Thresher was created to find and destroy Soviet submarines. It was the fastest and quietest submarine of her day. She also had the Navy’s most advanced weapons system, including anti-submarine missile launchers (SUBROC) and passive and active sonar that could detect vessels at unprecedented range.
America’s First Modern Submarine
Thresher was the lead ship of a new class of fast-attack submarines and was the culmination of more than a decade of scientific and engineering research to develop a submarine hunter-killer platform to address the threat that Soviet submarines posed. Hunter-killer submarines were conceived long before a functioning ballistic missile submarine (SSB or SSBN) was ever constructed in 1949. But when the Soviets began to field SSBs (Zulu V, Golf I, and Golf II), conventional submarines armed with a few nuclear ballistic missiles, at the end of the 1950s, the need for a hunter-killer submarine was of vital importance.
Thresher and her sister boats were designed for diving deeper, running more silently, and detecting what cannot be seen.[1] Thresher was built to be quieter than previous submarines by installing rubber washers between metal parts and fasteners to reduce the radiant noise of the submarine from metal-on-metal contact. The shape of Thresher was also an evolution of a tear-shaped hull that was more hydrodynamic than those of World War II and the Korean era. This hull form allowed the submarine to sail more efficiently submerged than on the surface. The tear shape and improved hull plates made from HY-80 (which can withstand 80,000 psi) allowed the Thresher class to dive deeper than their World War II counterparts.[2] Thresher-class submarines could operate at depths around 1,300 feet. In contrast, most World War II submarines operated at around 400 feet, and improved Korean War Era submarines could go as deep as 650 feet.
Victory in a submarine-on-submarine engagement depended on hearing and targeting the enemy before they could do the same to you. The Thresher-class was equipped with a new passive SONAR (AN/BQQ-2), which could hear the sounds of submarines at great distances. The SONAR array was fitted into the submarine’s bow, forcing the torpedo room to shift to amidships. With the increased sensitivity to detecting enemy submarines, operating more quietly, and diving deeper, the new class of submarines was provided with a litany of weapons. The boat’s weapons included the conventional Mark 37 Torpedo (anti-shipping/anti-submarine), the nuclear-tipped Mark 45 ASTOR (anti-submarine torpedo), and the new SUBROC (submarine-launched rocket), a weapon launched from the torpedo tubes to the surface to take a flight to its target. The Thresher class could also deploy seamines from their torpedo tubes. Thresher was shorter than her World War II counterparts (278.5 feet) and roomier at 31 feet/8 inches (as opposed to the older submarine’s 16-17 feet diameter pressure hull).
Portsmouth Naval Shipyard
The story of U.S.S. Thresher began at the Portsmouth Naval Shipyard in Kittery, Maine, when her keel was laid down in 1958. She was completed and launched four years later. After being outfitted, Thresher made a preliminary dive to a safe 600 feet in July 1961 and then was commissioned in August 1961 and placed under the command of Commander Dean L. Axene, a World War II submarine officer. After commissioning, Thresher underwent extensive testing for nearly a full year. Testing results exceeded the expectations of the designers and engineers. Thresher’s testing included sound tests in the Bahamas to determine how effectively the silencing measures suppressed radiant sound vibrations from her machinery and reactors. She passed her sound tests with flying colors.
Thresher returned to New London, Connecticut, and prepared for another shakedown cruise to Puerto Rico with the USS Cavalla (SS 244) to conduct anti-submarine exercises. This cruise foreshadowed things to come.
During the exercise, the Thresher put into San Juan, Puerto Rico, which did not have the port facilities to provide external power to the submarine. According to the standing operating procedure, the reactor was shut down, and the auxiliary diesel engine aboard the submarine provided everyday power until it broke down. The loss of the diesel engine would make it difficult to restart the reactor, but all was not lost at that point. The Thresher had a large storage battery but would not power the submarine for long.
