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USS Thresher (SSN-593) 3 August 1961 - 10 April 1963

April 1, 2013 | By E. W. Grenfell, Vice Admiral, USN & published in the March, 1964 issue of Proceedings magazine
Photo By: NHHC
VIRIN: 180411-N-ZW259-8838

On 10 April 1963, the U.S. Navy suffered the loss of the nuclear submarine Thresher, the nation's third peacetime submarine loss since World War II, and by far the United States' greatest single submarine disaster in terms of loss of life. The public, both in the United States and abroad, reacted with compassion for the families of these men who gave their lives in the cause of freedom and pioneering. Seamen the world over have expressed reverent respect for these gallant men who paid part of the eternal tribute demanded by the sea from those who dare to venture on, or beneath, the trackless waters.

From our very beginnings, our country, like other leading maritime nations, has relied upon the sea to carry arms as well as commerce. In the process of maintaining our maritime skills in the naval profession, the United States has become a foremost submarine power; this happened almost by default. After Pearl Harbor, our submarine forces were elevated to an unexpectedly important place in our Fleet because of the initial destruction wrought on U.S. surface warships. In fact, only the submarine forces retained the full capability to carry the war back to the Japanese immediately. The highly successful submarine campaign during World War II was, of course, based on the efforts of brave and intelligent men. But it was also based on the peacetime work of other men equally brave and competent, for, in 1941, the United States possessed the finest submarines in the world and the men who knew how to sail them. Many of our present diesel submarines are modernized first generation descendants of these World War II Fleet Boats.

The U.S. Navy, during the years from 1920 to 1939, constructed a series of classes of submarines, each of which was operated by our Fleet until its characteristics were known and evaluated. The knowledge thus gained was used to improve succeeding classes. In the process of building up this superior submarine force which broke the back of the Japanese merchant marine and contributed so much to the defeat of her fleet, approximately 150 men gave their lives in peacetime submarine accidents. The S-51 was rammed and sunk by the steamer City of Rome in September 1925 with the loss of 33 lives; in December 1927, the S-4 was rammed and sunk by the Coast Guard destroyer Pauling with the loss of 40 lives; the Squalus flooded and sank in May 1939 with the loss of 26 men; and the 0-9 was crushed while exceeding test depth in June 1941, taking 33 lives. Though their former shipmates mourned these losses, U. S. submariners returned to sea determined to build better submarines and to operate them more effectively and safely. It was the dedicated efforts of these men that gave us the ships and know-how we needed so desperately on 8 December 1941.

The recent tragic loss of the Thresher is a sad but gallant extension of the tradition of duty, professional competence, and self-sacrifice which has always been the hallmark of the submarine forces of our Navy. 
Just as surely as in any combat casualty, the ship's company, and the military and civilian observers and technicians embarked in the Thresher on her last dive, gave their lives to insure the survival of our way of life. These men were lost testing a class of submarine which fits into the spectrum of submarines available to the world's navies today exactly as did the marvelous Fleet type of the last generation. The outstanding safety record of our submarines in recent years, along with our own demonstrated confidence, had led those who did not fully understand submarine operations to forget that such operations are still hazardous duty and involve a certain amount of calculated risk. When sailormen of the United States no longer choose to face the dangers of the seas, our nation will cease to exist.

Just what kind of a ship was the Thresher?
She was the result of the quantum technological advances coming from the technological revolution of the past decade. The Thresher was without question the most advanced operational attack submarine in the world. She was the fastest, deepest-diving, quietest, and best-armed submarine ever delivered as an operating warship to any fleet. She had been with the Fleet from her commissioning on 3 August 1961 until she entered Portsmouth Naval Shipyard on 16 July 1962 for post-shakedown availability. Her performance at sea fully confirmed the anticipated quantum advance in attack submarine capabilities which the designers had promised. The Navy had depended upon this performance to the extent that it had asked for and received authority to build 14 of these ships, as well as an additional 11 SSNs with very much the same characteristics. This was the first time since World War II that we had considered our design sufficiently advanced to embark upon construction of a large class of general-purpose attack submarines.

