay watertight and that they can recover from unanticipated flooding.

The new documents show that the Seawolf arrived in the area the Thresher was believed to have sunk on the morning of April 11, 1963, just over 24 hours after the sub disappeared. The declassified log shows that, over a series of four dives, the submarine reported hearing various pings and sounds it thought might be the missing Thresher.

At one point, the Seawolf broadcast: "We hear your underwater telephone. If you will send 5 dashes we will have positive Identification -- send 5 dashes." There is no report of five dashes being received, but the Seawolf continued to try to get a fix on the source of the pings.

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About halfway through its search, the submarine reported a "total of 37 pings heard counted."

The Seawolf also reported sailors "may hear very weak voice" over their underwater receivers. They asked for a repeat of the message, but one was never received.

On one dive, the Seawolf reported metal on metal banging heard on sonar. In between requests to "bang 5 times on hull," the submarine reported hearing more bangs, but a later entry conceded "he does not give us number asked for."

The log also notes that what the sailors were hearing "could be sounds from [destroyers] in vicinity."

Crushed by Ocean Pressure

Unbeknownst to the Seawolf at the time, every major investigation has concluded that, by the time it began its first dive search, the Thresher had already been crushed by the ocean pressure after sinking to 2,400 feet -- 400 feet past what its hull could take.

Norman Polmar, an author and naval analyst who wrote the book "Death of the USS Thresher," discounts the possibility that what the Seawolf heard was surviving sailors in a still intact Thresher.

"I don't believe it," Polmar flatly told in an interview.

Polmar points to the recordings from the Navy's underwater Sound Surveillance System, or SOSUS, as key evidence in forming his opinion.

"We know from the SOSUS tapes ... that the submarine imploded," he said. "If it imploded, that means they collapsed inward. Everyone died instantly -- there was no clanging on the metal."

Drew also pointed out that it's highly unlikely the submarine could still float, or have positive buoyancy.

"[The Thresher] couldn't have just been maintaining positive buoyancy and nobody can find them," he told in an interview.

Drew noted that both the Seawolf and the surface ships that were part of the search-and-rescue efforts all had sonar systems.

"If a massive submarine is sitting at 1,000- to 2,000-feet deep for a day, don't you think sonar would have picked it up?" he asked. "It doesn't make any sense."

Unsurvivable Waters

Drew, who co-authored Robert Ballard's recently released memoir "Into the Deep: A Memoir From the Man Who Found Titanic," said the famed undersea archaeologist, who surveyed the Thresher wreck shortly before he located the Titanic, confirmed that the submarine sank in unsurvivable deep waters.

"[Ballard] said it was far enough from the continental shelf that it just went straight down and then once they got a little past crush depth ... that was it," Drew said.

Both Drew and Polmar noted that there could be any number of explanations for what the Seawolf crew heard and reported in 1963.

"You can be 500 miles from something and, because [of] underwater currents, the temperature gradients and other things, hear something that's 500 miles away," Polmar said.

He was quick to note, though, that "it might have been the other ships and submarines that were in the area."

USS Thresher (SSN 593) at sea on July 24, 1961.

In fact, one entry in the Seawolf report notes several times that other Navy ships in the area were making noises that made it difficult to listen for sounds from the Thresher.

The newly released details also draw attention to the fact that disagreement remains on what initially caused the Thresher to lose power and sink.

The Navy's official position is that an inadequate welding technique caused a pipe to fail on the submarine.

Retired Vice Adm. Ron Thunman, who commanded the Thresher's sister sub, the Plunger, summed up the Navy position in an oral history interview in 2012.

"A pipe ruptured, and the spray grounded the electrical systems. ... It caused the reactor to [shut down]," Thunman said.

In addition, the Navy later learned that if you try to blow a submarine's ballast tanks from that deep a depth, as the Thresher did, the air piping would cause ice to form and prevent the sub from surfacing.

"So, [the Thresher's commander] had no propulsion; he had no blow system, and they lost the ship," he said.

Thunman went on to become deputy chief of naval operations, and he was the officer who ordered Ballard to survey the Thresher wreck in the 1980s as part of an agreement that also gave the oceanographer funding to find the site of the Titanic.

Electrical Failure?

However, Polmar, along with Bruce Rule, wrote an analysis in Navy Times in 2013, on the 50th anniversary of Thresher's loss, arguing for a different cause for the power failure.

Rule was the analyst who studied the recordings related to the loss of the Thresher and testified before the Navy's court of inquiry on the incident. He went on to serve as the lead acoustic analyst in the Office of Naval Intelligence for 42 years, retiring in 1992.

Rule and Polmar argued that acoustic evidence indicated that an electrical failure, not a leak or flooding, caused the reactor's coolant pumps to shut down.

Polmar, who once spoke with the Thresher's first commander, Dean Axene, said the naval officer told him that one of the Thresher's final messages to ships on the surface supports his theory.

Shortly before contact was lost, the Thresher sent a message that read: "Experiencing minor difficulty, have positive up-angle, attempting to blow."

Polmar told that Axene said "the only thing that he could think of at test depth, 1,300 feet, that he would describe as a minor difficulty, was a reactor shutdown because that happened periodically, not regularly, but every now and then, and there was a procedure for restarting it."

Rule, in an open letter to Navy leadership in 2013, wrote that the message was "evidence those difficulties did not involve flooding with the catastrophic effects such flooding is known to create at great depth."

Those still passionate about answering all the questions about the Thresher, including former naval officers and family members of the crew, hope to get more answers as the Navy releases more documents.

Ultimately, neither Polmar nor Drew feel that the revelations of the sounds heard by the Seawolf change their understanding of the submarine's sinking.

Drew said the new details are "very intriguing, alluring" but ultimately a footnote in the larger Thresher saga.

Polmar said he "wouldn't even give it that much credit."

In 2019, a memorial to the Thresher’s crew was unveiled at Arlington National Cemetery.

"Their sacrifice will now rightfully be memorialized at our nation's most hallowed grounds beside tributes here to generations of fallen heroes," Sen. Jeanne Shaheen, D-N.H., said at the time.

-- Konstantin Toropin can be reached at Follow him on Twitter @ktoropin.

Related: Navy Declassifies 300 Pages of Probe into 1963 USS Thresher Disaster

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