USS Thresher (SSN-593)

USS Thresher (SSN-593) underway, 30 April 1961.
History
United States
Name:	Thresher
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.
Status:	Located 350 km east of Cape Cod at a depth of 8,400 ft (2,560 meters).
General characteristics
Class and type:	Thresher-class submarine
Displacement:	3,540 short tons (3,210 t) light, 3,770 short tons (3,420 t) submerged
Length:	279 ft (85 m)
Beam:	32 ft (9.8 m)
Draft:	26 ft (7.9 m)
Propulsion:	1 Westinghouse S5W PWR, Westinghouse Geared Turbines 15,000 shp (11 MW)
Speed:	33 knots (61 km/h; 38 mph)
Complement:	16 officers, 96 men
Armament:	4 × 21 in (530 mm) torpedo tubes amidships

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 220 miles (350 km) east of Boston, Massachusetts, killing all 129 crew and shipyard personnel aboard in the deadliest submarine disaster ever.^[1][2] 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 first of only two submarines that killed more than 100 people aboard; the other was the Russian Kursk, which sank with 118 aboard in 2000.

Significance of design and loss

At the time she was built, Thresher was the fastest (matching the smaller, contemporary Skipjack class) and quietest submarine in the world. She was also considered the most advanced weapons system of her day. Created specifically to find and destroy Soviet submarines, the ship boasted a new sonar system whose passive and active modes could detect other vessels at greater range, and she was intended to launch the U.S. Navy's newest anti-submarine missile, the SUBROC. Shortly after her loss, the Commander of Submarine Force Atlantic wrote in the March 1964 issue of the U.S. Naval Institute's monthly journal Proceedings that "the Navy had depended upon this performance to the extent that it had asked for and received authority to build 14 of these ships, as well as an additional 11 submarines with very much the same characteristics. This was the first time since World War II that we had considered our design sufficiently advanced to embark upon construction of a large class of general-purpose attack submarines."

Following Navy tradition, this class of subs was originally named Thresher after the lead boat. When Thresher was struck from the Naval Vessel Register on 16 April 1963, the class name was changed to that of the second boat, Permit, and Thresher is now officially referred to as a Permit-class submarine. Having been "lost at sea," Thresher was not decommissioned by the U.S. Navy and remains on "Eternal Patrol."

Early career

Thresher at sea on 24 July 1961

The contract to build Thresher was awarded to Portsmouth Naval Shipyard on 15 January 1958, and her keel was laid on 28 May 1958. She was launched on 9 July 1960, was sponsored by Mrs. Mary B. Warder^[2] (wife of World War II skipper Frederick B. Warder), and was commissioned on 3 August 1961, Commander Dean L. Axene commanding.

Thresher conducted lengthy sea trials in the western Atlantic and Caribbean Sea areas in 1961–1962. These tests allowed a thorough evaluation of her many new and complex technological features and weapons. She took part in Nuclear Submarine Exercise (NUSUBEX) 3–61 off the northeastern coast of the United States from 18–24 September 1961.

On 18 October 1961, Thresher, in company with the diesel-electric submarine Cavalla, headed south on a 3-week test and training cruise to San Juan, Puerto Rico, arriving 2 November. Following customary procedure while in port, her reactor was shut down. Since no shore power connection was available in San Juan, the ship's backup diesel generator was used to carry the "hotel" electrical loads. Several hours later, the backup generator broke down and the electrical load was transferred to the ship's battery. As most of the battery power was needed to keep vital systems operating and to restart the reactor, lighting and air-conditioning were shut down. Without air-conditioning, temperature and humidity in the submarine rose, reaching 60 °C (140 °F) after about ten hours. The crew attempted to repair the diesel generator (four men would receive Navy Commendation Medals for their work that night). After it became apparent that the generator could not be fixed before the battery was depleted, the crew tried to restart the reactor, but the remaining battery charge was insufficient. The captain, returning to the ship from a shore function, arrived just after the battery ran down. The crew eventually borrowed cables from another ship in the harbor and connected them to the adjacent Cavalla, which started her diesels and provided enough power to allow Thresher to restart her reactor.^[3]

Thresher conducted further trials and fired test torpedoes before returning to Portsmouth on 29 November 1961. The boat remained in port through the end of the year, and spent the first two months of 1962 evaluating her sonar and Submarine Rocket (SUBROC) systems. In March, she participated in NUSUBEX 2–62 (an exercise designed to improve the tactical capabilities of nuclear submarines) and in antisubmarine warfare training with Task Group ALPHA.

