Military Product Description
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, with Commander Dean L. Axene in command.
1 Early career
3 Details of the disaster
4 Officers and men lost with USS Thresher (SSN-593)
4.2 Enlisted men
4.3 Enlisted men (continued)
4.4 Naval observers
4.5 Civilian engineers and technicians
6 See also
9 External links
 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 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 (SS-244) 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 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, 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 April 9, 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 USS Skylark (ASR-20), she sailed to an area some 350 kilometers (220 statute miles or 190 nautical miles) east of Cape Cod, Massachusetts, and on the morning of April 10 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's queries as to if Thresher were under control were answered only by the ominous sound of compartments collapsing, surface observers gradually realized 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 m˛ (160,000 yd˛). The major sections are 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 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 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 Threshers high-pressure air flasks, which froze and plugged its own flowpath while passing through the valves. This was later simulated in dock-side tests on the Thresher's sister ship, USS Tinosa (SSN-606). 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 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 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, Lt. 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 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. 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.
There was much (covert) criticism of Rickover's training after Thresher went down, the argument being his "nukes" were so well conditioned to protect the nuclear plant 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 and 2,000 feet (400 and 600m). All on board were killed nearly instantly (1 or 2 seconds at most).
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. During the formal inquiry, it was discovered 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 Thresher 's engine room layout was awkward, 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 flood control levers, 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 necessarily performed by hand on Thresher. Hand-power valves might not even have been accessible during a flooding casualty: at such depths, the blast of water from even a small leak (a "water spike") can dent metal cabinets, rip insulation from cables, and even cut a man in half. (Water pressure at 1,000 feet (300 m) is about 450 psi (3,100 kPa).)
SUBSAFE would prove itself to be a crucial part of the Navy's safe operation of nuclear submarines, but was disregarded just a few years later in a rush to get another nuclear sub, Scorpion ready for service as part of yet another program meant to increase nuclear submarine availability. The subsequent loss of Scorpion reaffirmed the need for SUBSAFE and 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.
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).