Restarting a nuclear reactor requires a lot of time and electricity; without the diesel engine, the boat would need all the electricity in the battery. This meant they had to turn off ventilation and internal lighting to conserve as much electricity as possible to restart the reactor. In the process of getting the reactor started the temperature in the room climbed to an unbearable 140 degrees Fahrenheit. As the battery was dying, the mechanics were still working on the diesel engine, and the reactor still had not come online. Cavalla came alongside Thresher and connected her diesel engines to electrical cables to provide power to Thresher. The help from Cavalla allowed Thresher to get her reactor and life support systems back on.
For the rest of 1961 and into 1962, Thresher conducted additional tests, including test firing of dummy SUBROCs, testing her new SONAR system, and shock testing by dropping depth charges in and around the submarine. Though she only suffered minor damage overall, it was enough vibration to shake loose some of the boat’s silencing measures.
Returning to the Bahamas, additional stealth tests found that Thresher made much more noise than typical metallic groans under pressure. In July 1962, Thresher returned to Portsmouth Naval Shipyard for an extensive (worrisome) overhaul. Initially, the work was scheduled for completion by January 1963. Still, rework was delayed until April 1963 due to the prioritization of the construction of nuclear ballistic submarines on the shipyard’s slipways.
During this prolonged overhaul, most of the crew, both officers and enlisted men, were reassigned. Lieutenant Commander John Harvey relieved Commander Axene as Commanding Officer. Harvey was a young officer who had graduated from the Naval Academy in 1950 and had been part of the Nuclear Submarine program since its inception. He was a highly qualified officer with training and qualification aboard three nuclear-powered submarines. He had served as the nuclear reactor officer aboard USS Nautilus (SSN 571), the engineering officer aboard USS Tullibee (SSN 597), and later the executive officer (XO) aboard USS Seadragon (SSN 584).
Of the eleven officers assigned to Thresher in March 1963, five were qualified submarine officers, and three were qualified in nuclear power plants. To qualify in submarines, an officer or an enlisted sailor is tested in each of the sections and jobs of a submarine to the degree they can fill in in case of an emergency. Passing all these tests earns a sailor their “dolphin,” a device worn by a qualified submariner. Only three of the crew’s eleven officers had spent significant time aboard Thresher. This unfamiliarity with submarines (generally) and Thresher (specifically) was also reflected in the enlisted crew. Thresher’s green crew was one of the contributing factors in this tragedy.
In a reversal of priorities, the Deputy Commander, Submarine Force, U.S. Atlantic Fleet ordered that more fast-attack submarines be readied for sea. Shipyard Portsmouth prioritized the overhaul of the Thresher. The initial work was completed in March, and LCdr Harvey planned a “fast cruise” where they would simulate being underway. Harvey identified five hundred deficiencies, but only about 200 required corrections to prepare the vessel for sea. The shipyard quickly made the repairs, and the “fast cruise” resumed on 31 March. The simulation demonstrated how unprepared the crew was for sailing. For example, a flooding drill took the crew over 20 minutes to isolate the problem.
Prelude to Tragedy
Thresher returned to sea on 9 April 1963, leaving Portsmouth Naval Shipyard for a two-day cruise to perform a number of dives — including a dive to her test depth of 1,300 feet. Thresher was in the company of the USS Skylark (ASR 20).[3] Thresher set sail from Portsmouth with a crew of 129 — twelve officers, 96 enlisted crew, four naval observers, and 17 civilian observers. Most of the observers were from Portsmouth Naval Shipyard. However, two engineers were from Sperry Gyroscope Company, one engineer was from Raytheon Company, and one engineer was from the Naval Ordnance Laboratory.
The observers were there to inspect the submarine’s repairs and help improve her operational performance. Usually, the crew of a Thresher/Permit-class submarine numbers between 104 and 112 personnel. To accommodate the additional personnel, makeshift beds (made from plywood and air mattresses) were constructed in the torpedo room. Visiting officers and civilian engineers packed a suitcase to cover their needs during the cruise.