The Thresher showed us during her year in the Fleet that she could surpass the best we had hoped for when we placed her in the hands of our submarine sailors. She could and did shoot the most advanced torpedoes. She was also fitted out to launch the new anti-submarine missile SUBROC which is now under development. She could make high speed with very little noise. Her sonar, both active and passive, was extremely impressive, and this vastly improved detection capability was further enhanced by her ability to operate at great depths over a much wider range than heretofore. She was shock tested and withstood this depth-charging in a manner far superior to that of any submarine the U.S. Navy had previously tested. This was the most severe shock test we have ever conducted on a submarine in service, and the Thresher suffered only minor equipment failures - in other words, she was not only a fancy performer, she had more built-in damage protection than we had ever before achieved. She had been at or near her test depth at least 40 times. In all, she was a marvelous submarine. She had been worked out by a blue ribbon crew, and she had established our confidence in the soundness of her basic design.

This confidence was reaffirmed by the Court of Inquiry after her loss.
As do all Navy ships after their shakedown, the Thresher returned to a naval shipyard for necessary repairs, corrections, and alterations after having been operated long enough to check the systems out thoroughly. She had performed beautifully, and her anticipated repairs were in no way cause for particular concern. Conjectures in the press concerning damage to a ballast tank by a tug and her failure to complete her initial deep dive during builder's trials because of faulty instrumentation cannot be tied to her later loss, by either scientific or rational means. She went into the yard a fine ship sailed by a ship's company which represented the best talent in the Navy, and she put to sea later under the same circumstances.

The Thresher arrived in the Portsmouth Naval Shipyard at Kittery, Maine, on 16 July 1962 and was expected to depart on about 18 January 1963. Her availability was later extended, primarily to permit additional modifications for silencing machinery. This extension of an availability is not unusual. It is considerably less expensive to accomplish all applicable modifications while interference in the way of such work is already removed, rather than to postpone these modifications until a later availability. This is the same decision many of us have made in having mechanical work done on our automobile. Once the engine is taken apart for some reason, it is frequently the economically sound decision to replace piston rings or bearings or to regrind valves at the same time. So it is with work inside a submarine where access to machinery and equipment under normal conditions is difficult. When the decision to delay is made, however, we are always faced with the possible effect this will have on the crew's morale. These men are seamen who want the best of everything for their ship, but most of all they want to sail her.

The Thresher's crew must certainly have been eager to take their fine ship to sea after having spent so much time getting her ready. As is usual with the first ship of a class, her long stay in the Yard was in large part the result of the Navy's policy, of incorporating all possible advances in equipment and technology expected to be built into later ships of the class. This gives us the ability to evaluate the results of advances in new equipment in an operating ship at the earliest possible date. If we were to wait for a later ship, she would have to go through shakedown in order to achieve the degree of crew proficiency which would then permit her use for evaluation in an operational environment. On 4 April, the Thresher was drydocked to permit final work on hull fittings, and on the 8th, she was undocked and moored to a pier while her crew completed final adjustments and tests with the shipyard personnel in preparation for sea trials. Prior to this time, the crew had " operated" the ship alongside the pier to test all equipment. These tests, the dock trials, include what is known as the "fast cruise," a trial period during which the crew buttons up the ship and goes through virtually all the routine concerned with taking the ship to sea and operating her. This testing is done on an around-the-clock basis and may consist of several days of uninterrupted "steaming." No access or egress is permitted. This is the final extensive testing of all the ship's equipment before going to sea.

