USS Scorpion (SSN-589)
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USS Scorpion (SSN-589) 22 August 1960 off New London, Connecticut.
|Ordered:||31 January 1957|
|Builder:||General Dynamics Electric Boat|
|Laid down:||20 August 1958|
|Launched:||29 December 1959|
|Commissioned:||29 July 1960|
|Struck:||30 June 1968|
|Fate:||Sank on 22 May 1968; cause of sinking unknown. All 99 on board killed.|
|Status:||Located on the seabed of the Atlantic Ocean,  in 3,000 m (9,800 ft) of water, 740 km (400 nmi) southwest of the Azores,|
|Class & type:||Skipjack-class submarine|
|Displacement:||2,880 long tons (2,930 t) light
3,075 long tons (3,124 t) full
195 long tons (198 t) deadweight
|Length:||76.8 m (252 ft 0 in)|
|Beam:||9.7 m (31 ft 10 in)|
|Draft:||9.1 m (29 ft 10 in)|
|Complement:||8 officers, 75 men|
|Armament:||6 × 21 in (533 mm) torpedo tubes
2 × Mark 45 torpedoes
USS Scorpion (SSN-589) was a Skipjack-class nuclear submarine of the United States Navy, and the sixth vessel of the U.S. Navy to carry that name. Scorpion was declared lost on 5 June 1968 with 99 crewmen dying in the incident. The USS Scorpion is one of two nuclear submarines the U.S. Navy has lost, the other being USS Thresher (SSN-593). In November 2012, the U.S. Submarine Veterans, an organization with over 13,800 members (all former submariners) asked the US Navy to reopen the investigation on the sinking of USS Scorpion.
Service history 
Scorpion's keel was laid down on 20 August 1958 by the Electric Boat Division of the General Dynamics Corporation in Groton, Connecticut. She was launched on 19 December 1959, sponsored by Mrs. Elizabeth S. Morrison (daughter of the last commander of the World War II-era USS Scorpion, which had been lost with all hands in 1944), and commissioned on 29 July 1960, Commander Norman B. Bessac in command.
Assigned to Submarine Squadron 6, Division 62, Scorpion departed New London, Connecticut, on 24 August for a two-month deployment in European waters. During that period, she participated in exercises with units of the 6th Fleet and of other NATO navies. After returning to New England in late October, she trained along the eastern seaboard until May 1961, then crossed the Atlantic again for operations which took her into the summer. On 9 August 1961 she returned to New London, a month later, shifted to Norfolk, Virginia. In 1962, she earned the Navy Unit Commendation.
With Norfolk her home port for the remainder of her career, Scorpion specialized in the development of nuclear submarine warfare tactics. Varying her role from hunter to hunted, she participated in exercises which ranged along the Atlantic coast and in the Bermuda and Puerto Rico operating areas; then, from June 1963 – May 1964, she interrupted her operations for an overhaul at Charleston, South Carolina. Resuming duty off the eastern seaboard in late spring, she again interrupted that duty from 4 August – 8 October to make a transatlantic patrol. In the spring of 1965, she conducted a similar patrol in European waters.
During the late winter and early spring of 1966, and again in the autumn, she was deployed for special operations. Following the completion of those assignments, her commanding officer received the Navy Commendation Medal for outstanding leadership, foresight, and professional skill. Other Scorpion officers and crewmen were cited for meritorious achievement. Scorpion is reputed to have entered an inland Russian sea during a "Northern Run" in 1966 where it successfully filmed a Soviet missile launch through its periscope before being forced to use its high speed to flee from Soviet Navy ships. Scorpion had a reputation for excellence and as a fast attack submarine it was a plum assignment for officers seeking to move up in a Navy in which submarine officers were gaining increasing clout.
At sometime prior to the "Med" deployment in 1968,Scorpion reportedly experienced an inoperable failure of the TDU (the abbreviation for the submarine's Trash Disposal Unit). As a result, it was prevented from underway elimination of food waste, metal cans, cardboard, etc. According to an on-board crewmember, this failure happened on the outbound leg of this at-sea period. As Scorpion approached Norfolk, the entire crew participated in physically removing the stored refuse, each man gathering up his the personal bag he'd used for the last 90 or more days, by tossing it over the side immediately following surfacing, rather than using proper disposal facilities a mere few miles away, the stinking contents having been held inside the hull for approximately ninety days. Can someone add a citation for this completely wobbly paragraph of shame.
