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The second USS Thresher (SSN-593) was the lead ship of her class of nuclear-powered attack submarines in the United States Navy. Her loss at sea during deep-diving tests in 1963 is often considered a watershed event in the implementation of the rigorous submarine safety program SUBSAFE.

The contract to build Thresher was awarded to Portsmouth Naval Shipyardmarker on 15 January 1958, and her keel was laid on 28 May 1958. She was launched on 9 July 1960, was sponsored by Mrs. Frederick B. Warder (wife of the famous Pacific War skipper), and was commissioned on 3 August 1961, with Commander Dean L. Axene in command.

Early career

Thresher conducted lengthy sea trials in the western Atlantic and Caribbean Seamarker areas in 1961 and 1962. These tests provided a thorough evaluation of her many new and complex technological features and weapons. Following these trials, she took part in Nuclear Submarine Exercise (NUSUBEX) 3-61 off the northeastern coast of the United States from 18 September to 24 September 1961.

On 18 October Thresher headed south along the East Coast. While in port at San Juan, Puerto Ricomarker on 2 November 1961, her reactor was shut down and the diesel generator was used to carry the "hotel" electrical loads. Several hours later the generator broke down, and the electrical load was then carried by the battery. The generator could not be quickly repaired, so the captain ordered the reactor restarted. However, the battery charge was depleted before the reactor went critical. With no electrical power for ventilation, temperatures in the machinery spaces reached , and the boat was partially evacuated. Cavalla arrived the next morning and provided power from her diesels, enabling Thresher to restart her reactor.

Thresher conducted further trials and fired test torpedoes before returning to Portsmouth on 29 November. 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, the submarine 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, SC, Thresher undertook operations observed by the Naval Antisubmarine Warfare Council before she returned briefly to New Englandmarker waters, after which she proceeded to Floridamarker for more SUBROC tests. However, while moored at Port Canaveral, Floridamarker, the submarine was accidentally struck by a tug which damaged one of her ballast tanks. After repairs at Groton, Connecticutmarker, by the Electric Boat Company, Thresher went south for more tests and trials off Key West, Floridamarker, then returned northward and remained in dockyard for refurbishment through the early spring of 1963.


On 9 April 1963, after the completion of this work, Thresher, now commanded by Lieutenant Commander John Wesley Harvey, began post-overhaul trials. Accompanied by the submarine rescue ship USS Skylark , she sailed to an area some 350 kilometers (220 statute miles or 190 nautical miles) east of Cape Codmarker, Massachusettsmarker, and on the morning of 10 April started deep-diving tests. As Thresher neared her test depth, Skylark received garbled communications over underwater telephone indicating "... minor difficulties, have positive up-angle, attempting to blow." When Skylark received no further communication, surface observers gradually realized Thresher had sunk. Publicly it took some days to announce that all 129 officers, crewmen, and military and civilian technicians aboard were presumed dead.

After an extensive underwater search using the bathyscaphe Triestemarker, oceanographic ship Mizar and other ships, Thresher’s remains were located on the sea floor, some below the surface, in six major sections. The majority of the debris had spread over an area of about . The major sections were the sail, sonar dome, bow section, engineering spaces section, operations spaces section, and the stern planes.

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 joint in a salt water piping system, 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, 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, which in turn caused a shutdown ("scram") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves. This was later simulated in dock-side tests on Thresher’s sister ship, USS 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 driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly.

Unlike diesel submarines, nuclear subs rely on speed and deck angle rather than deballasting to surface; they are "driven" at an angle towards the surface. Ballast tanks were almost never blown at depth, and to do so could cause the ship to rocket to the surface out of control. Normal procedure was to drive the ship to periscope depth, raise the periscope to verify the area was clear, then blow the tanks and surface the ship.

At the time, reactor-plant operating procedures precluded a rapid reactor restart following a scram, or even the ability to use steam remaining in the secondary system to "drive" the ship 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 ship, 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 her maximum depth and was taking on water. 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 ship to "answer bells" and drive herself to the surface, despite the flooding in the engineering spaces. Admiral Rickover later changed the procedure, allowing steam to be withdrawn from the secondary system in limited quantities for several minutes following a scram.

There was much (covert) criticism of Rickover's training after Thresher went down, the argument being his "nukes" were so well conditioned to protect the nuclear plant they would have shut the main steam stop valves by rote — depriving the ship of needed propulsion — even at great depths and with the ship clearly in jeopardy. Nothing enraged Rickover more than this argument. Common sense, he argued, would prove this to be untrue.