Additionally, the ship's company gets its first chance to operate as a team complete with the new men who have joined the ship in the shipyard and those who have been advanced to more demanding duties. Thus, prior to leaving port, the men are integrated and trained, and they become the closely coordinated group which the crew of an operating man-of-war must be.
On 8 April, the Thresher, under the command of Lieutenant Commander John W. Harvey, U.S. Navy, had all of this behind her. At about 0200 on the 9th, her engineers commenced bringing her nuclear plant critical. By 0700, the plant was warmed up and ready to go, and the word was passed on the ship's general announcing system to "station the maneuvering watch." At 0805, after having completed all of the checks of communications, instrumentation and ship control equipment, the Thresher got underway and headed for sea for the first time after nearly nine months of overhaul. Surely the men on board were in a relieved and happy mood to have arrived at this milestone in the process of getting their superb ship back in operation. Undoubtedly, they had at all control stations, and on the crew's bulletin board, copies of the Sea Trial Agenda promulgated by the Thresher Notice 9080 of 2 April. This was an integrated schedule for each test required on sea trials. Satisfactory accomplishment of the events on this agenda would put the ship well on her way to rejoining the Fleet.

The submarine rescue ship USS Skylark (ASR-20) from Submarine Squadron TEN in New London had been ordered to rendezvous with the Thresher at 41-42' North, 62-27' West at 1100. From this position, the two ships proceeded in company to an operating area off Boston where the Thresher was to conduct her initial trim dive and her half-test-depth dive. The initial dive is made deliberately and slowly, and the diving officer pumps, floods, or transfers water ballast based upon the behavior of the ship as she submerges. Once he has made his adjustments, ship control is normal and not difficult. The next event, a deeper dive to less than test depth, is made in salvageable waters - waters in which the submarine can be reached by rescue equipment and possibly salvage equipment in the event of a major casualty with resultant bottoming.

Before putting to sea, every piece of pipe or machinery which must carry sea pressure has been hydrostatically tested to a pressure equal to that to be found at at least one-and-a-half times test depth. The hull of the ship has been tested for leaks, compartment by compartment, using internal air pressure. All welds and hull fittings have been inspected scientifically for strength and integrity. But it is only during the first sea trials that the submarine is tested under external pressure as a complete ship for the first time. During these trials following construction or overhaul, machinery and piping systems must adjust to hull compression, but of course the systems and equipment are designed to accommodate these additional stresses which are difficult indeed to compute.

When making the first test dives after extensive repairs or work, the submarine will descend in stages of 50 to 100 feet with most internal piping secured from sea pressure or with valves throttled and the water-tight doors shut and ready to be dogged. At each stage, sea pressure will be cut into sea-water systems sequentially and the piping and machinery carefully inspected. If any system is found to be defective, the defect or leakage will either be corrected or the system or equipment secured and not subjected to further tests until repairs can be completed. In the case of vital systems or equipment, the finding of defects may result in discontinuance of the trials. Under this procedure the chance of an abrupt failure occurring is minimized.

Submariners learn to live with water under pressure from the beginning of their training, but the threat of serious flooding is never taken lightly. The pressure of the sea increases alta rate of .44 pounds per square inch for each foot of submergence. This means that at 100 feet, the pressure of the sea is 44 psi and at 400 feet, it is 176 psi. City water systems usually deliver water at approximately 15 psi at the faucet.
Large fire hoses deliver water normally at approximately 50 psi. A quarter-inch gauge line at 400-foot depths delivers a stream of water that looks like a stream from a fire hose. The rate of flooding, along with accompanying noise and fog or mist resulting from a one-inch opening at the depths at which the Thresher was capable of operating, is something beyond the imagination of most of us. The Thresher's experienced personnel, however, were well aware of the factors involved in flooding and other casualties at deep depth and were trained to respond rapidly to emergency situations.

The Thresher successfully completed her initial submerged tests on 9 April in salvageable waters and released the Skylark with instructions to rendezvous in the morning for the conduct of the test-depth dive. The Skylark proceeded to the morning rendezvous point and the Thresher continued to follow her Sea Trial Agenda, conducting various tests en route to the deep-dive position. At approximately 0635, the Thresher joined the Skylark at a position about 220 miles east of Cape Cod. The Thresher was still submerged. The two ships exchanged calls by radio and underwater telephone, and the Thresher reported her range and bearing from the Skylark, as well as her course. She then commenced her dive to test depth, using the standard practice of stopping at intervals to check carefully the integrity of sea-water systems. The depth of water at the deep-dive position was approximately 8,400 feet.