Off Charleston, South Carolina, Thresher undertook operations supporting development of the SUBROC anti-submarine missile. She returned briefly to New England waters, after which she proceeded to Florida for more SUBROC tests. While moored at Port Canaveral, Florida, the submarine was accidentally struck by a tug which damaged one of her ballast tanks. After repairs at Groton, Connecticut, by the Electric Boat Company, Thresher went south for more tests and trials off Key West, Florida, then returned northward. The submarine entered Portsmouth Shipyard on 16 July 1962 to begin a scheduled 6-month post-shakedown availability to examine systems and make repairs and corrections as necessary. As is typical with a first-of-class boat, the work took longer than expected, lasting nearly 9 months. The ship was finally re-certified and undocked on 8 April 1963.^[4]

Sinking

On 9 April 1963, Thresher, commanded by Lieutenant Commander John Wesley Harvey, got underway from Portsmouth at 08:00 and rendezvoused with the submarine rescue ship Skylark at 11:00 to begin her initial post-overhaul dive trials, in an area some 190 nautical miles (220 miles; 350 kilometres) east of Cape Cod, Massachusetts. That afternoon Thresher conducted an initial trim dive test, surfaced and then performed a second dive to half test depth. She remained submerged overnight and re-established underwater communications with Skylark at 06:30 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 additional 100 feet (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",^[5][6][7] and then a final even more garbled message that included the number "900".^[8] When Skylark received no further communication, surface observers gradually realized Thresher had sunk.

By mid-afternoon, 15 Navy ships were en route to the search area. At 18:30, the Commander, Submarine Force Atlantic, sent word to Portsmouth Naval Shipyard to begin notifying next-of-kin – starting with Commander Harvey's wife, Irene Harvey^[9] – that Thresher was missing.

By morning on 11 April, all hope of finding Thresher was abandoned, and at 10:30 the Chief of Naval Operations (CNO) 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 on 12–15 April in honor of the 129 lost submariners and shipyard personnel.^[10]

Search and recovery

US Navy ships circle in the vicinity of the site of Thresher's sinking on 15 April 1963

The Navy quickly mounted an extensive underwater search using the oceanographic ship Mizar and other ships; they soon found shattered remains of Thresher's hull on the sea floor, some 8,400 ft (2,600 m) below the surface, in six major sections.^[11] Most of the debris had spread over an area of about 134,000 m² (160,000 sq yd). The bathyscaphe Trieste, then in San Diego, California, was alerted on 11 April and loaded aboard the large landing ship Point Defiance and brought through the Panama Canal to Boston. Trieste was deployed for two series of dives on the debris field: the first series on 24–30 June, and the second series in late August/early September. It found and photographed major sections of Thresher, including the sail, sonar dome, bow section, engineering spaces section, operations spaces section, and the stern planes. One aspect of the search conducted that summer by Mizar involved the use of highly sensitive proton magnetometers furnished by the Instrument Division of Varian Associates, Palo Alto, California, and shipped aboard Mizar before her departure from Suitland, Maryland. The magnetometers were used in conjunction with underwater video cameras and suspended on the same electrical line used to tow the video cameras themselves. Sea-bottom photography of the wreck site taken in summer 1963 can be seen at the official US Navy history website.^[12]

Trieste's successor Trieste II incorporated parts of the original bathyscaphe and was completed in early 1964. The bathyscaphe was placed on board USNS Private Francis X. McGraw and also shipped, via the Panama Canal, to Boston. Additional operations were conducted at the loss site of Thresher that were commenced by the first Trieste the year before. Trieste II was Commanded by Lt Comdr. John B. Mooney, Jr., with co-pilot Lt. John H. Howland and Capt. Frank Andrews in an operation that recovered bits of wreckage of the lost Thresher, in September 1964. The groundbreaking deep submergence operations helped in the design and construction of other deep-diving submersibles which could be used in rescuing crews and recovering objects from submarines in distress below levels reachable by conventional methods.

Overhead view of Thresher's upper rudder, photographed in October 1964 from a deep-sea vehicle deployed from USNS Mizar

Deep-sea photography, recovered artifacts, and an evaluation of her design and operational history permitted a Court of Inquiry to conclude Thresher had probably suffered the failure of a salt-water piping system joint which relied heavily on silver brazing instead of welding. Earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints,^[13] most of which were determined not to pose a risk significant enough to require a repair. 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 which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side 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.^[14] Air dryers were later retrofitted to the high-pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly.

Subsequent study of SOSUS (sound surveillance system) data from the time of the incident has given rise to doubts of whether flooding preceded the reactor scram, as no sound of the high pressure water impacting the compartments of the submarine could be detected on instrument recordings from SOSUS at the time. Such flooding would have been a significant sonic event, and no evidence of that can be found in the recorded data.^[15]

Submarines typically rely on speed and deck angle (angle of attack) rather than deballasting to surface; they are propelled at an angle towards the surface. Ballast tanks were almost never blown at depth, and 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 the area was clear, then blow the tanks and surface the submarine.

