USS Thresher (SSN-593)
The second USS Thresher (SSN-593) was the lead ship
Lead ship
The lead ship or class leader is the first of a series or class of ships all constructed according to the same general design. The term is applicable military ships and larger civilian craft.-Overview:...

 of her class of nuclear-powered attack submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s in the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

. 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
SUBSAFE is a quality assurance program of the United States Navy designed to maintain the safety of the nuclear submarine fleet; specifically, to provide maximum reasonable assurance that subs' hulls will stay watertight, and that they can recover from unanticipated flooding.SUBSAFE covers all...


The contract to build Thresher was awarded to Portsmouth Naval Shipyard
Portsmouth Naval Shipyard
The Portsmouth Naval Shipyard , often called the Portsmouth Navy Yard, is a United States Navy shipyard located in Kittery on the southern boundary of Maine near the city of Portsmouth, New Hampshire. It is used for remodeling and repairing the Navy's ships...

 on 15 January 1958, and her keel was laid on 28 May 1958. She was launched
Ship naming and launching
The ceremonies involved in naming and launching naval ships are based in traditions thousands of years old.-Methods of launch:There are three principal methods of conveying a new ship from building site to water, only two of which are called "launching." The oldest, most familiar, and most widely...

 on 9 July 1960, was sponsored by Mrs. Frederick B. Warder (wife of the famous Pacific War skipper), and was commissioned
Ship commissioning
Ship commissioning is the act or ceremony of placing a ship in active service, and may be regarded as a particular application of the general concepts and practices of project commissioning. The term is most commonly applied to the placing of a warship in active duty with its country's military...

 on 3 August 1961, Commander
Commander (United States)
In the United States, commander is a military rank that is also sometimes used as a military title, depending on the branch of service. It is also used as a rank or title in some organizations outside of the military, particularly in police and law enforcement.-Naval rank:In the United States...

 Dean L. Axene commanding.

Early career

Thresher conducted lengthy sea trials in the western Atlantic and Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....

 areas in 1961–1962. These tests provided 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, Thresher headed south along the East Coast. While in port at San Juan, Puerto Rico
San Juan, Puerto Rico
San Juan , officially Municipio de la Ciudad Capital San Juan Bautista , is the capital and most populous municipality in Puerto Rico, an unincorporated territory of the United States. As of the 2010 census, it had a population of 395,326 making it the 46th-largest city under the jurisdiction of...

 on 2 November 1961, her reactor was shut down and the diesel generator
Diesel generator
A diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....

 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
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...

. With no electrical power for ventilation, temperatures in the machinery spaces reached 60 °C (140 °F), and the boat was partially evacuated. arrived the next morning and provided power from her diesels, enabling Thresher to restart her reactor.

Thresher conducted further trials and fired test torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

es 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
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 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 England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

 waters, after which she proceeded to Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 for more SUBROC tests. However, 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
Groton, Connecticut
Groton is a town located on the Thames River in New London County, Connecticut, United States. The population was 39,907 at the 2000 census....

, by the Electric Boat
Electric boat
While a significant majority of water vessels are powered by diesel engines, with sail power and gasoline engines also remaining popular, boats powered by electricity have been used for over 120 years. Electric boats were very popular from the 1880s until the 1920s, when the internal combustion...

 Company, Thresher went south for more tests and trials off Key West, Florida
Key West, Florida
Key West is a city in Monroe County, Florida, United States. The city encompasses the island of Key West, the part of Stock Island north of U.S. 1 , Sigsbee Park , Fleming Key , and Sunset Key...

, 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
Lieutenant Commander
Lieutenant Commander is a commissioned officer rank in many navies. The rank is superior to a lieutenant and subordinate to a commander...

 John Wesley Harvey, began post-overhaul trials. Accompanied by the submarine rescue ship , she sailed to an area some 190 nmi (218.6 mi; 351.9 km) east of Cape Cod
Cape Cod
Cape Cod, often referred to locally as simply the Cape, is a cape in the easternmost portion of the state of Massachusetts, in the Northeastern United States...

, Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

, and on the morning of 10 April started deep-diving tests. As Thresher neared her test depth, Skylark received garbled communications over underwater telephone
Underwater telephone
The underwater telephone also known as UQC , or Gertrude wasdeveloped by the U.S. Navy in 1945 , the UQC underwater telephone is used on all manned submersibles in operation. Voices communicated through the UQC are heterodyned to a high pitch for acoustic transmission through water....

