USS Thresher (SSN-593)



USS Thresher (SSN-593) underway, 30 April 1961

Ordered: 15 January 1958
Builder: Portsmouth Naval Shipyard
Laid down: 28 May 1958
Launched: 9 July 1960
Commissioned: 3 August 1961
Motto: Vis Tacita (Silent Strength)
Fate: Lost with all hands during deep diving tests, 10 April 1963; 129 died.

The second USS Thresher (SSN-593) was the lead boat of her class of nuclear-powered attack submarines in the United States Navy. She was the U.S. Navy's second submarine to be named after the thresher shark.

On 10 April 1963, Thresher sank during deep-diving tests about 350 km (220 mi) east of Boston, Massachusetts, killing all 129 crew and shipyard personnel aboard. It is the second-deadliest submarine incident on record, after the loss of the French submarine Surcouf, in which 130 crew died. Her loss was a watershed for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as SUBSAFE. The first nuclear submarine lost at sea, Thresher was also the third of four submarines lost with more than 100 people aboard, the others being the Argonaut, lost with 102 aboard in World War II, the Surcouf, and the Kursk, which sank with 118 aboard in 2000.

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Sinking

On 9 April 1963, Thresher, commanded by Lieutenant Commander John Wesley Harvey, left from Kittery, Maine, at 8:00 a.m. and met with the submarine rescue ship Skylark at 11:00 a.m. to begin her initial post-overhaul dive trials, in an area some 190 nmi (350 km) east of Cape Cod, Massachusetts. That afternoon, Thresher conducted an initial trim-dive test, surfaced, and then performed a second dive to half of her 1,300-foot (400-meter) test depth. Before she entered the yard in late 1962, the Thresher had been to her test depth about 40 times. She remained submerged overnight and re-established underwater communications with Skylark at 6:30 a.m. on 10 April to commence deep-dive trials. Following standard practice, Thresher slowly dove deeper as she traveled in circles under Skylark – to remain within communications distance – pausing every 100 ft (30 m) of depth to check the integrity of all systems. As Thresher neared her test depth, Skylark received garbled communications over underwater telephone indicating " ... minor difficulties, have positive up-angle, attempting to blow", and then a final, even more garbled message that included the number "900". When Skylark received no further communication, surface observers gradually realized a problem had occurred.

By mid-afternoon, 15 Navy ships were en route to the search area. At 6:30 p.m., the commander of Submarine Force Atlantic sent word to Portsmouth Naval Shipyard to begin notifying the crew's family members, starting with Commander Harvey's wife Irene, that Thresher was missing.

Chief of Naval Operations Admiral George W. Anderson Jr. went before the press corps at the Pentagon to announce that the submarine was lost with all hands. President John F. Kennedy ordered all flags to be flown at half staff from 12 to 15 April in honor of the 129 lost submariners and shipyard personnel.

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Cause

Deep-sea photography, recovered artifacts, and an evaluation of Thresher's design and operational history permitted a court of inquiry to conclude that the submarine had probably suffered the failure of a salt-water piping system joint that relied heavily on silver brazing instead of welding. Earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require repair. But on 30 November 1960, nearly three years prior to the accident, USS Barbel suffered such a silver-braze joint failure near test depth while on an exercise, flooding the engine room with an estimated 18 tons of water in the 3 minutes it took to surface under power and with blown tanks. This incident was followed months later by more silver-braze failures aboard the ballistic missile submarine USS Abraham Lincoln during trials. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, causing a shutdown {"scram"} of the reactor, which in turn caused loss of propulsion.

The inability to blow the ballast tanks was later attributed to excessive moisture in the submarine's high-pressure air flasks, moisture that froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dockside tests on Thresher's sister sub, Tinosa. During a test to simulate blowing ballast at or near test depth, ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air dryers were later retrofitted to the high-pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly. Submarines typically rely on speed and deck angle (angle of attack) rather than deballasting to surface; they are propelled at an angle toward the surface. Ballast tanks were almost never blown at depth, as doing so could cause the submarine to rocket to the surface out of control. Normal procedure was to drive the submarine to periscope depth, raise the periscope to verify that the area was clear, and then blow the tanks and surface the submarine.

Subsequent study of SOSUS (sound surveillance system) data from the time of the incident has given rise to doubts as to whether flooding preceded the reactor scram, as no impact sounds of the high pressure water in the compartments of the submarine could be detected on instrument recordings from SOSUS at the time. Such flooding would have caused a significant sonic event, and no evidence of such may be found in the recorded data.