On 1 February 1967 Scorpion entered the Norfolk Naval Shipyard for another extended overhaul. However, instead of the much-needed complete overhaul, she received only emergency repairs to get her back on duty as soon as possible. Operational pressures and complex and unforeseen problems created by the Submarine Safety Program (SUBSAFE) that was initiated after the 1963 loss of Thresher, meant that submarine overhauls went from nine months in length to 36 months. Intensive vetting of submarine component quality required by the SUBSAFE program coupled with various improvements and intensified structural inspections–particularly hull welding inspections using ultrasonic testing–were issues that reduced the availability of critical parts such as seawater piping. Cold War pressures prompted U.S. Submarine Fleet Atlantic (SUBLANT) officers to hunt for ways to reduce overhaul durations. The cost of that last overhaul was nearly one-seventh of those given other nuclear submarines at the same time. This was the result of concerns about the "high percentage of time offline" of nuclear attack submarines which was estimated to be at about 40% of total available duty time.
As Scorpion's original "full overhaul" was whittled down in scope, it was decided it would not receive long-overdue SUBSAFE work. Scorpion would not receive a new, central valve control system; in the event of an emergency, her crew would have to scramble around the engine room to find and manually operate large valves. Crucially, Scorpion would not receive a fix for the same emergency system that did not work on Thresher, the submarine whose loss was the reason for the existence of the SUBSAFE program. On that sub a pipe leak at depth prompted an emergency shutdown of the submarine's nuclear reactor; powerless, Thresher could still have surfaced if the Emergency Main Ballast Tank blow system worked. It did not. (Later, dockside tests on Thresher's sister sub Tinosa proved that the EMBT system did not work at test depth; moisture in the high-pressure air flasks froze in in-line strainers as the ballast tanks were blown.) Following a dispute between Charleston Naval Ship Yard, which claimed the EMBT system worked as-is, and SUBLANT, which claimed it did not, the EMBT was "tagged out" or listed as unusable. The aforementioned problems with overhaul duration, that saw Scorpion selected for a reduced experimental overhaul program, also caused all SUBSAFE work to be delayed as well during 1967.
The reduced overhaul concept Scorpion went through had been approved by Admiral David Lamar McDonald, the Chief of Naval Operations on 17 June 1966. On 20 July, McDonald also allowed deferral of the SUBSAFE extensions, which had otherwise been deemed essential since 1963.
During Scorpion's last six months of operational life, at least two sailors, Electrician's Mate Second Class Daniel Rogers and Radioman Chief Daniel Pettey, struggled to be released from duty aboard Scorpion due to the bad morale problems they witnessed. Rogers sought disqualification from submarine duty–which was then allowed–while Pettey attempted to transfer to the U.S. Army only to be released from Scorpion while in the Mediterranean just months before it was lost.
In late October 1967, Scorpion started refresher training and weapons system acceptance tests, and was given a new Commanding Officer, Francis Slattery. Following type training out of Norfolk, Virginia, she got underway on 15 February 1968 for a Mediterranean Sea deployment. She operated with the 6th Fleet into May and then headed west for home. Scorpion suffered several mechanical malfunctions including a chronic problem with Freon leakage from refrigeration systems. An electrical fire occurred in an escape trunk when a water leak shorted out a shore power connection.
Upon departing the Mediterranean on 16 May, two men departed Scorpion at Rota, Spain. One man left due to a family emergency, while the other, PO1 Joseph Underwood, departed for health reasons. Scorpion was then detailed to observe Soviet naval activities in the Atlantic in the vicinity of the Azores. With this completed, Scorpion prepared to head back to Naval Station Norfolk.
For an unusually long period of time, beginning shortly before midnight on 20 May and ending after midnight 21 May, Scorpion was attempting to send radio traffic to Naval Station Rota in Spain but was only able to reach a Navy communications station in Nea Makri, Greece, which forwarded Scorpion's messages to SUBLANT. Six days later, she was reported overdue at Norfolk. Navy personnel suspected possible failure and launched a search.
The search 
A public search was initiated, but without immediate success and on 5 June, Scorpion and her crew were declared "presumed lost." Her name was struck from the Naval Vessel Register on 30 June. Some reports indicate that a large and secret search was launched three days before Scorpion was expected back from patrol; this, combined with other declassified information leads to speculation that the US Navy knew of the Scorpion's destruction before the public search was launched.
