USS Thresher (SSN-593)
 USS Thresher (SSN-593) | |
| Career | 
|
|---|---|
| Ordered: | 15 January 1958 |
| Keel laid: | 28 May 1958 |
| Launched: | 9 July 1960 |
| Commissioned: | 3 August 1961 |
| Fate: | Lost during deep diving tests, 10 April 1963 |
| Stricken from US Navy's ship rolls: | 16 April 1963 |
| General characteristics | |
| Displacement: | 3540 tons light, 3770 tons submerged |
| Length: | 279 ft (85 m) |
| Beam: | 32 ft (9.7 m) |
| Draft: | 26 ft (8.7 m) |
| Propulsion: | 1 Westinghouse S5W PWR, Westinghouse Geared Turbines 15,000 shp (11 MW) |
| Speed: | 20+ knots (37 km/h) |
| Complement: | 16 officers, 96 men |
| Armament: | Four 21 inch (533 mm) torpedo tubes amidships |
| Motto: | Vis Tacita (Silent Strength) |
The second USS Thresher (SSN-593) was the lead ship of its 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.
She was named for the Thresher Shark, harmless to man, and easily recognizable because its tail is longer than the combined length of its body and head.
The contract to build the 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 Burdett Warder, and was commissioned on 3 August 1961, with Commander Dean L. Axene in command.
Early career
Thresher conducted lengthy sea trials in the western Atlantic and Caribbean Sea areas in 1961 and 1962. These tests provided a thorough evaluation of her many new and complex technological features and weapons. Following these trials, she took part in Nuclear Submarine Exercise (NUSUBEX) 3-61 off the northeastern coast of the United States from September 18 to September 24, 1961.
On October 18 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 reached criticality. With no electrical power for ventilation, temperatures in the machinery spaces reached 60 °C (140 °F), and the boat was partially evacuated. Cavalla (SS-244) arrived the next morning and provided power from her diesel engines, enabling Thresher to restart her reactor. [1]
Thresher conducted further trials and fired test torpedoes before returning to Portsmouth on November 29. 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, the 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 mooring 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, the ship returned south for more tests and trials off Key West, Florida. Thresher then returned northward and remained in dockyard for refurbishment through the early spring of 1963.
Loss
On April 9, 1963, after the completion of this work, Thresher, now commanded by LCDR John Wesley Harvey, began post-overhaul trials. Accompanied by the submarine rescue ship USS Skylark (ASR-20), she sailed to an area some 350 km (220 miles) east of Cape Cod, Massachusetts, and on the morning of April 10 started deep-diving tests. As these proceeded, garbled communications were received over the underwater telephone by Skylark, indicating that after initial problems Thresher had tilted and the crew were attempting to regain control. A few words were understandable, including the famous final phrase "... minor difficulties, have positive up-angle, attempting to blow." [1] [2] [3] When the garbled communications --- which were followed by the ominous sound of pressurized air escaping --- eventually ceased, surface observers gradually realized that Thresher had sunk. All 129 officers, crewmen and military and civilian technicians aboard her were lost.
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 feet (2560 m) below the surface, in six major sections. The majority of the debris is in an area of about 134,000 m² (160,000 yd²). The major sections are the sail (the raised tower atop a submarine's main deck), sonar dome, bow section, engineering spaces section, operations spaces section, and the tail section.
Deep sea photography, recovered artifacts, and an evaluation of her design and operational history permitted a Court of Inquiry to conclude that the Thresher had probably sunk due to the failure of a weld 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 to not 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, causing a subsequent loss of propulsion. The inability to blow water from the ballast tanks was later attributed to excessive moisture in Threshers high-pressure air flasks, which froze and plugged its own flowpath while passing through the blow valves. This was later simulated in dock-side tests on the 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.
Unlike diesel submarines, nuclear subs relied on speed and deck angle (that is, driving the ship towards the surface) rather than deballasting to surface. Ballast tanks were almost never blown at depth; this 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 that 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 that provided propulsion and electricity. This was done to prevent an over-rapid cooldown of the reactor, which could actually restart spontaneously and go out of control if the core was cooled too quickly. Thresher's Main Propulsion Assistant, Lt. Cdr. 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 freak household accident -- he had been all but ordered ashore by a sympathetic Commander Harvery. 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. In later life, McCoole was sure that 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 procedures, allowing steam to be withdrawn from the secondary system in limited quantities for several minutes following a scram.
There was much (covert) criticism of Rickover's training after Thresher went down, the argument being that his "nukes" were so well conditioned to protect the nuclear plant that they would have shut the main steam stop valves by rote -- depriving the ship of needed propulsion -- even at great depths and with the ship clearly in jeopardy. Nothing enraged Rickover more than this argument. Common sense, he argued, would prove this to be untrue.
It's more likely that the engine room crew was simply overwhelmed by the flooding casualty, or took too long to contain it. In a dockside simulation of flooding in the engineroom, held before Thresher sailed, it took the watch in charge 20 minutes to isolate a simulated leak in the auxiliary seawater system. At test depth, taking on water, and with the reactor shut down, Thresher would not have had anything like 20 minutes to recover. Even after isolating a short-circuit in the reactor controls it would have taken nearly 10 minutes to restart the plant.
Thresher imploded (that is, one or more of her compartments collapsed inwards in a fraction of a second) at a depth somewhere between 1,300 feet and 2,000 feet. Those not injured by the flooding would have died in a split second.