At about 0917, communications with the Thresher were lost.
The last transmission was garbled when received by the Skylark. While it is now believed that this garbling could have been caused by the Thresher blowing air into her ballast tanks, the same phenomenon can be observed when the submarine is passing through a thermal layer, or when there is turbulence around the receiving ship. The interruption of communications by itself was not necessarily cause for alarm. Outside of submarine circles there, has been some question as to why the Thresher was making her dive in such deep water. The answer to this question involves both safety and geography.

The modern deep-diving submarine has advanced so fast that our rescue and salvage capability has dropped far behind, and it will probably be some years before we have even a rescue capability at the crush depths of the new submarine hulls. We therefore must do the best we can to insure the submarine's ability to save herself. At deep depth, the most effective first step to combat continuous flooding is to reduce quickly the sea pressure on the leak and also the sea pressure opposing the ejection of water from ballast tanks. This is done, of course, by changing to shallower depths as rapidly as possible.

This change of depth requires speed, either residual after a loss of power, or powered speed to drive the ship upward where her ballast-tank blow system and her pumps will be more effective. Since one of the greatest needs is for speed, we must be sure that we give the submarine ample opportunity to use it. In other words, we must assure that at test depth - the maximum intended depth in a test dive - here remains sufficient water under the submarine so that she will be free to use speed to return from any depth at which she can survive. If the ship were to run into the bottom at medium or high speed well below test depth, with the hull under severe compression, a collision with the bottom could very likely be disastrous, while the ship might very well survive the excursion otherwise. Therefore, our effort, since we must operate beyond the reach of rescue equipment, is to insure that the submarine operates in a depth of water sufficient to preclude a bottom collision at any depth in which she could otherwise recover and survive.

As is well known to all seafaring men, the geography of this continent features a plateau on the sea bottom, which extends 50 to 300 miles from the East Coast and then drops off abruptly in underwater cliffs more than a mile high. For deep dives with modern submarines, we need depths which are generally greater than those encountered on the Continental Shelf. For these reasons, then, we are required to conduct deep trials in the waters beyond the Continental Shelf. Otherwise, we must make very long transits to dive in the small depressions of the Shelf in water which is shallower, but still beyond our rescue or salvage capabilities. When our rescue capability is developed to match the depths required for deep tests of our new submarines, then surely, we will make our deep test dives in waters where salvage operations could be conducted.

It should be made clear, however, that the development of a deeper rescue capability will provide a greater measure of safety only in certain narrowly defined situations. The very large majority of a nuclear submarine's normal operating time still will be spent in water depths where the possibility of salvage and rescue is non-existent. This is a calculated risk which submariners have always taken, and it is no greater than the risks taken by aviators the world over or by men in countless other professions. But at 0917 on 10 April 1963, there was very little that the submarine rescue ship Skylark could do beyond hoping that the loss of communications was a temporary condition, owing to a temperature gradient, or that, if a serious casualty had occurred, the Thresher would be able to emergency surface so that the Skylark, with her towing, fire fighting, and special damage control talents, could assist.

The submarine rescue ship provides a reservoir of talent able to assist a ship in distress. The deep sea divers and other personnel - machinists, welders, burners, riggers, torpedomen, boatswains, metalsmiths, etc. are masters of a number of trades, and many are so technically capable that they are able to use their skills in the murky depths, guided by touch alone. The last message, though garbled, had indicated that the Thresher was having problems and was trying to blow ballast, either to surface or to rise to a shallower depth while correcting her problems. The Skylark immediately informed the Thresher that the area was clear of shipping so that she would feel free to come all the way to the surface if she desired.

The procedures to this point were quite normal in sea trials. A primary duty of the escort is to keep the area of the dive clear in order that the submarine may broach or surface safely without prior notice and so that the submarine can be informed of surface conditions in the event of an emergency. This time, however, the Thresher was not seen to surface, and as concern mounted, the Skylark's commanding officer commenced sending emergency signals and started a close area search.