The public search continued with a team of mathematical consultants led by Dr. John Craven, the Chief Scientist of the U.S. Navy's Special Projects Division. They employed the methods of Bayesian search theory, initially developed during the search for a hydrogen bomb lost off the coast of Palomares, Spain, in January 1966 in the Palomares B-52 crash. At the end of October, the Navy's oceanographic research ship, Mizar, located sections of the hull of Scorpion in more than 3,000 m (9,800 ft) of water about 740 km (400 nmi; 460 mi) southwest of the Azores. This was after the Navy had released sound tapes from its underwater "SOSUS" listening system which contained the sounds of the destruction of Scorpion. Subsequently, the Court of Inquiry was reconvened, and other vessels, including the bathyscaphe Trieste II, were dispatched to the scene, collecting many pictures and other data.
Although Dr. Craven received much credit for locating the wreckage of Scorpion, Gordon Hamilton—an acoustics expert who pioneered the use of hydroacoustics to pinpoint Polaris missile splashdown locations—was instrumental not only in acquiring the acoustic signals that were used in locating the vessel, but also in analyzing those signals to provide a compact "search box" wherein the wreck of Scorpion was finally located. Hamilton had established a listening station in the Canary Islands, which obtained a clear signal of what some scientists believe was the noise of the vessel's pressure hull imploding as she passed below crush depth. A little-known Naval Research Laboratory scientist named Chester "Buck" Buchanan, using a towed camera sled of his own design aboard Mizar, finally located Scorpion after nearly six months of searching. The towed camera sled, which was fabricated by J.L. "Jac" Hamm of Naval Research Laboratory's Engineering Services Division, is currently housed in the U.S. Navy Museum, Washington Navy Yard, Washington, DC. (Buchanan had located the wrecked hull of Thresher in 1964 using this same technique.)
It would appear that the bow of Scorpion skidded upon impact with the globigerina ooze on the seafloor, digging a sizable trench which created a significant hazard for the Trieste II crews attempting to maneuver close to acquire photographs and assess the wreckage with their own eyes. Much of the operations compartment had disappeared, and most of the debris field was identified as coming from the operations compartment. The sail had been dislodged as the hull of the operations compartment upon which it perched disintegrated, and was lying on its port side. One of Scorpion's running lights was in the open position as if it had been on the surface at the time of the mishap, although it may have been left in the open position during the vessel's recent nighttime stop at Rota. One Trieste II pilot who dived on Scorpion said the shock of the implosion may have knocked the light into the open position.
The aft section of the engine room had telescoped forward into the larger-diameter hull section.
Observed damage 
The secondary Navy investigation – using extensive photographic, video, and eyewitness inspections of the wreckage in 1969 – offered the opinion that Scorpion's hull was crushed by implosion forces as it sank below crush depth. The Structural Analysis Group, which included Naval Ships Systems Command's Submarine Structures director Peter Palermo, plainly saw that the torpedo room was intact, though it had been pinched from the operations compartment by massive hydrostatic pressure. The operations compartment itself was largely obliterated by sea pressure and the engine room had telescoped 50 ft (15 m) forward into the hull by collapse pressure, when the cone-to-cylinder transition junction failed between the auxiliary machine space and the engine room.
The only damage to the torpedo room compartment appeared to be a hatch missing from the forward escape trunk; Palermo pointed out that this would have occurred when water pressure entered the torpedo room at the moment of implosion. He also pointed out that the aft escape trunk hatch was open and the fairing was slightly dislodged, though it was still on its hinges. This conclusion was drawn by Palermo eighteen years after Scorpion was lost, when he reviewed new and extremely clear images taken by Jason Junior and Alvin as part of a Navy-Woods Hole Oceanographic Institution survey of Scorpion's wreck site.
Palermo could not rule out sabotage or collision as "plausible" causes of destruction. Palermo writes that the position of the masts and other evidence possibly indicate Scorpion was near the surface "just prior to sinking." However, other analysis in the COI concludes the damage to masts, antennas, and hoists is mere consequential damage from detachment of the sail and parting of the hydraulic piping. Palermo admits that a precursor signal that occurred some 22 minutes prior to the acoustic train left by the sinking "could have been the results of an internal explosion." He further states that "some of the remaining 14 acoustic events do have some of the characteristics of explosions," though he qualifies this by writing that such characteristics "may" also be attributed to other sources.