It's more likely that the engine room crew was simply overwhelmed by the flooding casualty, or took too long to contain it. 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, taking on water, and with the reactor shut down, Thresher would not have had anything like 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.

The Thresher probably imploded at a depth somewhere between 1,300 and 2,000 feet (400 and 600m).

Over the next several years, the Navy implemented the SUBSAFE program to correct design and construction problems on all submarines (nuclear and diesel-electric) in service, under construction, and in planning. During the formal inquiry, it was discovered record-keeping at the Portsmouth Naval Shipyard was far from adequate. For example, no one could determine the whereabouts of hull weld X-rays made of Thresher's sister ship Tinosa, nearing completion at Portsmouth, or, indeed, whether they had been made at all. It was also determined that the engine room layout was awkward, in fact dangerous, as there were no centrally-located isolation valves for the main and auxiliary seawater systems. Most subs were subsequently equipped or retrofitted with flood control levers, which allowed the Engineer Officer of the Watch in the maneuvering room to remotely close isolation valves in the seawater systems from a central panel, a task necessarily performed by hand on Thresher. Hand-power valves might not even have been accessible during a flooding casualty: at such depths, the blast of water from even a small leak (a "water spike") can dent metal cabinets, rip insulation from cables, and even cut a man in half. (Water pressure at ] is about ].)

SUBSAFE would prove itself to be a crucial part of the Navy's safe operation of nuclear submarines, but was disregarded just a few years later in a rush to get another nuclear sub, Scorpion, ready for service as part of yet another program meant to increase nuclear submarine availability. The subsequent loss of Scorpion reaffirmed the need for SUBSAFE, and apart from Scorpion, the U.S. Navy has suffered no further losses of nuclear submarines.

The 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 ships. These reports provide specifics on the environmental sampling of sediment, water, and marine life which were taken 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 confirms 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 "Bob" Ballard, the oceanographer credited for the successful search for the wreck of , on a secret mission to map and collect visual data on both the Thresher and the Scorpion wrecks. The Navy used Ballard's search for the Titanic as a screen to hide the mission. Ballard approached the Navy in 1982 for funding to find the 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 the Thresher had sunk so deep it imploded, turning into thousands of pieces. His 1985 search for the Scorpion, which was thought to be a victim of a Soviet attack, revealed such a large debris field that it looked "as though it had been put through a shredding machine." The survey data revealed the most likely cause of the loss of the Scorpion was one of its own torpedoes exploding inside the torpedo room. 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 twelve days to do so, but he used the same debris-field search techniques he had used for the two subs, which worked, and the Titanic was found.

U.S. submarine classes are generally known by the hull number of the lead ship of the class - for instance, Los Angeles-class boats are called 688s because the hull number of USS Los Angeles was SSN-688. The Thresher-class boats should thus be called 593s, but since Thresher's sinking they have been referred to as 594s (Permit class).

The Kingston Trio sang the song "Ballad of the Thresher".

Details of the disaster

Time-accelerated sequence of events during the disaster
The following is from the 1975 book The Thresher Disaster by John Bentley. Times are in 24-hour notation.