At the time, reactor-plant operating procedures did not allow for a rapid reactor restart following a scram, or even the ability to use steam remaining in the secondary system to propel the submarine to the surface. After a scram, standard procedure was to isolate the main steam system, cutting off the flow of steam to the turbines providing propulsion and electricity. This was done to prevent an overly rapid cool-down of the reactor. Thresher's reactor control officer, Lieutenant Raymond McCoole, was not on the boat during the fatal dive; his trainee, Jim Henry, fresh from nuclear power school, probably followed standard operating procedures and gave the order to isolate the steam system after the scram, even though Thresher was at or slightly below its maximum depth. Once closed, the large steam system isolation valves could not be reopened quickly. Reflecting on the situation in later life, McCoole was sure that he would have delayed shutting the valves, thus allowing the boat to "answer bells" and drive itself to the surface, despite the flooding in the engineering spaces. Admiral Rickover noted that the procedures were for normal operating conditions, and not intended to restrict necessary actions in an emergency involving the safety of the ship. After the accident Rickover further reduced plant restart times, which had already been gradually improving with new technology and operating experience, in addition to limiting factors that could cause a shut down.

In a dockside simulation of flooding in the engine room, held before Thresher sailed, the watch in charge took 20 minutes to isolate a simulated leak in the auxiliary seawater system. At test depth with the reactor shut down, Thresher would not have had 20 minutes to recover. Even after isolating a short circuit in the reactor controls, it would have taken nearly 10 minutes to restart the plant.

It was believed at the time that Thresher likely imploded at a depth of 1,300–2,000 ft (400–610 m), though 2013 acoustic analysis concluded implosion occurred at 2,400 ft (730 m).

The U.S. Navy has periodically monitored the environmental conditions of the site since the sinking and has reported the results in an annual public report on environmental monitoring for U.S. naval nuclear-powered craft. These reports provide results of the environmental sampling of sediment, water, and marine life, which is performed to ascertain whether Thresher's nuclear reactor has had a significant effect on the deep-ocean environment. The reports also explain the methodology for conducting deep-sea monitoring from both surface vessels and submersibles. The monitoring data confirm that there has been no significant effect on the environment. Nuclear fuel in the submarine remains intact.[citation needed]

Information declassified in the 2008 National Geographic Documentary Titanic: Ballard's Secret Mission, shows that USNR Commander (Dr.) Robert Ballard, the oceanographer credited with locating the wreck of RMS Titanic, was sent by the Navy on a mission under cover of the search for Titanic to map and collect visual data on the Thresher and Scorpion wrecks. Ballard had approached the Navy in 1982 for funding to find Titanic with his new deep-diving robot submersible. The Navy conditionally granted him the funds if the submarine wrecks were surveyed before Titanic. Ballard's robotic survey showed that the depth at which Thresher had sunk caused implosion and total destruction; the only recoverable piece was a foot of marled pipe. His 1985 search for Scorpion revealed a large debris field "as though it had been put through a shredding machine." His obligation to inspect the wrecks completed, and with the radioactive threat from both established as small, Ballard then searched for Titanic. Financial limitations allowed him 12 days to search, and the debris-field search technique he had used for the two submarines was applied to locate Titanic.

Almost all records of the court of inquiry remain unavailable to the public. In 1998, the Navy began declassifying them, but decided in 2012 that it would not release them to the public. In February 2020, in response to a FOIA lawsuit by military historian James Bryant, a federal court ordered the Navy to begin releasing documents by May 2020.

On May 22, 2020, the Navy stated in a court-mandated status report that due to the ongoing COVID-19 pandemic, the Navy's Undersea Warfare Division (OPNAV N97) had placed the records review on hold as N97 staff were limited to supporting mission-essential tasks supporting undersea forces and operations only. However, the Navy stated that they "will return to the review and process of Plaintiff’s FOIA request once the office is able to expand beyond mission-essential capabilities." Following the release of the July 18, 2020 court-mandated report the Navy stated that they had identified and approved additional resources and reservists to begin processing the documents in August. The Navy began a rolling release of the records on September 23, 2020.

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Memorials

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Other

• On 12 April 1963, President John F. Kennedy issued Executive Order 11104 paying tribute to the crew of Thresher by ordering all national flags to half-staff.
• Five folk music groups or artists have produced songs memorializing Thresher; "Ballad Of The Thresher" by The Kingston Trio, "The Thresher Disaster" by Tom Paxton; "The Thresher" by Phil Ochs on his 1964 album All the News That's Fit to Sing, "The Thresher" by Pete Seeger, and "Thresher" by Shovels & Rope.
• The Fear-Makers, an episode in the 1964 season of the television series Voyage to the Bottom of the Sea is inspired by the loss of the USS Thresher. Anthony Wilson, a writer for the series, was fascinated by the loss of the USS Thresher, and he wrote a teleplay for the series. In Wilson's teleplay, the submarine, the Seaview, searches for a missing submarine, the Polidor.

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