The submersible Alvin did take pictures of the inboard end of the propulsion shaft in 1986. However, the Navy kept this classified for many years and only recently revealed its existence. The picture shows that the locking lip has is gone. This lip was required to keep the shaft connected to the drive train in the bolted coupling. Cracking or shear of this lip is the root cause of the detachment of the shaft.
Acoustic evidence 
An extensive, year-long analysis of Gordon Hamilton's hydroacoustic signals of the submarine's demise was conducted by Robert Price, Ermine (Meri) Christian and Peter Sherman of the Naval Ordnance Laboratory. All three physicists were experts on undersea explosions, their sound signatures and destructive effects. Price was also an open critic of Dr. Craven. Their opinion, presented to the Navy as part of the Phase II investigation, was that the death noises likely occurred at 2,000 ft (610 m) when the hull failed. Fragments then continued in a free fall for another 9,000 ft (2,700 m). This appears to differ from conclusions drawn by Dr. Craven and Hamilton, who pursued an independent set of experiments as part of the same Phase II probe, demonstrating that alternate interpretations of the hydroacoustic signals were possibly based on the submarine's depth at the time it was stricken and other operational conditions. The Structural Analysis Group (SAG) findings argue an explosive event is unlikely, and are highly dismissive of Craven and Hamilton's tests. The SAG physicists argued that the absence of a bubble pulse, which invariably occurs in an underwater explosion, is absolute evidence that no torpedo explosion occurred outside or inside the hull of the Scorpion. It should also be pointed out that the massive hull of the Russian submarine Kursk emitted a huge bubble pulse when its torpedoes detonated at the time of its loss on 12 Aug 2000. Craven had attempted to prove Scorpion's hull could "swallow" the bubble pulse of a torpedo detonation by having Gordon Hamilton detonate small charges next to steel, air-filled containers. The real-world example of the Kursk which was ripped open by hydrogen peroxide-fueled torpedoes, had a pressure hull twice the size of Scorpion's, handily indicating even its massive and strong hull could not absorb the bubble pulse since its own bubble pulse signal exited its hull and was transmitted to geophones across Europe.
The 1970 Naval Ordnance "Letter", the intensive acoustics study of Scorpion destruction sounds by Price and Christian, was a supporting study within the SAG report. In its Conclusions and Recommendations section, the NOL acoustic study states:
The first SCORPION acoustic event was not caused by a large explosion, either internal or external to the hull. The probable depth of occurrence...and the spectral characteristics of the signal support this. In fact, it is unlikely that any of the Scorpion acoustic events were caused by explosions.
The Naval Ordnance Laboratory based much of its findings on an extensive acoustic analysis of the torpedoing and sinking of Sterlet in the Pacific in early 1969, seeking to compare its acoustic signals to those generated by Scorpion. Price, a critic of Craven and Hamilton's analysis of the sounds emitted by Scorpion, found the Navy's scheduled sinking of Sterlet fortuitous. Nonetheless, Sterlet was a small World War II-era diesel-electric submarine of a vastly different design and construction from Scorpion with regard to its pressure hull and other characteristics. Its sinking resulted in three identifiable acoustic signals as compared to Scorpion's 15, something Price could not adequately explain. The mathematical calculations Price used to arrive at his analysis–and dispute some of Craven and Hamilton's conclusions–remain unknown to the public.
When completed, the NOL acoustics study of Sterlet and Scorpion sinking sounds provided a highly debated explanation as to how Scorpion may have reached its crush depth by anecdotally referring to the uncontrolled and nearly fatal dive of the diesel submarine Chopper in January 1969:
Piecing together all the information (or suggestions) we can glean from the analysis of the hydroacoustic data, the photographs of the wreckage of SCORPION and THRESHER, and the results of the STERLET acoustic measurements, we believe the sequence of occurrences outlined below is a plausible description of what might have happened when Scorpion sank. 6.1 (Redacted) SOME UNKNOWN INCIDENT OR CHAIN OF INCIDENTS CAUSED THE SCORPION TO SINK OUT OF CONTROL. The February 1969 USS Chopper (SS-342) mishap is an example of loss of electrical power in a submarine. It was followed by corrective action, initiation of which was delayed almost to the fatal limit by a combination of failures. Fortunately the plunge of the ship towards the bottom was halted (redacted) just before the hull reached collapse depth and the ship was able to surface, though not under control and with some damage caused by excessive pressure.