Over the next several years, the Navy implemented the SUBSAFE program to correct design and construction problems on all submarines (nuclear and diesel-electric) in service, under construction, and in planning. It was discovered during the formal inquiry that record-keeping at the Portsmouth Naval Shipyard was far from adequate. For example, no one could determine the whereabouts of hull weld X-rays made of Thresher's sister ship Tinosa, nearing completion at Portsmouth, or, indeed, whether they had been made at all. It was also determined that Thresher 's engine room layout was awkward, and in fact dangerous, as there were no centrally-located isolation valves for the main and auxiliary seawater systems. Most subs were subsequently equipped or retrofitted with so-called "chicken switches", which allowed the Engineer Officer of the Watch in the maneuvering room to remotely close isolation valves in the seawater systems from a central panel, a task that would have had to be performed manually on Thresher. It's worth noting that such valves might not have been reachable during Thresher's presumed flooding casualty: at such deep depths, the blast of water from even a small leak can dent metal cabinets, rip insulation from cables, and, in the case of a large break, split a man in half. (Water pressure at 1,000 feet is about 450 pounds to the square inch.)
Apart from Scorpion, the U.S. Navy has suffered no further losses of nuclear submarines.
The Navy has periodically monitored the environmental conditions of the site since the sinking and 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 the submarine 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.
Details of the disaster
- 7:47 AM: Thresher begins its descent to the test depth of 1300 feet.
- 7:52 AM: Thresher levels off at 400 feet, contacts the surface, and the crew inspects the ship for leaks. None are found.
- 8:09 AM: Commander Harvey reports reaching half the test depth.
- 8:25 AM: Thresher reaches 1000 feet depth.
- 9:02 AM: 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.) Commander Harvey orders a course change: "Twenty degrees right rudder and five degrees down angle."
- 9:09 AM: It is believed that a brazed pipe-joint ruptures in the engine room. The crew attempts to stop the leak while the room is filled with a cloud of mist. Harvey orders full speed, upward tilt of 15 degrees, and emptying the main ballast tank in order to surface. Due to Joule-Thomson effect, the pressurized air rapidly expanding in the pipes cools down, condensing moisture and depositing it on strainers installed in the system to protect the moving parts of the valves; in only a few seconds the moisture freezes, clogging the strainers and blocking the air flow, halting the effort to blow water out of the ballast tanks. The water leaking from the broken pipe most likely causes short circuits leading to an automatic shutdown of the ship's reactor. The vessel loses propulsion. Harvey orders propulsion shifted to a battery-powered backup system. Assuming that the flooding was contained quickly, the engine room crew begins to restart the reactor, an operation that is expected to take at least 7 minutes.
- 9:13 AM: Harvey reports status via underwater telephone. The transmission is garbled, though some words are recognizable: "We are experiencing minor difficulties, have positive up-angle, and are attempting to blow." The submarine, growing heavier from water flooding the engine room, continues its descent. Another attempt to empty the ballast tanks is performed, again failing due to the formation of ice.
- 9:15 AM: Skylark attempts to contact Thresher, gets no immediate answer.
- 9:16 AM: Garbled transmission received from Thresher.
- 9:17 AM: A second transmission is received, with somewhat recognizable phrase "exceeding test depth ... nine hundred north". The leak from the broken pipe grows with increased pressure.
- 9:18 AM: Skylark detects a high-energy low-frequency noise with characteristics of an implosion.
On April 11, at a news conference at 10:30 AM, the Navy officially concluded the ship lost.
Officers and men lost with USS Thresher (SSN-593)
The following crew members were lost with Thresher (SSN-593). NOTE: the designator "(SS)" after an enlisted man's name and rate denotes "Qualified in Submarines", and entitles the man to wear the coveted silver dolphin insignia.
Officers
Enlisted men
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Enlisted men (continued)
Naval observers
Civilian engineers and technicians
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See also
- Deep Submergence Rescue Vehicle
- USS Thresher for other ships of the same name
- USS Scorpion (SSN-589)
- John Craven USN Key individual in the search for Thresher
Footnotes
- ^ "COMSUBPAC Web site, Submarines Lost or Damaged before and after World War II". Retrieved 2006-02-02.
- ^ "U.S. Gov Info / Resources, US Navy's Submarine Rescue Team". Retrieved 2006-02-02.
- ^ "NOVA Web site, transcript of "Submarines, Secrets, and Spies"". Retrieved 2006-02-02.
References
- Loss of USS Thresher: http://www.submarinehistory.com/Thresher.html
- Thresher-Scorpion Memorial: http://www.submarinehistory.com/ThresherScorpionMemorial.html
- World War II National Submarine Memorial - West: http://www.submarinehistory.com/WWIISubmarineMemorial.html
- World War II National Submarine Memorial - East: http://www.submarinehistory.com/WWIISubmarineMemorial-East.html
- Sontag, Sherry; Drew, Christopher; Drew, Annette Lawrence (1998). Blind Man's Bluff: The Untold Story of American Submarine Espionage. Harper. ISBN 0-06-103004-X.
- Polmar, Norman "Death of the Thresher" The Lyons Press, ISBN 1-58574-348-8
- Bentley, John "The Thresher Disaster" Doubleday, ISBN 0-385-03057-6
- Rockwell, Theodore "The Rickover Effect" iUniverse, Inc, ISBN 0-595-74527-X
- http://archiver.rootsweb.com/th/read/USS-THRESHER-SSN593/2005-01/1104944120 -- McCoole's statement re: shutting main steam valves during reactor scram
- DeMercurio, Michael "The Complete Idiot's Guide to Submarines" Alpha Books, ISBN-13: 978-0028644714