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 over-rapid cool-down of the reactor. Thresher's Reactor Control Officer, Lieutenant Raymond McCoole, was not at his station in the maneuvering room, or indeed on the boat, during the fatal dive. McCoole was at home caring for his wife who had been injured in a household accident – he had been all but ordered ashore by a sympathetic Commander Harvey. McCoole's 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 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 later changed the procedure, creating the "Fast Recovery Startup" procedure. The Fast Recovery Startup allows an immediate reactor restart and for steam to be withdrawn from the secondary system in limited quantities for several minutes following a scram.

In a dockside simulation of flooding in the engine room, held before Thresher sailed, it took the watch in charge 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.

Thresher likely imploded at a depth of 1,300–2,000 ft (400–610 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 specifics on the environmental sampling of sediment, water, and marine life which was done 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.

According to newly declassified information, the Navy sent Commander (Dr.) Robert Ballard, the oceanographer credited with locating the wreck of RMS Titanic, on a secret mission to map and collect visual data on both Thresher and Scorpion wrecks.^[16] The Navy used Ballard's search for Titanic as a screen to hide the mission. Ballard approached the Navy in 1982 for funding to find Titanic with his new deep-diving robot submersible. The Navy saw the opportunity and granted him the money on the condition he first inspect the two submarine wrecks. Ballard's robotic survey discovered that Thresher had sunk so deep that it imploded, turning into thousands of pieces. The only recoverable piece was a foot of marled pipe.^[17] His 1985 search for Scorpion revealed such a large debris field that it looked "as though it had been put through a shredding machine." Once the two wrecks had been visited, and the radioactive threat from both was established as small, Ballard was able to search for Titanic. Due to dwindling funds, he had just 12 days to do so, but he used the same debris-field search techniques he had used for the two submarines, which worked, and Titanic was found.^[18]

Disaster sequence of 10 April 1963

Time-accelerated sequence of events during the disaster

During the 1963 inquiry, Admiral Hyman Rickover stated:

I believe the loss of the Thresher should not be viewed solely as the result of failure of a specific braze, weld, system or component, but rather should be considered a consequence of the philosophy of design, construction and inspection that has been permitted in our naval shipbuilding programs. I think it is important that we re-evaluate our present practices where, in the desire to make advancements, we may have forsaken the fundamentals of good engineering.^[20]

Alternative theory of the sinking: electrical failure

On April 8, 2013, Bruce Rule, an acoustic data expert, published his own analysis of the data collected by USS Skylark and Atlantic SOSUS arrays in a paper^[21] in the Navy Times.^[22][23] Rule based his analysis on SOSUS data that was highly classified in 1963 and was not discussed in open session of the Court of Inquiry and was not revealed at the congressional hearings.^[23]

Rule concluded that the primary cause of the sinking was a failure of the electrical bus that powered the main coolant pumps. According to Rule, SOSUS data indicates that after two minutes of electrical instability, the bus failed at 9:11 a.m., causing the main coolant pumps to trip off. This caused an immediate reactor scram, resulting in a loss of propulsion. Thresher could not be deballasted because ice had formed in the high-pressure air pipes, and so she sank. Rule's analysis holds that flooding (whether from a silver brazed joint or anywhere else) played no role in the reactor scram or the sinking, and that Thresher was intact until she imploded. In addition to the SOSUS data that does not record any sound of flooding, the crew of Skylark did not report hearing any noise that sounded like flooding, and Skylark was able to communicate with Thresher, despite the fact that, at test depth, even a small leak would have produced a deafening roar. Additionally, the previous commander of Thresher testified that he would not have described flooding, even from a small-diameter pipe, as a "minor problem".^[23]

Rule interprets the communication "900" from Thresher at 9:17 a.m. as a reference to test depth, signifying that Thresher was 900 feet (270 m) below her test depth of 1,300 feet (400 m), or 2,200 feet (670 m) below sea level. According to Rule the SOSUS data indicates an implosion of Thresher at 09:18:24, at a depth of 2,400 feet (730 m), 400 feet (120 m) below her predicted collapse depth. The implosion took 0.1 seconds, too fast for the human nervous system to perceive.^[23]

SUBSAFE legacy

When the Court of Inquiry delivered its final report, it recommended that the Navy implement a more rigorous program of design review and safety inspections during construction. That program, launched in December 1963, was known as SUBSAFE. From 1915 to 1963, the U.S. Navy lost a total of 16 submarines to non-combat accidents. Since the inception of SUBSAFE only one submarine has suffered a similar fate, and that was USS Scorpion, which sank in 1968 for reasons still undetermined. Scorpion was not SUBSAFE certified.^[24]

Memorials

Memorial stone for a lost USS Thresher sailor, Arlington National Cemetery, July 1967