In the same May 2003 N77 letter excerpted above (see 1. with regard to the Navy's view of a forward explosion), however, the following statement appears to dismiss the NOL theory, and again unequivocally point the finger toward an explosion forward:
The Navy has extensively investigated the loss of Scorpion through the initial court of inquiry and the 1970 and 1987 reviews by the Structural Analysis Group. Nothing in those investigations caused the Navy to change its conclusion that an unexplained catastrophic event occurred.
At the time of her sinking, there were 99 crewmen aboard Scorpion. The boat contained highly sophisticated spy gear and spy manuals, two nuclear-tipped torpedoes, and a nuclear propulsion system. The best available evidence indicates that Scorpion sank in the Atlantic Ocean on 22 May 1968 at approximately 1844Z (Zulu time; see UTC) while in transit across the Atlantic Ocean from Gibraltar to her home port at Norfolk, Virginia.
Several hypotheses about the cause of the loss have been advanced. Some have suggested that hostile action by a Soviet submarine caused Scorpion's loss. Shortly after her sinking, the Navy assembled a Court of Inquiry to investigate the incident and to publish a report about the likely causes for the sinking. The court was presided over by Vice Admiral Bernard Austin, who had presided over the inquiry into the loss of Thresher. The panel's conclusions, first printed in 1968, were largely classified. At the time, the Navy quoted frequently from a portion of the 1968 report that said no one is likely ever to "conclusively" determine the cause of the loss. The Clinton administration declassified most of this report in 1993, and it was then that the public first learned that the panel considered that a possible cause was the malfunction of one of Scorpion's own torpedoes. (The panel qualified its opinion, saying the evidence it had available could not lead to a conclusive finding about the cause of her sinking.) However, the Court of Inquiry did not reconvene after the 1969 Phase II investigation, and did not take testimony from a group of submarine designers, engineers and physicists who spent nearly a year evaluating the data.
Present location 
Today, the wreck of Scorpion is reported to be resting on a sandy seabed at the bottom of the Atlantic Ocean in approximately 3,000 m (9,800 ft) of water. The site is reported to be approximately 400 nmi (740 km) southwest of the Azores Islands, on the eastern edge of the Sargasso Sea. The actual position is 32°54.9'N, 33°08.89'W. The U.S. Navy has acknowledged that it periodically visits the site to conduct testing for the release of nuclear materials from the nuclear reactor or the two nuclear weapons aboard her, and to determine whether the wreckage has been disturbed. The Navy has not released any information about the status of the wreckage, except for a few photographs taken of the wreckage in 1968, and again in 1985 by deep water submersibles.
The Navy has also released information about the nuclear testing performed in and around the Scorpion site. The Navy reports no significant release of nuclear material from the sub. The 1985 photos were taken by a team of oceanographers working for the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts.
Environmental monitoring 
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. nuclear-powered ships and boats. The reports provide specifics on the environmental sampling of sediment, water, and marine life that is done to ascertain whether the submarine has significantly affected the deep-ocean environment. The reports also explain the methodology for conducting this deep sea monitoring from both surface vessels and submersibles. The monitoring data confirm that there has been no significant effect on the environment. The nuclear fuel aboard the submarine remains intact and no uranium in excess of levels expected from the fallout from past atmospheric testing of nuclear weapons has been detected by the Navy's inspections. In addition, Scorpion carried two nuclear-tipped Mark 45 anti-submarine torpedoes (ASTOR) when she was lost. The warheads of these torpedoes are part of the environmental concern. The most likely scenario is that the plutonium and uranium cores of these weapons corroded to a heavy, insoluble material soon after the sinking, and they remain at or close to their original location inside the torpedo room of the boat. If the corroded materials were released outside the submarine, their large specific gravity and insolubility would cause them to settle down into the sediment.
Shaft detachment 
Very little has ever been documented on why the propulsion shaft is out of the boat. The 29 foot long shaft and its attached propeller lie in the debris field.
There is a mechanical hub and bolt coupling arrangement that holds the shaft in place and connects it to the drive flange of the ship's propulsion system. This coupling is of rigid design and does not tolerate flexing forces. The picture of the shaft end clearly shows that the locking lip is gone from the major diameter of the shaft end. This ligament is very susceptible to fatigue failure and crack propagation along its root. Such a structural failure will release the shaft from the coupling.