As the Skylark failed to regain contact with the Thresher, a message was sent indicating that contact with the Thresher had been lost and that a search was underway.

This message was received by Commander Submarine Flotilla Two, in New London, in the early afternoon. Naval commands up and down the East Coast were ordered to move forces into position to assist in search and rescue. The USS Seawolf (SSN-575) and the USS Sunbird (ASR-15), were diverted from normal operations to the Thresher area. Commander Submarine Force, U.S. Atlantic Fleet was given a list of all ships within 100 miles of the Thresher area from the Atlantic Fleet Movement Report Center. Messages requesting the Thresher to report were placed on the submarine fleet broadcast, which is copied by all submarines at sea. Naval Air Station Quonset Point, Rhode Island, sent a helicopter to New London to transport Captain Frank A. Andrews, U.S. Navy, Commander Submarine Development Group Two - the Thresher's Squadron Commander - to the USS Norfolk (DL-1).

Captain Andrews boarded the Norfolk at sea at approximately 1700 and headed toward the search area. The Thresher still had not been contacted. At 1840, Rear Admiral Lawson P. Ramage, U.S. Navy, Deputy Commander, Submarine Force, U S. Atlantic Fleet embarked in a helicopter at New London for transfer to Newport, Rhode Island, where he embarked in the USS Blandy (DD-943) which was in port, fueling. At 2030, the Blandy sailed for the search area. By the time Admiral Ramage departed Newport in the Blandy, there were 15 ships en route to the Thresher's last position, or making preparations to sail. These ships included destroyers, submarines, seagoing tugs, submarine rescue vessels, frigates, one Navy oceanographic research ship and the civilian research vessel Atlantis II, from the Woods Hole Oceanographic Institute. The fleet oiler USS Waccamaw (AO-109) was preparing to sail from Newport on 11 April to refuel search units on the scene. Aircraft from naval patrol squadrons on the East Coast were assisting in the search. Families of the next of kin of those on board the Thresher were being notified that the ship was overdue.

As the Thresher failed to respond to all signals and the time for sending the normal surfacing report elapsed, the hope that she had broken contact by inadvertently moving beyond visual and communications range from the Skylark faded. At 1700, when the USS Recovery (ARS-43) arrived on the scene, she discovered an oil slick very near the Thresher datum.

At 1830, Commander Submarine Force, Atlantic Fleet notified the wife of the Thresher's Commanding Officer and commenced notifying the other next of kin that the Thresher still had not been heard from and had been officially declared missing.
At this time, the search group being assembled at the area was designated Task Group 89.7 by Commander in Chief, U. S. Atlantic Fleet. Rear Admiral Ramage assumed the duties of Task Group Commander.

By approximately 2100, it became apparent that there were no survivors and that the Thresher had indeed been lost in more than 1,300 fathoms of water. Enough debris had been recovered to indicate a major casualty, and the surface area had been searched sufficiently to insure that there had been no survivors. To wait longer in declaring the ship lost would have been cruel to those who were waiting and praying for her safe return.
Task Group 89.7 now had the tremendous challenge of locating a sunken submarine at great depth so that, if possible, the hull could be examined by underwater photography and other means in an effort to determine what had caused the loss. The rescue force that was fast assembling had a search capability unsurpassed by other than special oceanographic research ships. This search consisted of a careful, visual, Fathometer and sonar examination of the area around Thresher's last-known position.

