View source for USS Thresher (SSN-593)

{{otherships|USS Thresher}}
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|Ship image=[[File:USS Thresher;0859306.jpg|300px|USS Thresher (SSN-593) underway, 30 April 1961.]]
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|Ship ordered=15 January 1958
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|Ship builder=[[Portsmouth Naval Shipyard]]
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|Ship laid down=28 May 1958
|Ship launched=9 July 1960
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|Ship commissioned=3 August 1961
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|Ship struck=10 April 1963
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|Ship motto=''Vis Tacita'' (Silent Strength)
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|Ship fate=Sank with all hands during deep diving tests, 10 April 1963, 129 died.
|Ship status=Located 350 km east of Cape Cod at a depth of 8400 ft.
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|Ship class={{Sclass|Permit|submarine}}
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The second '''USS ''Thresher'' (SSN-593)''' was the [[lead boat]] of [[Permit class submarine|her class]] of nuclear-powered attack [[submarine]]s in the [[United States Navy]]. Her loss at sea in the North Atlantic during deep-diving tests approximately 220 miles east of Boston, Massachusetts, on 10 April 1963 was a watershed event for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as [[SUBSAFE]]. Measured by lives lost, historic context and significance, the sinking of ''Thresher'' was then, and remains today, the world's worst submarine disaster. As the first nuclear submarine lost at sea, its disappearance generated international shock and sympathy.

==Significance of design and loss==
When it was designed and built ''Thresher'' was the most advanced attack submarine of its time: it was faster and quieter than any submarine ever built, and able to dive deeper than any submarine in the world. SSN 593 was considered the most advanced weapons system of its day, created specifically to seek out and destroy [[Soviet Union|Soviet]] submarines. Its new sonar (both passive and active) was able to detect other submarines and ships at greater range, and it was intended to launch the U.S. Navy's newest anti-submarine missile, [[SUBROC]]. In writing about its significance shortly after its loss, the (then) Commander of Submarine Force Atlantic – in the March 1964 issue of the U.S. Naval Institute's monthly journal ''Proceedings'' – stated 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 SSNs 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." During its one year of trial operations – August 1961 – July 1962 – the ''Thresher'' fulfilled every expectation as the most advanced nuclear attack submarine in the world.

As the lead vessel, the class name should have been Thresher-class. However, when the ''Thresher'' was struck from the Naval Vessel Register on 16 April 1963, out of respect for naval tradition its name was retired and the class name was changed to that of the second boat, USS ''Permit'' (SSN-594): thus, despite being the lead boat, the ''Thresher'' is, 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==
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 [[ship naming and launching|launched]] on 9 July 1960, was sponsored by Mrs. Mary B. Warder<ref name=Polmar>{{Citation
 | title = The Death of the USS Thresher: The Story Behind History's Deadliest Submarine Disaster
 | author = Polmar, Norman
 | pages = 7
 | isbn = 978-1592283927
}}</ref> (wife of the famous{{peacock-inline|date=August 2013}} Pacific War skipper [[Frederick Warder|Frederick B. Warder]]), and was [[ship commissioning|commissioned]] on 3 August 1961, [[Commander (United States)|Commander]] Dean L. Axene commanding.

''Thresher'' conducted lengthy sea trials in the western [[Atlantic]] and [[Caribbean Sea]] 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 1961, ''Thresher'' headed south along the East Coast. While in port at [[San Juan, Puerto Rico]], 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 mass|critical]]. With no electrical power for ventilation, temperatures in the machinery spaces reached {{convert|60|°C|°F|abbr=on}}, and the boat was partially evacuated. The diesel submarine {{USS|Cavalla|SS-244|2}} arrived the next morning and provided power from her diesels, enabling ''Thresher'' to restart her reactor.<ref>[http://www.cavalla.org/cavthres.html The Cavalla-Thresher Incident]</ref>

''Thresher'' conducted further trials and fired test [[torpedo]]es 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, 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]] 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.<ref>[http://www.navalhistory.org/2013/04/01/uss-thresher-ssn-593-3-august-1961-10-april-1963  "USS Thresher"], article by Vice Admiral E.W. Grenfell, ''U.S. Naval Institute Proceedings'', March 1964; accessed 6 April 2013.</ref>