Only four of Thresher‘s crew were ashore when the boat set sail. One officer had a family emergency, and three enlisted sailors were away from the ship for various other reasons.
Thresher’s first round of tests involved several shallow dives to check the hull’s integrity. A dive to 600 feet was intended to check for leaks. Finding no problems, the skipper communicated to Skylark via the UQC (underwater telephone) that things were fine. Harvey released the rescue ship and arranged to meet Skylark to rendezvous 200 miles east of Cape Cod, past the edge of the continental shelf the following morning. Sea depth beyond that point extended below 8,000 feet.
On the morning of 10 April, the two vessels met up at the pre-determined position and began the next round of tests. At around 0730, Harvey told Skylark, ten miles off the Thresher’s position, that they would start their dive. Harvey communicated to Skylark via the UQC when the Thresher reached depth markers in 15-minute intervals, counting down to her test depth of 1,300 feet.
Thresher reached the halfway point to test depth (650 feet) just after 0800. Just after 0900, Harvey reported that the ship had reached its test depth. Shortly after, Skylark received a message that Thresher was “Experiencing minor difficulty — have a positive angle — attempting to blow — will keep you informed.” After that message, there was one last attempt to communicate, but the message was unintelligible.
What happened aboard Thresher at this point was unknown, but several things had gone wrong. Thresher continued falling further into the cold, dark Atlantic depths. On the surface, Skylark was helpless but continued to attempt to reestablish communications with Thresher. Skylark’s crew tried to tap out messages over the UQC, which might be better understood than voice communication. Eventually, it came to a point where Skylark dropped signal grenades at 15-minute intervals, the simplest way of communicating through hundreds of feet of water.
If the event happened at 09:15 (and we cannot know this with any certainty), then by 09:15:01, it was already too late. An implosion at that depth was instant death for all hands. There was no time for any suffering.
For rescue ships like Skylark, deep-diving submarines presented an entirely new problem – their rescue bells are only safe to around 850 feet. In 1939, the USS Squalus (SS 192) sank during a test dive off the coast of New Hampshire in 240 feet of water. The rescue was successful for 33 men, as shown in this video from the National Archives.
By 1963, however, there had been no substantial improvements in undersea rescue technologies. For example, they could not reach the extraordinary depth of 8,400 feet. After failing to communicate with Thresher, Skylark reported the situation to naval command, including the Commander, Submarine Forces, Atlantic, and the Portsmouth Naval Shipyard. The message reached the highest levels of the government, including the President of the United States, John F. Kennedy, a former surface warfare officer during World War II.
That evening, the crew’s families were notified that the Thresher was “Overdue and Presumed Missing,” a euphemism in use during the World War when submarines did not return on time and disappeared into the depths of the sea.
In search of Thresher
The Navy organized several destroyers and the USS Seawolf (SSN 575) to search for the missing sub. On 11 April 1963, eleven additional ships, including the oceanographic ship Atlantis II and the USS Hazelwood, joined the search. While scanning the ocean floor on 22 April, Atlantis II discovered a “bump” at a depth of 8,400 feet. On 30 April, the USNS Robert D. Conrad (T-AGOR) took the first photographs of the Thresher’s anchor lying on the ocean floor using a camera suspended from a cable.
Once the wreck had been determined within a 100-yard circle, the Navy ordered the bathyscaphe Trieste to the site.[4] Trieste was also equipped with cameras and movable arms to retrieve materials on the ocean floor.
USS Point Defiance (LSD 31) brought the Trieste from California via the Panama Canal, arriving in Boston in late April and returning to California in May. The bathyscaphe fit within the landing craft well of the Point Defiance and was considered the safest way to transfer the submersible from one coast to the other.
Trieste was handed over to the USS Preserver (ASR 8) as her support vessel during the search for the wreck. There were two sets of dives between 24 June and 1 July 1963 and a second set of five dives from 19 August to 1 September 1963. In September 1963, the Department of Defense released a statement that debris from Thresher had been discovered and recovered.