 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
A bathyscaphe is a free-diving self-propelled deep-sea submersible, consisting of a crew cabin similar to a bathysphere, but suspended below a float rather than from a surface cable, as in the classic bathysphere design....

Bathyscaphe Trieste
The Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe with a crew of two, which reached a record maximum depth of about , in the deepest known part of the Earth's oceans, the Challenger Deep, in the Mariana Trench near Guam, on January 23, 1960, crewed by Jacques Piccard ...

, oceanographic ship and other ships, Threshers remains were located on the sea floor, some 8400 ft (2,560.3 m) below the surface, in six major sections. The majority of the debris had spread over an area of about 134000 square metre. The major sections were the sail
Sail (submarine)
In naval parlance, the sail or fin of a submarine is the tower-like structure found on the dorsal surface of submarines...

, 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
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...

 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
A scram or SCRAM is an emergency shutdown of a nuclear reactor – though the term has been extended to cover shutdowns of other complex operations, such as server farms and even large model railroads...

") 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 Threshers sister ship, . 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 submarines 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. Threshers 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
Hyman G. Rickover
Hyman George Rickover was a four-star admiral of the United States Navy who directed the original development of naval nuclear propulsion and controlled its operations for three decades as director of Naval Reactors...

 later changed the procedure, allowing 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, taking on water, and 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 1300–2000 ft (396.2–609.6 m).

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
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

, water, and marine life which were taken to ascertain whether Threshers 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 Ballard
Robert Ballard
Robert Duane Ballard is a former United States Navy officer and a professor of oceanography at the University of Rhode Island who is most noted for his work in underwater archaeology. He is most famous for the discoveries of the wrecks of the RMS Titanic in 1985, the battleship Bismarck in 1989,...

, the oceanographer credited for the successful search for the wreck of , on a secret mission to map and collect visual data on both Thresher and Scorpion
USS Scorpion (SSN-589)
USS Scorpion was a Skipjack-class nuclear submarine of the United States Navy, and the sixth ship of the U.S. Navy to carry that name. Scorpion was declared lost on 5 June 1968 with 99 crew members dying in the incident. The USS Scorpion is one of two nuclear submarines the U.S...

wrecks. 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 it imploded, turning into thousands of pieces. The only recoverable piece was a foot of marled pipe. His 1985 search for 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." 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 subs, which worked, and Titanic was found.

U.S. submarine classes are generally known by the hull number of the lead ship of the class–for instance, -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 Threshers sinking they have been referred to as "594s" (Permit class
Thresher/Permit class submarine
The Thresher/Permit-class was a class of nuclear-powered fast attack submarines in service with the United States Navy from the 1960s until 1994. They replaced the class...


Disaster sequence

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


  • Just outside the main gate of the Naval Weapons Station, Seal Beach, California
    Seal Beach, California
    -Neighborhoods:Seal Beach encompasses the Leisure World retirement gated community with roughly 9,000 residents. This was the first major planned retirement community of its type in the U.S...

    , a Thresher-Scorpion Memorial honors the crews of the two submarines.
  • In Carpentersville, IL 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 Thresher. It is located outside the museum.
  • A Joint Resolution was introduced in 2001 calling for the erection of a memorial in Arlington National Cemetery
    Arlington National Cemetery
    Arlington National Cemetery in Arlington County, Virginia, is a military cemetery in the United States of America, established during the American Civil War on the grounds of Arlington House, formerly the estate of the family of Confederate general Robert E. Lee's wife Mary Anna Lee, a great...

    , 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.
  • 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"
  • 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 the USS Thresher family. -MAS

See also

  • Deep Submergence Rescue Vehicle
    Deep Submergence Rescue Vehicle
    A Deep Submergence Rescue Vehicle is a type of Deep Submergence Vehicle used for rescue of downed submarines and clandestine missions. While DSRV is the term most often used by the United States Navy other nations have different designations for their vehicles.- Chinese models :The People's...

    , the only other American nuclear-powered submarine to be lost at sea, sunk under mysterious circumstances in 1968
  • John Craven USN Key individual in the search for Thresher
  • Hyman G. Rickover
    Hyman G. Rickover
    Hyman George Rickover was a four-star admiral of the United States Navy who directed the original development of naval nuclear propulsion and controlled its operations for three decades as director of Naval Reactors...

External links

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