==Sinking==
On 9 April 1963 ''Thresher'', now commanded by [[Lieutenant Commander]] John Wesley Harvey, got underway from Portsmouth at 8&nbsp;am and rendezvoused with the submarine rescue ship {{USS|Skylark|ASR-20|2}} at 11&nbsp;am to begin its initial post-overhaul dive trials, in an area some {{convert|190|nmi|mi km|abbr=on}} 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. It remained submerged overnight and re-established underwater communications with Skylark at 6:30&nbsp;am on the morning of the 10th to commence deep-dive trials. Following standard practice, Thresher slowly dived deeper as it traveled in circles under Skylark – to remain within communications distance – pausing every additional 100 feet of depth to check the integrity of all systems. As ''Thresher'' neared her test depth, ''Skylark'' received garbled communications over [[underwater telephone]] indicating "...&nbsp;minor difficulties, have positive up-angle, attempting to blow",<ref>{{cite web| url=http://www.csp.navy.mil/othboats/593.htm | title=COMSUBPAC Web site, Submarines Lost or Damaged before and after World War II | accessdate=2006-02-02 |archiveurl = http://web.archive.org/web/20060129171708/http://www.csp.navy.mil/othboats/593.htm |archivedate = 29 January 2006}}</ref><ref>{{cite web| url=http://usgovinfo.about.com/library/weekly/aa081700a.htm | title=U.S. Gov Info / Resources, US Navy's Submarine Rescue Team | accessdate=2006-02-02}}</ref><ref>{{cite web| url=http://www.pbs.org/wgbh/nova/transcripts/2602subsecrets.html | title=NOVA Web site, transcript of "Submarines, Secrets, and Spies" | accessdate=2006-02-02}}</ref> and then a final even more garbled message that included the number "900".<ref>[http://www.navsource.org/archives/08/08593b.htm Thresher (SSN 593) Loss & Inquiry], navsource.org</ref> When ''Skylark'' received no further communication, surface observers gradually realized ''Thresher'' had sunk. By mid-afternoon a total of 15 Navy ships were en route to the search area. At 6:30&nbsp;pm, the Commander Submarine Force Atlantic sent word to Portsmouth Naval Shipyard to begin notifying next-of-kin – starting with Commander Harvey's wife – that Thresher was "missing". By morning the next day all hope of finding Thresher was abandoned and at 10:30&nbsp;am the Chief of Naval Operations 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.<ref>{{cite news | url = http://www.miamiherald.com/2013/04/05/3324654/us-sub-sinking-50-years-ago-led.html | title = US sub sinking 50 years ago led to safety changes | accessdate = 2013-04-05 | last = Sharp | first = David  | agency = [[Associated Press]] | work = [[Miami Herald]]|date=4 April 2013}}{{dead link|date=June 2013}}</ref>

An extensive underwater search using oceanographic ship {{USNS|Mizar|AGOR-11|2}} and other ships mounted immediately and they soon found shattered remains of ''Thresher''{{'}}s hull located on the sea floor, some {{convert|8400|ft|m|abbr=on}} below the surface, in six major sections.<ref name=brand>{{cite journal |author=Brand, V |title=Submersibles&nbsp;– Manned and Unmanned. |journal=South Pacific Underwater Medicine Society Journal |volume=7 |issue=3 |year=1977 |issn=0813-1988 |oclc=16986801 |url=http://archive.rubicon-foundation.org/6154 |accessdate=2008-07-10 }}</ref> The majority of the debris had spread over an area of about {{convert|134000|m2|yd2|abbr=on}}. The [[bathyscaphe]] ''[[bathyscaphe Trieste|Trieste]]'', then in San Diego, California, was alerted on 11 April and subsequently loaded aboard the large landing ship USS ''Point Defiance'' (LSD-31) and brought through the [[Panama Canal]] to Boston. The ''Trieste'' then 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 (submarine)|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 this official US Navy history website: {{cite web|url=http://www.history.navy.mil/photos/sh-usn/usnsh-t/ssn593-k.htm|title=Loss of USS Thresher}}

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,<ref>[http://www.navsea.navy.mil/NewsView.aspx?nw=NewsWires&id=224 50 Years of Steely Purpose-USS Thresher Remembered]. Navsea.navy.mil. 10 April 2013.</ref> 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, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the sub'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, {{USS|Tinosa|SSN-606|2}}. 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.<ref>[http://www.navsource.org/archives/08/08593b.htm Thresher (SSN-593)  Loss & Inquiry]. Navsource.org</ref> Air driers 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 towards the surface. Ballast tanks were almost never blown at depth, and to do so could cause the sub to rocket to the surface out of control. Normal procedure was to drive the sub to periscope depth, raise the periscope to verify the area was clear, then blow the tanks and surface the sub.