Destroyers carried debris ashore to various laboratories for analysis and resupplied the search force with equipment and scientific personnel. About 39 hours after the last message from Thresher, Rear Admiral Ramage, embarked in the USS Blandy (DD-943), was in the search area with five additional destroyers, two submarine rescue vessels, one salvage ship, two submarines, the research ship Atlantis II, and patrol aircraft from two Navy patrol squadrons. En route to the area at this time were the SS Rockville (EPCER-851) with a special precision Fathometer, USS Redfin (SS-272), a specially fitted submarine, and the USS Hazelwood (DD-531) carrying special, deep-mooring buoys as well as personnel and instruments from Woods Hole Oceanographic Institute, to be transferred to Atlantis II.
The result of this initial search effort was as follows:
  • The USS Recovery obtained bits of white plastic and samples of oil slick.
  • The USS Skylark recovered several pieces of cork, one piece of yellow plastic, and a small tube of "Bakers Flavor."
  • The USS Blandy sighted several pairs of rubber gloves, and pieces of yellow plastic material-one piece of which was recovered for analysis.
  • The USS Sunbird recovered several pieces of plastic and two rubber gloves.
  • The USS Warrington picked up one rubber glove.
  • The RS Atlantis II obtained water and bottom samples from the vicinity of datum. These were tested for radioactivity. There was none above normal background radiation.
The results of this initial effort confirmed that the search forces were in the vicinity of the Thresher. At 1520 on 12 April, since Thresher had not been located, it was decided to reorient the search to a more-detailed scientific effort with precision equipment and special ships. The warships in the area had exhausted their capabilities without having been able to pinpoint the hulk. Rear Admiral Ramage was ordered to turn over the search force to Captain Andrews in the destroyer Warrington for the longer-term effort. Warships were released, and research ships began to assemble in the search area.

The operations for nearly two months thereafter followed a pattern which was about as follows: the datum area of approximately 100 square miles was divided into sectors which could be surveyed accurately by the ships present. These ships, using precision navigation, surveyed the designated sectors employing all available sensors, i.e., Fathometer, magnetometer, TV camera, etc. The information obtained was relayed to the search group commander and then to Woods Hole Oceanographic Institute where it was analyzed by scientific personnel gathered there by the Chief of Naval Operations' technical advisory group under Captain C. B. Bishop, U.S. Navy.

These scientific and technical personnel represented the best talent in the country in their fields of endeavor, and they had been assembled from both military and civilian laboratories across the country. During the survey phase, research ships were fitted with successively more sophisticated equipment, as the scientific community responded with all-out effort. By June, the area had been thoroughly charted, the datum had been buoyed, ships were navigating with Loran "C" and Decca, and a cartographic and photographic laboratory was in operation on board the USNS Mission Capistrano (AG-162), a specially fitted oceanographic research ship. Photographs of the bottom had been taken showing widely scattered debris which was almost certainly from the Thresher, although the only positively identified object was a high-pressure air flask.

Throughout the long search, the destroyers from Newport, Norfolk, and Charleston provided required transportation to and from the search area, carrying equipment, mail, and personnel. These destroyers also provided the major communications link between the Task Group Commander and Commander Submarine Force, U. S. Atlantic Fleet. On 11 April, the Bathyscaph Trieste had been ordered made ready for the Thresher search operations. This research vehicle, which holds the world's record for deep submergence, was at that time located at the Navy Electronics Laboratory in San Diego. She was quickly prepared for the move and was brought to Boston in the USS Point Defiance (LSD-31). Several factors had to be carefully considered before committing the Trieste to the search. A primary consideration was the Trieste's operational limitations - her slow submergence speed of less than two knots, her endurance on the bottom of approximately four hours, an expected search width of only 100 feet, and the requirement for examination and refurbishment after each series of dives.

It was apparent that the Thresher's location should be fixed as accurately as possible before committing the Trieste to the search, if there was to be reasonable hope of success. As the public is aware, the Trieste was finally committed to the search, but was unable in the initial series of dives to develop much more definite information than our research vessels had already obtained. The Trieste's observations and photographs, however, confirmed that the position of the hull or hull sections was probably very near the heaviest debris area, which was now accurately fixed. The Trieste's return to port signalled a renewal of effort on the part of the oceanographic research vessels. Each type of sensor employed, photographic, magnetic, ionic potential, radiation, TV, and drag lines gave some encouragement. None pinpointed the main wreckage. One of the major problems was that of maneuvering sensors at the far end of a mile and half of wire beneath a ship - very similar to flying a kite to an exact point in space while blindfolded. It took as long as two hours to get a ship's motion stopped sufficiently to get a clear camera picture.