On August 28, Trieste located a large debris field within which was a warped copper pipe, later referred to as the “smoking gun” — believed to have been the cause of Thresher’s demise. After all dives, only bits and pieces of the Thresher had been discovered to verify that she had been lost, but the main portions of the wreck had yet to be found.
The search for Thresher continued in 1964, headed by the Woods Hole Oceanographic Institute and the Naval Research Laboratory (NRL). They used Trieste’s replacement, Trieste II, operating from the USS Mizar (AKA 272). They took a more comprehensive survey of the wreck site, which covered 33 acres. They were able to photograph the ship’s remains in five major sections.
The Court of Inquiry
After contact with the Thresher was lost and it was determined that she would not be recovered, it was time to ask questions about what had happened. Although the exact reasons for Thresher’s loss will never be known, several factors likely contributed to her loss. A court of inquiry was opened on 11 April and did not close until 5 June 1963. Headed by Vice Admiral Bernard L. Austin, the court interviewed 120 witnesses, reviewed 1,700 documents, and examined 255 exhibits.
Among the witnesses were ranking personnel from the Bureau of Ships, Portsmouth Naval Shipyard, and Admiral Hyman Rickover of Naval Nuclear Propulsion and the father of the Nuclear Submarine. By the time the Court concluded on 5 June, the Navy had not even located the wreck and did not have access to much direct evidence. However, even without evidence from the wreck, the Court offered 55 opinions and 19 recommendations.
A primary question was, “What constituted a ‘minor difficulty’ that resulted in a cataclysm taking the lives of 129 people?” The court focused on two main scenarios: a possible leak from one of the water intake pipes that brought seawater in to cool the reactor and a blockage in the compressed air valve to the main ballast tank.
The rationale behind this judgment was that Thresher must have lost power. Without power, the submarine was no longer moving, and this both impeded ascension and prevented the crew from managing incoming and outgoing ballast water through pumps to auxiliary ballast tanks to keep neutral buoyancy.
Another issue was why Thresher could not blow her main ballast tank when they were at test depth. There had been some speculation that compressed air valves connecting the main ballast tank might freeze (shut) at deeper depths during a total release of ballast. To test this possibility, on April 19, the USS Tinosa (SSN 606), sister to Thresher, blew the ballast tanks at a full blow, and the valves froze.
The shipyard put mesh over the reducing valves (which was not required by the specification) to keep particulate matter out. At lower depths, where it is colder, water vapor crystallizes into ice, creating blockage and preventing compressed air from pushing ballast water out from the submarine.
In addition to the technical faults and problems with shipbuilding practices at the time, another problem involved the crew. Only a few onboard officers were qualified submariners or skilled in nuclear propulsion and reactors. Harvey was qualified, having been with the program almost from the start, but the other officers and crew were unprepared for emergencies. The incident during Harvey’s quick cruise in March 1963, where it took the crew 20 minutes to isolate a leak during a drill, emphasized the crew’s incompetence. In the aftermath of Thresher, the training of submarine and nuclear propulsion personnel would change.
Notes:
[1] Although submarines are technically ships of the U.S. Navy, they are traditionally referred to as boats.
[2] HY-80, or High Yield 80, is a low-alloy, high-tensile, high-yield strength steel that’s valued for its strength-to-weight ratio. It’s an iron alloy containing 0.12–0.2% carbon, 2–3.5% nickel, chromium, molybdenum, and copper. These additives give HY-80 increased strength, good plasticity, impact strength, and corrosion resistance. It’s also weldable, allowing for the construction of ships in sections that can be joined together.
[3] ASR = submarine rescue ship.
[4] A bathyscaphe is not a submarine but a complex diving vessel that can ascend to profound depths, including the deepest trench on Earth, the Mariana Trench (36,000 feet).
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