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 sub 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 [[Naval Nuclear Power School|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 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 boat to "answer bells" and drive itself to the surface, despite the flooding in the engineering spaces. [[Hyman G. Rickover|Admiral Rickover]] 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 [[implosion (mechanical process)|imploded]] at a depth of {{convert|1300|-|2000|ft|m|abbr=on}}.

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 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 ''[[USS Scorpion (SSN-589)|Scorpion]]'' wrecks.<ref>[http://www.cbsnews.com/stories/2009/11/25/60minutes/main5773673.shtml The Great Explorer] ''[[60 Minutes]]''; aired 29 November 2009</ref> 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.<ref>''Lost Subs: Disaster at Sea''. Tim Kelly, Executive Producer. DVD. [[National Geographic Society|National Geographic]], 2002.</ref> 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 subs, which worked, and ''Titanic'' was found.<ref>[http://web.archive.org/web/20100604054238/http://www.timesonline.co.uk/tol/news/world/us_and_americas/article3994955.ece : Titanic search was cover for secret Cold War subs mission] [[The Times]],24 May 2008</ref>

U.S. submarine classes are generally known by the hull number of the lead ship of the class–for instance, {{USS|Los Angeles|SSN-688|2}}-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" ([[Thresher/Permit class submarine|''Permit'' class]]).

==Disaster sequence==
[[File:Ssn593thresher.gif|thumb|right|375px|Time-accelerated sequence of events during the disaster]]

{{Table
|type=class="wikitable sortable"
|title=Time line of the Thresher disaster<ref>Bentley, John. ''The Thresher Disaster'', New York: Doubleday, 1975, pp. 157–165</ref>
|hdrs=Time!!Event
|row1=07:47{{!!}}''Thresher'' begins its descent to the test depth of {{convert|1000|ft|m|abbr=on}}.
|row2=07:52{{!!}}''Thresher'' levels off at {{convert|400|ft|m|abbr=on}}, contacts the surface, and the crew inspects the ship for leaks. None are found.
|row3=08:09{{!!}}Commander Harvey reports reaching half the test depth.
|row4=08:25{{!!}}''Thresher'' reaches {{convert|1000|ft|m|abbr=on}}.
|row5=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 ''Thresher'' begins to noticeably degrade, possibly as a result of [[thermocline]]s.
|row6=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 fairwater planes, and blowing main ballast in order to surface. The pressurized air rapidly expanding in the pipes [[Joule-Thomson effect|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 [[scram|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&nbsp;minutes.
|row7=09:12{{!!}}''Skylark'' pages ''Thresher'' on the underwater telephone: "[[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.
|row8=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 ''Skylark'' could hear the hiss of compressed air over the loudspeaker at this point.
|row9=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.
|row10=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 [[Underwater telephone|gertrude message]] to the submarine, "Are you in control?"
|row11=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?"]
|row12=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.
|row13=09:18{{!!}}''Skylark'' detects a high-energy low-frequency noise with characteristics of an implosion.
|row14=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.
|row15=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 [[underwater telephone|UQC]] voice and [[Morse code|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 ''Thresher'' until after 17:00.
}}
On 11 April, at a Pentagon news conference at 10:30, the [[Chief of Naval Operations]], Admiral [[George W. Anderson Jr.]], officially declared the ship as lost.

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.”<ref>{{cite web|url=http://engineering.vanderbilt.edu/news/2013/vanderbilt-ties-to-%E2%80%98worst-submarine-tragedy%E2%80%99-50-years-ago/ |title=Vanderbilt ties to 'worst submarine tragedy' 50 years ago &#124; News &#124; School of Engineering &#124; Vanderbilt University |publisher=Engineering.vanderbilt.edu |date= |accessdate=2013-04-23}}</ref>

==Alternate theory of the sinking (electrical failure) ==
Bruce Rule, an acoustic data expert, published his analysis of the data collected by USS ''Skylark'' and Atlantic [[SOSUS]] arrays in a paper<ref>[http://www.designed4submariners.com/uploads/Docs_Thresher_and_Scorpion_Loss.pdf "What Sank The Thresher"], Bruce Rule, 10 April 2013</ref> which was published in the ''Navy Times''<ref>[http://www.navytimes.com/article/20130404/NEWS/304040021/50-years-later-look-what-really-sank-Thresher "50 years later, a look at what really sank the ''Thresher''"], Bruce Rule and Norman Polmar, 4 April 2013 (''Navy Times'' link)</ref> on 8 April 2013.<ref name="navtimespdf">[http://www.designed4submariners.com/uploads/Thresher_Report.pdf "What Sank The Thresher"], Bruce Rule and Norman Polmar, 8 April 2013</ref> Rule's analysis is based on SOSUS data which 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.<ref name="navtimespdf"/>