• 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.^[25]
• The Portsmouth Navy Yard, where Thresher was built, renamed its on-base chapel the Thresher Memorial Chapel after the disaster.^[26]
• In Portsmouth, New Hampshire, there is a stone memorial with a plaque honoring all who were lost on Thresher. It is outside the Albacore museum.^[27]
• Just outside the main gate of the Naval Weapons Station, Seal Beach, California, a Thresher-Scorpion Memorial honors the crews of the two submarines.^[28]
• In Eureka, Missouri, there is a marble stone at the post office on Thresher Drive honoring the "officers and crew of the USS Thresher, lost 10 April 1963."^[29]
• In Salisbury, Massachusetts, the town paid tribute to USS Thresher crewman Sonarman First Class Robert Edwin Steinel, a resident of the town, by naming a park in his honor "Robert E. Steinel Memorial Park". The tribute ceremony was attended by his wife, children, and other members of USS Thresher family.
• In Nutley, New Jersey, there is a monument to Thresher crewmember Pervis Robison, Jr.^[30]
• In Denville, New Jersey, there is a monument to Thresher crewmember Robert D. Kearney at the Gardner Field recreation area.^[31]
• In Carpentersville, Illinois, the Dundee Township Park District named a swimming facility (now closed and demolished) in honor of Thresher.
• Thresher Avenue, named for the submarine, serves a residential area in Naval Base Kitsap in Washington state.^[32]
• A joint resolution was introduced in 2001 calling for the erection of a memorial in Arlington National Cemetery, but this proposal has yet to be adopted.^[33]
• On 7 April 2013, the 50th anniversary of the loss of Thresher, the town of Kittery, Maine, held ceremonies at the Kittery Memorial Circle to dedicate a 129-foot (39 m) flagpole erected to honor the 129 lost souls who died on Thresher. There is also a Thresher monument in Memorial Park next to the Kittery Town Hall.^[34]
• Naval Submarine Base, Groton Connecticut named an enlisted barracks "Thresher Hall" after the submarine and mounted a plaque in its lobby displaying the names of the crew members and contractors that were lost.

See also

• Deep Submergence Rescue Vehicle
• USS Scorpion (SSN-589), the only other American nuclear-powered submarine to be lost at sea
• John P. Craven, a key individual in the search for Thresher
• Kursk submarine disaster, next largest loss of life on a submarine
• List of sunken nuclear submarines
• List of lost United States submarines

Footnotes

References

• One of the earliest and most comprehensive accounts of the loss of the Thresher was written by Vice Admiral E.W. Grenfell, Commander Submarine Force Atlantic, and published in March 1964 in the U.S. Navy's professional journal Proceedings; on 1 April 2013, on the occasion of the 50th anniversary, the U.S. Naval Institute has re-posted Admiral Grenfell's detailed account: "USS Thresher (SSN-593) 3 August 1961 – 10 April 1963".
• Loss of USS Thresher
• Thresher-Scorpion Memorial
• World War II National Submarine Memorial – West
• World War II National Submarine Memorial – East
• Sontag, Sherry; Drew, Christopher; Drew, Annette Lawrence (1999). Blind Man's Bluff: The Untold Story of American Submarine Espionage. New York: HarperPaperbacks. ISBN 0-06-103004-X.
• Polmar, Norman (1964). Death of the Thresher. Philadelphia: Chilton Books. ISBN 1-58574-348-8. First published 1964; reissued in 2001 by Lyons Press (Guilford, Conn) as The Death of the USS Thresher
• Bentley, John (1975). The Thresher Disaster: The Most Tragic Dive in Submarine History. Garden City, N.Y: Doubleday. ISBN 0-385-03057-6.
• Rockwell, Theodore (2002). The Rickover Effect: How One Man made a Difference. Lincoln: IUniverse. ISBN 0-595-74527-X.
• McCoole's statement re: shutting main steam valves during reactor scram
• DiMercurio, Michael; Benson, Michael (2003). The Complete Idiot's Guide to Submarines. Indianapolis: Alpha Books. ISBN 978-0-02-864471-4.

Further reading

• Joint Committee on Atomic Energy (United States Congress) (1965). Loss of the U.S.S. "Thresher": Hearings, Eighty-eighth Congress, first and second sessions. Govt. Print. Off. Retrieved 5 April 2013.
• U.S. Atlantic Fleet. Staff, Deputy Commander Submarine Force. (1964) United States Ship Thresher (SSN 593): In memoriam 10 April 1963. U.S. Navy Atlantic Fleet. No Available ISBN.
• Thresher's ship number 593 is interesting as a "good" prime number, as discussed at 593.

External links

Wikimedia Commons has media related to USS Thresher (SSN-593).

• On Eternal Patrol: USS Thresher
• Photo gallery of Thresher at NavSource.org
• http://www.ussthresher.com/
• http://www.thresherbase.org/
• Memorial Video on YouTube

Coordinates: 41°46′N 65°03′W / 41.767°N 65.050°W / 41.767; -65.050