Since the photo width coverage was only 30 feet, it was necessary to navigate accurately to within a 10-yard radius in the open sea in order to return to a desired spot. Such an operation weeds the men from the boys, among the seamen as well as the scientists. During the search, the Navy was assisted by nearly every oceanographic laboratory on the East Coast, as well as by every major Navy scientific facility in the country. Most of the hydrographic ships in the Atlantic were employed at one time or another, and their dedicated crews and the scientific personnel aboard compiled a proud record of performance. The Atlantis II from Woods Hole, an old-timer in this oceanography game, played a key role from the very beginning when she headed for datum upon intercepting a newscast and volunteered to assist. She remained almost continuously at sea in the search area for the first two months. Also participating with distinction were the USNS Gibbs (AGOR-1), the USNS Conrad (AGOR-3), the USNS Gilliss (AGOR-4), the USNS Mission Capistrano (AG-1 62), the USS Prevail (AGS-20), the USS Rockville (EPCER-851), the USS Allegheny (ATA-179), the USS Preserver (ARS-8) and the USS Fort Snelling (LSD-30). The work of these ships under the operational control and command of Captain Andrews, and the work of many of the nation's foremost oceanographic research experts which was co-ordinated by Dr. Arthur Maxwell of the Office of Naval Research, has been publicly recognized as it well should have been.

The search was officially terminated, at least for 1963, on 7 September following the Trieste's second series of dives during which photographs were taken of large, heavy pieces of debris which were positively identified as having been part of the Thresher. Included were clear photographs of part of the bow section showing the submarine's draft marks. It was obvious from this evidence that the Thresher was not intact and that no hope remained of gaining a clue as to what caused the Thresher to sink below her collapse depth. The Trieste's efforts during this and the previous series of dives is certainly in the category of a modern saga of the sea. Lieutenant Commander Don Keach, U.S. Navy, the Trieste's Officer in Charge, the other operators, and the maintenance crew safely operated this fragile research vessel often under the most adverse conditions, to perform a task for which the vessel was not designed.

The award of the Navy Commendation Medal to Lieutenant Commander Keach and the Navy Unit Citation, to the Trieste is but a small measure of the courage and persistence of the recipients of these awards. The public is well aware that a Court of Inquiry was convened as soon as the Thresher was known to have been lost. A distinguished Flag Officer, Vice Admiral Bernard L. Austin, U.S. Navy, President of the Naval War College and a submariner, was named President of the Court. He was assisted by Rear Admiral L. R. Daspit, U.S. Navy, Commandant of the Sixth Naval District and formerly Commander and Deputy Commander Submarine Force, U.S. Atlantic Fleet; Captain W. C. Hushing, U.S. Navy, Superintendent of Shipbuilding at Groton, Connecticut, an Engineering Duty Officer with extensive experience in the design, construction and repair of nuclear submarines; Captain J. B. Osborn, U.S. Navy, Joint Strategic Target Planning Staff, and the first Commanding Officer of the USS George Washington (SSRN-598); and Captain N. C. Nash, U.S. Navy, Commander Service Squadron Eight and now Assistant Chief of Staff of Commander Submarine Force, U.S. Atlantic Fleet. Captain S. Katz, U.S. Navy, was Counsel for the Court.

This Board represented probably the best combination of technical qualifications, operational skills, stability of temperaments, and intellectual objectivities that could have been assembled for this investigation. Their mission was to fix, if possible, the cause for the loss of the Thresher. We now know with almost absolute certainty that this will never be done. However, the Court was able from the evidence available to arrive at a reasonable and convincing rationalization of probable events leading to the loss of the Thresher. It is believed that a piping system failure occurred in one of the Thresher's salt-water systems, probably in the engine room. The casualty must have occurred when the ship was at or near test depth, which subjected the interior to a violent spray of water and progressive flooding. In all probability, water and spray shorted out vital electrical circuits causing a loss of propulsion power. The Thresher presumably blew main ballast, started to rise, then slowed, and began to sink. Shortly thereafter, she undoubtedly exceeded her collapse depth and plunged to the bottom.