Rule concluded that the primary cause of the sinking was a failure of the electrical bus which was powering the main coolant pumps.  According to Rule, SOSUS data indicates that after two minutes of electrical instability, the bus failed at 0911, causing the main coolant pumps to trip off.  This caused an immediate reactor scram, resulting in a loss of propulsion.  Inability to de-ballast the ship caused by formation of ice in the high-pressure air pipes then caused the ''Thresher'' to sink.  Rule's analysis holds that flooding (whether from a silver brazed joint or anywhere else) did not play any role in the reactor scram or the sinking, and that the ''Thresher'' was intact until it imploded.  In addition to the SOSUS data that does not record any sound of flooding, the crew of the ''Skylark'' did not report hearing any noise that sounded like flooding, and the ''Skylark'' was able to communicate with the ''Thresher'', despite the fact that even a small leak at test depth would have produced a deafening roar.  Additionally, the previous commander of the ''Thresher'' testified that he would not have described flooding, even from a small diameter pipe, as a "minor problem".<ref name="navtimespdf"/>

Rule interprets the communication "900" from the ''Thresher'' at 0917 as a reference to test depth, signifying that the ''Thresher'' was nine hundred feet below its test depth of 1,300, or 2,200 feet 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, four hundred feet below its certified test depth.  The implosion took 0.1 seconds, too fast for the human nervous system to perceive.<ref name="navtimespdf"/>

==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 the [[USS Scorpion (SSN-589)]], which sank in 1968 for reasons still undetermined: the ''Scorpion'' was not SUBSAFE certified.<ref>{{cite web|url=http://www.seacoastonline.com/articles/20130324-NEWS-303240357| title = USS Thresher Left Legacy of Safety for Submarines|publisher=SeaCoast online, 24 March 2013.}}</ref>

==Memorials==
[[File:6707-ArlingtonCemetary-USS ThresherMemorialStone.png|thumb|upright|Memorial stone in Arlington National Cemetery, USS ''Thresher'', July 1967]]

*Just outside the main gate of the Naval Weapons Station, [[Seal Beach, California]], a ''Thresher''-''Scorpion'' Memorial honors the crews of the two submarines.<ref>{{cite web|url=http://www.submarinehistory.com/ThresherScorpionMemorial.html |title=ThresherScorpionMemorial |publisher=Submarinehistory.com |accessdate=2010-06-01}}</ref>
*In [[Carpentersville, IL]] the Dundee Township Park District named a swimming facility in honor of ''Thresher''.{{Citation needed|date=June 2008}}
*In Portsmouth, New Hampshire, there is a stone memorial with a plaque honoring all who were lost on ''Thresher''. It is located outside the {{USS|Albacore|AGSS-569|2}} museum.<ref>{{cite web|url=http://www.waymarking.com/waymarks/WM52XP |title=Wreck of USS Thresher (SSN-593)&nbsp;– Portsmouth, NH&nbsp;– Disaster Memorials on |publisher=Waymarking.com |accessdate=2010-06-01}}</ref>
*The Portsmouth Navy Yard, where the ''Thresher'' was built, renamed its on-base chapel the Thresher Memorial Chapel after the disaster.<ref>{{cite book|first=Richard E. |last=Winslow III|title=Portsmouth-Built: Submarines of the Portsmouth Naval Shipyard|page=161|publisher=Portsmouth Marine Society|year=1985|isbn=091581904X}}</ref>
*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.<ref>{{cite web|first=Michael |last=Robert Patterson |url=http://www.arlingtoncemetery.net/uss-thresher.htm |title=USS Thresher Disaster |publisher=Arlingtoncemetery.net |accessdate=2010-06-01}}</ref>
*On 12 April 1963, President [[John Kennedy]] issued {{Executive Order|11104}} paying tribute to the crew of ''Thresher'' by flying flags at half-staff.<ref>[http://web.archive.org/web/20051115062550/http://www.lib.umich.edu/govdocs/jfkeo/eo/11104.htm Executive Order 11104<!-- Bot generated title -->]</ref>
*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"<ref>[http://www.eureka.mo.us/MINUTES/2007PARK_BOARD/Park_Board_Minutes_4-10-07.pdf www.eureka.mo.us/MINUTES/2007PARK_BOARD/Park_Board_Minutes_4-10-07.pdf] (pdf file) {{dead link|date=April 2013}}</ref>
*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.
*In Nutley, New Jersey, a monument to Pervis Robison, Jr. http://www.flickr.com/photos/sheenachi/145949526/
*On 7 April 2013 the 50th anniversary of the loss of the Thresher, the Town of Kittery, Maine held ceremonies at the Kittery Memorial Circle to dedicate a 129 foot flagpole erected to honor the 129 lost souls that died on the Thresher. Kittery also plans a Thresher monument in Memorial Park at the entrance to the new Memorial Bridge.
*''Thresher''′s hull number was used for an attack submarine in the [[James Bond]] movie ''[[The Spy Who Loved Me (film)|The Spy Who Loved Me]]''.