Shaft detachment was discussed briefly by the COI, but the opinion suggests it was not an iniating cause; no analysis to support the supposition was ever recorded.
Unsubstantiated theories about the loss 
Accidental activation of torpedo 
The US Navy's Court of Inquiry listed as one possibility the inadvertent activation of a battery-powered Mark 37 torpedo. This acoustic homing torpedo, in a fully ready condition and without a propeller guard, is believed by some to have started running within the tube. Released from the tube, the torpedo then somehow became fully armed and successfully engaged its nearest target—Scorpion herself. This is considered highly unlikely due to the fact that Scorpion would have maintained the ability to destroy the weapon before it reengaged. Although much has been made of claims by Dr. Craven that the SOSUS network tracked the submarine moving back onto its original course, which would be consistent with performing a 360° turn in an attempt to activate a torpedo's safety systems, Gordon Hamilton has said that the acoustical data is too garbled to reveal any such details.
However, much is overlooked in entertaining Craven's guesswork. The fact that SOSUS did not track Scorpion and no change in course was ever detectable by any acoustic information. Bruce Rule proved this conclusively by analyzing the time differences in noise events. Bruce proves that the noises were all post collapse. In other words, Craven had no data to support his claim and he was informed of his errors on 18 July 1968 at 9.30pm. He has not changed his story despite the facts.
Another problem with the torpedo theory is that numerous safeguards are in place that would enable the torpedomen to disable the warhead if it were launched and its anti-circular run switch also failed, allowing it to strike its mother ship without detonating, in which case the weapon would thud harmlessly off the hull. Few torpedomen familiar with the Mark 37 have expressed confidence in the self-destruction-by-torpedo theory.
A more fundamental failure of the torpedo theory is that there is no explosive damage anywhere in the wreck. The Mk37 torpedo had a very small warhead and was designed to home in on noise of propellers of ships. The explosion would have been too small to take down a hull like 589. But the most obvious failure of the torpedo theory, is that there are no remnants of the torpedo in the debris field. If it was a torpedo the remains of the weapon would be in the debris field, which was extensively photographed to the point rifle cartridges are identified.
Explosion of torpedo 
A later theory was that a torpedo may have exploded in the tube, caused by an uncontrollable fire in the torpedo room. The book Blind Man's Bluff documents findings and investigation by Dr. John Craven, who surmised that a likely cause could have been the overheating of a faulty battery. (Dr. Craven later stated in the book Silent Steel that he was misquoted.) The Mark 46 silver-zinc battery used in the Mark 37 torpedo had a tendency to overheat, and in extreme cases could cause a fire that was strong enough to cause a low-order detonation of the warhead. If such a detonation had occurred, it might have opened the boat's large torpedo-loading hatch and caused Scorpion to flood and sink. However, while Mark 46 batteries have been known to generate so much heat that the torpedo casings blistered, none is known to have damaged a boat or caused an explosion.
Dr. John Craven mentions that he did not work on the Mark 37 torpedo's propulsion system and only became aware of the possibility of a battery explosion twenty years after the loss of Scorpion. In his book The Silent War, he recounts running a simulation with former Scorpion Executive officer Lieutenant Commander Robert Fountain, Jr. commanding the simulator. Fountain was told he was headed home at 18 knots (33 km/h) at a depth of his choice, then there was an alarm of "hot running torpedo". Fountain responded with "right full rudder", a quick turn that would activate a safety device and keep the torpedo from arming. Then an explosion in the torpedo room was introduced into the simulation. Fountain ordered emergency procedures to surface the boat, stated Dr. Craven, "but instead she continued to plummet, reaching collapse depth and imploding in ninety seconds—one second shy of the acoustic record of the actual event."
Craven, who was the Chief Scientist of the Navy's Special Projects Office, which had management responsibility for the design, development, construction, operational test and evaluation and maintenance of the UGM-27 Polaris Fleet Missile System had long believed Scorpion was struck by her own torpedo, but revised his views during the mid-1990s when engineers testing Mark 46 batteries at Keyport, Washington, said the batteries leaked electrolyte and sometimes burned while outside of their casings during lifetime shock, heat and cold testing. Although the battery manufacturer was accused of building bad batteries, it was later able to successfully prove its batteries were no more prone to failure than those made by other manufacturers.
