Pacific Vortex: the Thresher, the Bluefin, the Scorpion

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"Most mysteries have a way of eventually getting solved. The Thresher, the Bluefin, the Scorpion - the Navy never gave up until everyone was found."

The Thresher

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

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

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

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

Off Charleston, SC, Thresher undertook operations observed by the Naval Antisubmarine Warfare Council before she returned briefly to New England waters, after which she proceeded to Florida 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, by the Electric Boat Company, Thresher went south for more tests and trials off Key West, Florida, then returned northward and remained in dockyard for refurbishment through the early spring of 1963.

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

After an extensive underwater search using the bathyscaphe Trieste, oceanographic ship Mizar and other ships, Thresher's remains were located on the sea floor, some 8,400 ft (2,600 m) below the surface, in six major sections. The majority of the debris had spread over an area of about 134,000 m2 (160,000 sq yd). The major sections were the sail, sonar dome, bow section, engineering spaces section, operations spaces section, and the stern planes.

Deep sea photography, recovered artifacts, and an evaluation of her design and operational history permitted a Court of Inquiry to conclude Thresher had probably suffered the failure of a joint in a salt water piping system, which relied heavily on silver brazing instead of welding; earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require a repair. High-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, which in turn caused a shutdown ("scram") of the reactor, with a subsequent loss of propulsion. The inability to blow the ballast tanks was later attributed to excessive moisture in the ship's high-pressure air flasks, which froze and plugged the flasks' flowpaths while passing through the valves.

This was later simulated in dock-side tests on Thresher's sister ship, Tinosa. During a test to simulate blowing ballast at or near test depth, ice formed on strainers installed in valves; the flow of air lasted only a few seconds. Air driers were later retrofitted to the high pressure air compressors, beginning with Tinosa, to permit the emergency blow system to operate properly.

Unlike diesel submarines, nuclear 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.

Thresher's Reactor Control Officer, Lieutenant Raymond McCoole, was not at his station in the maneuvering room, or indeed on the ship, during the fatal dive. McCoole was at home caring for his wife who had been injured in a household accident—he had been all but ordered ashore by a sympathetic Commander Harvey. McCoole's trainee, Jim Henry, fresh from nuclear power school, probably followed standard operating procedures and gave the order to isolate the steam system after the scram, even though Thresher was at or slightly below her maximum depth and was taking on water.

Once closed, the large steam system isolation valves could not be reopened quickly. Reflecting on the situation in later life, McCoole was sure he would have delayed shutting the valves, thus allowing the ship to "answer bells" and drive herself to the surface, despite the flooding in the engineering spaces. Admiral Rickover later changed the procedure, allowing steam to be withdrawn from the secondary system in limited quantities for several minutes following a scram.

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 1,300–2,000 ft (400–610 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, water, and marine life which were taken to ascertain whether Thresher's nuclear reactor has had a significant effect on the deep ocean environment. The reports also explain the methodology for conducting deep sea monitoring from both surface vessels and submersibles. The monitoring data confirms that there has been no significant effect on the environment. Nuclear fuel in the submarine remains intact.

According to newly declassified information, the Navy sent Commander (Dr.) Robert Ballard, the oceanographer credited for the successful search for the wreck of RMS Titanic, on a secret mission to map and collect visual data on both Thresher and Scorpion 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, Los Angeles-class boats are called "688s" because the hull number of USS Los Angeles was SSN-688. The Thresher-class boats should thus be called "593s", but since Thresher's sinking they have been referred to as "594s" (Permit class).

The Bluefin

There has never been a sub named the Bluefin

USS Scorpion

USS Scorpion (SSN-589) 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. Navy has lost, the other being USS Thresher (SSN-593), which sank on 10 April 1963 off the coast of New England.

Service historyScorpion'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.

[edit] 1960–1967Assigned 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, and, 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 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.

[edit] OverhaulOn 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 ship 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 ship 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 the Chief of Naval Operations on 17 June 1966. On 20 July, the CNO 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.

Loss
Disappearance
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 Base 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 recent reports now indicate that a large and secret search was launched three days before Scorpion was expected back from patrol; this combined with other declassified information led many to speculate 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.)

Wreckage
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 locked 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 appeared to have skidded sideways on impact, since it was less hydrodynamically efficient than the bullet-shaped torpedo room, which investigators believed would have developed a greater downward velocity. 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 smashed 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 sprung open and appeared twisted, 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." 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.

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 freefall for another 9,000 ft (2,700 m). This appears to differ with 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. Though the Structural Analysis Group (SAG) findings argue an explosive event is unlikely, and are highly dismissive of Craven and Hamilton's tests, they failed to present information that ruled out an explosive event.

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, 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.

Secrecy
At the time of her sinking, there were 99 crewmen aboard Scorpion. The boat contained a treasure-trove of 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 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 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 of the malfunction was 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 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. The circumstances of the Woods Hole mission show the high level of secrecy the Navy attaches to Scorpion; at the time the photographs were taken, the Navy and Woods Hole both maintained that the Woods Hole team was searching for the wreckage of the sunken ocean liner, Titanic. It was only after newspapers learned and reported that the Woods Hole team was also searching for Scorpion that the Navy admitted as much, and released some of the photographs taken during the expedition.

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.

Theories about the loss
The cause of her loss, to date, has not been fully confirmed by the USN and various possibilities have been raised.

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 180° 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.

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.

In Silent Steel, Fountain reveals he does not believe Scorpion was sunk by her own torpedo, and during the Court of Inquiry, physicists and engineers who carried out the simulations demanded by Dr. Craven testified that the massively complex simulations, using the crude computing power of the day, were of little value since they were so speculative. This testimony brought a rebuke from the court's members who were sufficiently persuaded by Craven's theories to list them foremost above all others. What has become apparent is that many investigators, even according to a Navy history of the investigation, were upset by Craven's devotion to his hot-running torpedo theory.

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–at the time of Scorpion's sinking the most technically advanced military system ever deployed–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. In fact, the batteries suspected of being unreliable were manufactured too late to have been installed in Scorpion's torpedoes.

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.

US Navy conclusions
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 the submarine.

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.

"We have a saying in the Navy about ships lost out here:

"Those who lie deep in the Atlantic Sea
Are recalled by shrines, wreaths and poetry.
But those who lie in the Pacific Sea
Lie forgotten for all eternity."

I've been unable to find any reference to this saying outside Clive Cussler's book!