==See also==
*[[Deep Submergence Rescue Vehicle]]
*{{USS|Scorpion|SSN-589}}, the only other American nuclear-powered submarine to be lost at sea (under mysterious circumstances), in 1968
*[[John Craven USN]] Key individual in the search for ''Thresher''
*[[Russian submarine K-141 Kursk]]

==Footnotes==
{{reflist|30em}}

==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: {{cite web|url=http://www.navalhistory.org/2013/04/01/uss-thresher-ssn-593-3-august-1961-10-april-1963|title=USS Thresher (SSN-593) 3 August 1961 – 10 April 1963}}
* [http://www.submarinehistory.com/Thresher.html Loss of USS Thresher]
* [http://www.submarinehistory.com/ThresherScorpionMemorial.html Thresher-Scorpion Memorial]
*[http://www.submarinehistory.com/WWIISubmarineMemorial.html World War II National Submarine Memorial&nbsp;– West]
*[http://www.submarinehistory.com/WWIISubmarineMemorial-East.html World War II National Submarine Memorial&nbsp;– East]
*{{cite book | last = Sontag | first = Sherry |first2= Christopher|last2= Drew|first3=Annette Lawrence |last3=Drew | title = [[Blind Man's Bluff: The Untold Story of American Submarine Espionage]] | publisher = HarperPaperbacks | location = New York | year = 1999 | isbn = 0-06-103004-X }}
* {{cite book | last = Polmar | first = Norman | title = Death of the Thresher | publisher = Chilton Books | location = Philadelphia | year = 1964 | 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 "The Thresher Disaster" Doubleday, ISBN 0-385-03057-6
* {{cite book | last = Bentley | first = John | title = The Thresher disaster; the most tragic dive in submarine history | publisher = Doubleday | location = Garden City, N.Y | year = 1975 | isbn = 0-385-03057-6 }}
*{{cite book | last = Rockwell | first = Theodore | title = The Rickover Effect : How One Man made a Difference | publisher = IUniverse | location = Lincoln | year = 2002 | isbn = 0-595-74527-X }}
*[http://archiver.rootsweb.com/th/read/USS-THRESHER-SSN593/2005-01/1104944120 McCoole's statement re: shutting main steam valves during reactor scram]
* {{cite book|last=DiMercurio|first=Michael|title=The complete idiot's guide to submarines|year=2003|publisher=Alpha Books|location=Indianapolis|isbn=978-0-02-864471-4|last2=Benson|first2=Michael}}

==Further reading==
*{{cite book|author=Joint Committee on Atomic Energy (United States Congress)|title=Loss of the U.S. S. "Thresher.": Hearings, Eighty-eighth Congress, first and second sessions|url=http://books.google.com/books?id=uKAJmmtgIUEC|accessdate=5 April 2013|year=1965|publisher=Govt. Print. Off.}}
* 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.

==External links==
{{Commons category|USS Thresher (SSN-593)}}
*[http://www.oneternalpatrol.com/uss-thresher-593.htm On Eternal Patrol: USS ''Thresher'']
*http://www.ussthresher.com/
*http://www.thresherbase.org/
*[http://www.youtube.com/watch?v=r0bRA1hp23w Memorial Video on YouTube]

{{Permit class submarine}}

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[[Category:United States submarine accidents]]
[[Category:Permit-class submarines]]
[[Category:Cold War submarines of the United States]]
[[Category:Lost submarines of the United States]]
[[Category:Sunken nuclear submarines]]
[[Category:Nuclear-powered ships]]
[[Category:Nuclear ships of the United States Navy|Thresher, USS]]
[[Category:Maritime incidents in 1963]]
[[Category:Shipwrecks in the Atlantic Ocean|Thresher, USS]]
[[Category:Ships built in Maine]]
[[Category:1960 ships]]
[[Category:1963 in the United States]]
[[Category:Ships lost with all hands]]

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