The Court heard testimony from 120 witnesses, both military and civilian, during the eight weeks it was in session at the Naval Shipyard, Portsmouth, New Hampshire. It recorded 1,700 pages of testimony and gathered for the record some 255 charts, drawings, letters, photographs, directives, debris, and other exhibits bearing on the sinking. The Court's examination extended into every minute detail of design and construction of this class ship, her post-commissioning operations, and post-shakedown yard availability. After this examination, the Court declared that, in its opinion, "the basic design of the Thresher-class submarine is good, and its implementation has resulted in the development of a high performance submarine." The majority of the Court's recommendations, however, stated the need for careful review of the design, construction, and inspection of vital submarine systems such as seawater systems and air systems, and a review of operating procedures to improve damage control capability under casualty conditions such as flooding.

The Navy took immediate steps to implement these recommendations; one of the most important of which included the development of an inspection technique to assure the integrity of high-pressure piping systems. Silver-braze joints are extensively used in sea-water piping systems in all U.S. Navy submarines. In the past, these joints have been subjected to visual examinations, mallet tests, chemical material re-identification tests and hydrostatic tests. All of these tests were satisfactorily conducted on the Thresher prior to her sea trials; yet, one of these tested joints probably caused her loss. It was immediately apparent that a testing technique must be developed which will absolutely assure the integrity of these critical systems. One technique which shows great promise is based on ultrasonic principles. This method, which has been employed in submarine inspection during the past few years, will now be used more extensively on all submarines. Additional personnel training and ultrasonic equipment familiarization are necessary, so some delays in construction dates and overhaul intervals will be inevitable.

The quality assurance programs at the naval and private shipyards which build or overhaul submarines have been re-emphasized and improved in scope. A system will be established whereby the quality assurance division will be empowered to disqualify workers observed to be violating process controls and normal operating instructions. Audits will be conducted on a regular basis and reported to management. With BuShips overseeing the entire program, substantial improvements are expected. Main-ballast tank-blow systems have been modified, and at sea, submerged tests have been conducted to assure performance of this vital recovery system. Computer studies on the effect of flooding at deep depths have been completed and sent out to most classes of nuclear submarines. Procedures for deep submergence operations for all submarines have been thoroughly reviewed and, where needed, improved operating techniques have been established.

Increased emphasis has been placed on damage control and submarine recoverability training conducted at the U.S. Naval Submarine School and within the Submarine Force. Improved communications and recording equipment has been ordered for our submarine rescue ships. These and many more improvements have been, or will be, implemented during the next few months. Sea-water system-design studies which were started some time ago have been greatly accelerated. These studies will undoubtedly permit a substantial reduction in the amount of sea-water piping required in new construction submarines. It is hoped that eventually our submarines will be built with little or no sea-water piping inside the hull. Additionally, the establishment of a Submarine Safety Center has been proposed. Such a group would represent experts in all technical fields associated with submarines and would be supported by the necessary analytical and statistical equipment.

From the center's studies, we would expect to forecast more of our potential operational and equipment trouble spots earlier in the game. Furthermore, these studies will assist us in improving our rescue capabilities. The complexity of our ships and the size of our present submarine force makes such an organization a must if our Navy is to continue its outstanding record for safe submarine operation. While vitally interested in the submarine of tomorrow, our major concern is the submarine of today. In the years to come, we shall continue to concern ourselves with the design, development, and operation of our submarine weapon systems and with the men who operate them.

Those of us who go to sea in submarines in the future will be indebted to the Thresher for the invaluable knowledge gained from her tragic loss. It is true that the sea has always taken its toll of seamen. But it is also true that no maritime power has survived unless her men have been willing to fight back with successively better ships manned by seamen who have profited by the lessons learned from past mistakes. Our Submarine Force will not fail the heritage we have assumed from the Thresher. We shall continue to inhabit the depths of the sea and to expand our domain there in support of the interests of our proud nation and those of the Free World.