Malfunction of trash disposal unit 
During the 1968 inquiry, Vice Admiral Arnold F. Shade testified that he believed that a malfunction of the trash disposal unit (TDU) was the trigger for the disaster. Shade theorized that the sub was flooded when the TDU was operated at periscope depth and that other subsequent failures of material or personnel while dealing with the TDU-induced flooding led to the sub's demise.
Soviet attack 
The book All Hands Down by Kenneth Sewell and Jerome Preisler (Simon and Schuster, 2008) concludes that the Scorpion was destroyed while en route to gather intelligence on a Soviet naval group conducting operations in the Atlantic.  While the mission for which the submarine was diverted from her original course back to her homeport is a matter of record, its details remain classified.
Ed Offley's book, Scorpion Down, promotes a hypothesis suggesting that the Scorpion was sunk by a Soviet submarine during a standoff that started days before 22 May. Offley also cites that it occurred roughly at the time of the submarine's intelligence-gathering mission, from which she was redirected from her original heading for home; according to Offley, the flotilla had just been harassed by another US submarine, the USS Haddo. 
Both All Hands Down' and Scorpion Down point toward involvement by the KGB spy-ring (the so-called Walker Spy-Ring) led by John Anthony Walker, Jr. in the heart of the US Navy's communications, stating that it could have known that the Scorpion was coming to investigate the Soviet flotilla. According to this theory, there was a common agreement made by both navies to hide the truth about both incidents. Several USN SSNs collided with Soviet Echo subs in Russian and Scottish waters in this period.
However, all good sea stories like the books above, are rarely accurate. The Soviet submarine force was as professional as the British and the Americans. Moscow never issued a 'fire' command during the cold war. The sensational plots of the named novels were not supported by the deployed Soviet weaponry of the day. It is also known fact that there was not another ship within 200 miles of Scorpion at the time of the sinking
The results of the U.S. Navy's various investigations into the loss of Scorpion are inconclusive. While the Court of Inquiry never endorsed Dr. Craven's torpedo theory regarding the loss of Scorpion, its Findings of Facts released in 1993 carried Craven's torpedo theory at the head of a list of possible causes of Scorpion's loss.
The Navy failed to inform the public that both the U.S. Submarine Force Atlantic and the Commander-in-Chief U.S. Atlantic Fleet opposed Craven's torpedo theory as unfounded and also failed to disclose that a second technical investigation into the loss of Scorpion completed in 1970 actually repudiated claims that a torpedo detonation played a role in the loss of Scorpion. Despite the second technical investigation, the Navy continues to attach strong credence to Craven's view that an explosion destroyed her, as is evidenced by this excerpt from a May 2003 letter from the Navy's Submarine Warfare Division (N77), specifically written by Admiral P.F. Sullivan on behalf of Vice Admiral John J. Grossenbacher (Commander Naval Submarine Forces), the Naval Sea Systems Command, Naval Reactors, and others in the US Navy regarding its view of alternative sinking theories:
The first cataclysmic event was of such magnitude that the only possible conclusion is that a cataclysmic event (explosion) occurred resulting in uncontrolled flooding (most likely the forward compartments).
Some erroneously claim Grossenbacher's (and Sullivan's) determination is drawn solely from the inconclusive Findings of Fact, generated by the US Navy's Court of Inquiry into Scorpion sinking. This is untrue, as their letter explicitly mentions their review of a secondary study by the Structural Analysis Group in 1970, and a later report by Dr. Robert Ballard, whose investigative team visited the Scorpion wreck in 1985 using the search for Titanic as a cover since the visit was part of a recently declassified mission to visit Scorpion as well as Thresher, another nuclear sub which was lost off the coast of Cape Cod, Massachusetts.
However, even Admirals get technical details twisted about and confused. The letters referred to above were not written by the Admirals themselves, but well meaning but unknowing staffers who just cut and pasted parts of the dusty files to make a response consistent with the belief of the day. In reality, there is an excellent analysis of the acoustic events by Bruce Rule in his book Why the USS Scorpion (SSN 589) Was Lost: The Death of a Submarine in the North Atlantic.
It is quite clear in the Rule's analysis that the first event was the sound of a hull being crushed in the deep ocean. The magnitude is consistent with the collapse and not with any initiating explosion as penned by the Admiral's staffer.
The Unexplained 
For all the guess work and possibilities considered in the investigation, some items were never explained. The reported sighting of a sailor on the ocean floor near the wreck was greatly discussed, but never analyzed. The sketch by Trieste pilots was included in a report as an appendix with little discussion.