  • 07:47: Thresher begins its descent to the test depth of .
  • 07:52: Thresher levels off at , contacts the surface, and the crew inspects the ship for leaks. None are found.
  • 08:09: Commander Harvey reports reaching half the test depth.
  • 08:25: Thresher reaches .
  • 09:02: Thresher is cruising at just a few knots (subs normally moved slowly and cautiously at great depths, lest a sudden jam of the diving planes send the ship below test depth in a matter of seconds.) The boat is descending in slow circles, and announces to Skylark she is turning to "Corpen [course] 090." At this point, transmission quality from the Thresher begins to noticeably degrade, possibly as a result of thermoclines.
  • 09:09: It is believed a brazed pipe-joint ruptures in the engine room. The crew would have attempted to stop the leak; at the same time, the engine room would be filling with a cloud of mist. Under the circumstances, Commander Harvey's likely decision would have been to order full speed, full rise on the sail planes, and blowing main ballast in order to surface. Due to Joule-Thomson effect, the pressurized air rapidly expanding in the pipes cools down, condensing moisture and depositing it on strainers installed in the system to protect the moving parts of the valves; in only a few seconds the moisture freezes, clogging the strainers and blocking the air flow, halting the effort to blow ballast. Water leaking from the broken pipe most likely causes short circuits leading to an automatic shutdown of the ship's reactor, causing a loss of propulsion. The logical action at this point would have been for Harvey to order propulsion shifted to a battery-powered backup system. As soon as the flooding was contained, the engine room crew would have begun to restart the reactor, an operation that would be expected to take at least 7 minutes.
  • 09:12: Skylark pages Thresher on the underwater telephone: "Gertrude check, K [over]." With no immediate response (although Skylark is still unaware of the conditions aboard Thresher), the signal "K" is repeated twice.
  • 09:13: Harvey reports status via underwater telephone. The transmission is garbled, though some words are recognizable: "[We are] experiencing minor difficulty, have positive up-angle, attempting to blow." The submarine, growing heavier from water flooding the engine room, continues its descent, probably tail-first. Another attempt to empty the ballast tanks is performed, again failing due to the formation of ice. Officers on the Skylark could hear the hiss of compressed air over the loudspeaker at this point.
  • 09:14: Skylark acknowledges with a brisk, "Roger, out," awaiting further updates from the SSN. A follow-up message, "No contacts in area," is sent to reassure Thresher she can surface quickly, without fear of collision, if required.
  • 09:15: Skylark queries Thresher about her intentions: "My course 270 degrees. Interrogative range and bearing from you." There is no response, and Skylark's captain, Lieutenant Commander Hecker, sends his own gertrude message to the submarine, "Are you in control?"
  • 09:16: Skylark picks up a garbled transmission from Thresher, transcribed in the ship's log as "900 N." [The meaning of this message is unclear, and was not discussed at the enquiry; it may have indicated the submarine's depth and course, or it may have referred to a Navy "event number" (1000 indicating loss of submarine), with the "N" signifying a negative response to the query from Skylark, "Are you in control?"]
  • 09:17: A second transmission is received, with the partially recognizable phrase "exceeding test depth...." The leak from the broken pipe grows with increased pressure.
  • 09:18: Skylark detects a high-energy low-frequency noise with characteristics of an implosion.
  • 09:20: Skylark continues to page Thresher, repeatedly calling for a radio check, a smoke bomb, or some other indication of the boat's condition.
  • 11:04: Skylark attempts to transmit a message to COMSUBLANT (Commander, Submarines, Atlantic Fleet): "Unable to communicate with Thresher since 0917R. Have been calling by UQC voice and CW, QHB, CW every minute. Explosive signals every 10 minutes with no success. Last transmission received was garbled. Indicated Thresher was approaching test depth.... Conducting expanding search." Radio problems meant that COMSUBLANT did not receive and respond to this message until 12:45. Hecker initiated "Event SUBMISS [loss of a submarine]" procedures at 11:21, and continued to repeatedly hail the Thresher until after 17:00.

On 11 April, at a news conference at 10:30, the Navy officially declared the ship as lost.


Memorial stone in Arlington National Cemetery, USS Thresher, July, 1967
  • Just outside the main gate of the Naval Weapons Station, Seal Beach, Californiamarker, a Thresher-Scorpion Memorial honors the crews of the two submarines.
  • In Carpentersville, ILmarker the Dundee Township Park District named a swimming facility in honor of Thresher.
  • In Portsmouth, New Hampshire, there is a stone memorial with a plaque honoring all who were lost on the Thresher. It is located outside the USS Albacoremarker museum.
  • A Joint Resolution was introduced in 2001 calling for the erection of a memorial in Arlington National Cemeterymarker, but this proposal has yet to be adopted.
  • On 12 April 1963, President John Kennedy issued an Executive Order (No. 11104) paying tribute to the crew of Thresher by flying flags at half-staff.
  • The musician Phil Ochs composed a song detailing the vessel's demise. This song appears on his debut album, All the News That's Fit to Sing. Pete Seeger also composed a song inspired by the vessel.
  • The Thresher's hull number, 593, can be seen on the sailfin of the fictional USS Wayne in the movie The Spy Who Loved Me.
  • 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"

See also


  1. [1]
  2. The Times: Titanic search was cover for secret Cold War subs mission; May 24, 2008
  3. Bentley, John. The Thresher Disaster, New York: Doubleday, 1975, pp. 157-165
  5. [2]
  8. (pdf file)


  • 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 (1998). Blind Man's Bluff: The Untold Story of American Submarine Espionage. Harper. ISBN 0-06-103004-X.
  • Polmar, Norman "Death of the Thresher" The Lyons Press, ISBN 1-58574-348-8
  • Bentley, John "The Thresher Disaster" Doubleday, ISBN 0-385-03057-6
  • Rockwell, Theodore "The Rickover Effect" iUniverse, Inc, ISBN 0-595-74527-X
  • — McCoole's statement re: shutting main steam valves during reactor scram
  • DeMercurio, Michael "The Complete Idiot's Guide to Submarines" Alpha Books, ISBN 978-0028644714

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