See also 
- Submarines destroyed by hot-running torpedoes: HMS Sidon and K-141 Kursk.
- USS George Washington (SSBN-598) was originally to have been Scorpion (SSN-589), and began construction under that name. Before completion it was heavily modified into the first SSBN Ballistic Missile Submarine, with the addition of large hull section housing 16 Polaris A-1 missiles.
- Project Azorian, which attempted to raise Soviet submarine K-129 (1960) in 1974. K-129 had sunk 2.5 months prior to Scorpion, on 8 March 1968.
- CINCLANTFLEET History Log June '68 to July '69 page 104 at 4.a.
- Sherry Sontag and Christopher Drew, Blind Man's Bluff: The Untold Story of American Submarine Espionage (New York: Harper Paperbacks, 2000), p. 432.
- "Submarine vets call for USS Scorpion investigation". Usatoday.com. 22 May 1968. Retrieved 2012-11-16.
- Ed Offley, Scorpion Down: Sunk by the Soviets, Buried by the Pentagon: The Untold Story of the USS Scorpion (New York: Perseus Books Group, 2007), pp. 241 ff. ISBN 978-0-465-00884-1.
- "Strange Devices That Found the Sunken Sub Scorpion." Popular Mechanics, April 1969, pp. 66–71.
- Command History of the Commander in Chief U.S. Atlantic Fleet, OPNAV REPORT 5750-1, July '68 - June '69, p. 104 at 4. a.
- 'Evaluation of Data and Artifacts Related to USS Scorpion (SSN 589)', 29 June 1970, Palermo, Jackson, Sachse, et. al. Structural Analysis Group, page 5.14, section 5.3.3 Specific Items of Debris
- COI Opinion 4.o. p254 http://www.jag.navy.mil/library/investigations/USS%20SCORPAIN%2027%20MAY%2068.pdf
- Why The USS SCORPION (SSN-589) Was Lost, Bruce Rule, page last of Chapter 1, Analysis. http://www.amazon.com/Why-USS-Scorpion-SSN-Lost/dp/1608881202/ref=sr_1_1?ie=UTF8&qid=1365620878&sr=8-1&keywords=bruce+rule
- Why The USS SCORPION (SSN-589) Was Lost, Bruce Rule, page last of Chapter 1, calc sheet, http://www.amazon.com/Why-USS-Scorpion-SSN-Lost/dp/1608881202/ref=sr_1_1?ie=UTF8&qid=1365620878&sr=8-1&keywords=bruce+rule
- Sontag and Drew, Blind Man's Bluff, 432.
- Stephen Johnson, Silent Steel: The Mysterious Death of the Nuclear Attack Sub USS Scorpion(Hoboken, NJ: John Wiley & Sons, 2006), p. 304.
- Johnson, Stephen (23 May 1993). "A long and deep mystery/Scorpion crewman says sub's '68 sinking was preventable". Houston Chronicle (Hearst Corporation). Retrieved 27 June 2008.
- Kenneth Sewell and Jerome Preisler. All Hands Down: The True Story of the Soviet Attack on the USS Scorpion (New York: Simon & Schuster, 2008), p. 288.
- Ed Offley, Scorpion Down: Sunk by the Soviets, Buried by the Pentagon: The Untold Story of the USS Scorpion (New York: Perseus Books Group, 2007), p. 480.
- Court of inquiry, finding of fact #49 to 53, see http://www.jag.navy.mil/library/investigations/USS%20SCORPAIN%2027%20MAY%2068.pdf
- Evaluation of Data and Artifacts Related to USS Scorpion (SSN 589), Palermo, et. al., 29 June 1970, p7.11, Exhibit 7-2
Further reading 
- Robert W. Love. History of the U.S. Navy, 1942–1991 (History of the U.S. Navy) (October 1992 ed.). Stackpole Books. p. 912. ISBN 0-8117-1863-8.
- Kenneth Sewell, Clint Richmond. Red Star Rogue: The Untold Story of a Soviet Submarine's Nuclear Strike Attempt on the U.S. (26 September 2006 ed.). Pocket Star. p. 480. ISBN 1-4165-2733-8.
- Bruce Rule. Why the USS Scorpion (SSN 589) Was Lost: The Death of a Submarine in the North Atlantic (31 October 2011 ed.). Nimble Books LLC. p. 74. ISBN 1608881202.
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