Contact Us   |    Join   |    Donate


Captain Martin was a pilot of the Bathyscaph TRIESTE during the search for THRESHER and holds Deep Submergence Operator Certificate #4. He was in the submersible AL VIN when they found the missing H-Bomb in the Mediterranean Sea. After leaving active duty, he settled down to civilian life and initially worked for the Lockheed Aircraft Corporation during the development of the Deep Submergence Rescue Vehicle. The crew of the Bathyscaph TRIESTE was awarded the Navy Unit Commendation for their efforts in the THRESHER search. Don Keach, Captain USN(Ret.), the officer-in-charge, died in 1999.

Part II

Part I related the history of THRESHER and the search for the sunken submarine. Part II provides excerpts from the Court of Inquiry Report and the transition to the SUBSAFE and Submarine Rescue Program of today.


Picture a submarine program that involved five new designs, eleven navy yards constructing and repairing submarines, and one yard with five submarines in work. Submarines had new missions: to launch ballistic and cruise missiles. They also had new requirements for operating depth and quietness, new technologies, nuclear power, and new materials, HY-80 steel. The expanding industrial base was developing new manufacturing techniques, tools and standards, and training personnel. The nuclear submarine pipeline was qualifying crew and officers for these submarines. The Cold War Soviets were increasing the numbers of nuclear and diesel submarines, surface ships and aircraft. Such was the dynamic world of the early nuclear submarine era which produced THRESHER.

Fortunately there was a Congress who understood the necessity of a strong defense, as well as the costs of that defense. Congress was confident of its Navy and its role in peaceful uses of atomic energy. The population was proud of their Navy. They also knew the terrors of atom bombs. It was a huge shock, then, when one of our own atom powered submarines sank in our front yard, off Cape Cod. This was near major east coast population centers. People felt threatened by the loss of the submarine and men, and the word atom powered used by the media.

The extent of the shock galvanized the Navy into immediate actions: (1) they reassured the public that there was no substantive threat from nuclear radiation from the submarine’s reactor, (2) they constrained the operating submarines from a similar accident scenario, and (3) they took steps to find out what happened, and formulated an action plan to prevent a re occurrence.

The Navy provided news organizations with information about the safety of the reactor in 8,400 feet of sea water. Within days the Navy had water sample and core samples taken from the vicinity of the submarine. These showed no radiation above normal back-ground levels. Soviet ships were on scene almost immediately and generated propaganda about radioactive fallout. The Navy had samples taken throughout the summer from both surface ships and TRIESTE, and all samples were within normal levels. The Navy sent pilots in the Bathyscaph directly to the site implying that the radiation hazards were minimal. The Navy continued monitoring radiation levels in 1965, 1977, 1983, 1985, and 1993 with similar benign results.

The Navy took immediate action to restrict the operating depth of all submarines until more was learned about the causes of the loss of THRESHER on 10 April 1963. That night the Commander-in-Chief, US Atlantic Fleet, ordered a Court of enquiry to look into the causes of the loss. In the following days, Congress scheduled hearings before the Joint Committee on Atomic Energy for late June to receive the results of the Court’s Report. The Navy also established the THRESHER Design Review Board, the Submarine Safety Program and formed the Deep Submergence System Review Group. The results of these activities are summarized here along with a brief look at where we are today.

Court of Inguirv Findings of Fact and Opinion

Two unclassified summaries of the Court of Inquiry report were released in June 1963. The first, “THRESHER Court of Inquiry Reports,” was issued 20 June 1963. The three pages briefly told the findings of fact and opinion describing the final two days and minutes of THRESHER’s operations. The opening paragraphs of the three page summary contain the Court of Inquiry’s opinion as to the cause of the loss:

“A flooding casualty in the engine room is believed to be the ‘most probable’ cause of the sinking of the nuclear submarine USS THRESHER, lost 10 April 1963, 220 miles east of Cape Cod with 129 persons aboard.

“The Navy believes it is most likely that a piping system failure had occurred in one of THRESHER’s salt water systems, probably in the engine room. The enormous pressure of seawater surrounding the submarine subjected her interior to a violent spray of water and progressive flooding. In all probability, water affected electrical circuits and caused loss of power. THRESHER slowed and began to sink.

“Within moments she had exceeded her collapse depth and totally flooded.

“She came to rest on the ocean floor, 8,400 feet beneath the surface.”

VADM Bernard Austin, USN(Ret.), was named president of the Court of Inquiry. The court heard from many witnesses and had certain tests conducted before closing on 5 June 1963• The complete classified text, The Report of the Court of Inquiry Findings of Fact, Opinion and Recommendation, listed 166 findings of fact, 54 opinions, and 20 recommendations. The Court of Inquiry’s findings of fact reconstructed THRESHER’s history from building through her final moments. The Court’ s opinions were conclusions drawn from the facts and the special tests and analyses conducted at the Court’s request. The Court’ s recommendations were of three kinds: specific to the THRESHER class, general to all submarines (particularly the deep diving hulls), plus direction to the Bureau of Ships.

Excerpts from the Court’s report follow, between which are comments by the author containing information gleaned from the findings of fact and the Hearings of the Joint Committee on Atomic Energy. The Court’s Findings are in quotation marks. Comments are in plain text.

“Finding of Fact 47. That the increasing operating depths of submarines has compressed the time available in which to take effective damage control action with respect to flooding. The shortness of time available to control flooding is not well recognized.”

Comment: The Court had analyses made of what it would take to sink THRESHER in the six minutes from the reactor shutdown time to the time it passed through crush depth, as recorded by SOSUS.

“Opinion I. That the loss of the USS THRESHER was in all probability due to:

a . An initial flooding casualty from an orifice between 2″ and 5″ in size in the engine room, which continued compounded by
b. Loss of reactor power due to an electrically induced automatic shutdown,
c. Inadequate operating procedures with respect to minimizing the effects of a flooding casualty and the loss of reactor power, and
d. A deficient air system, susceptible to freeze-up, with low capacity and low blow rate.”

“Opinion 45. Had the main turbines remained on propulsion much longer that 0912.SR with the main coolant pumps (classified … ), THRESHER could have surfaced with a flooding casualty due to any pipe rupture in the ship except (classified … )”

Comment: (a) There was a well publicized history of sil-braze joint failure in the 1959-1963 time frame in both nuclear and diesel hulls going to deeper depths. Sil-braze was the best technology available when THRESHER was built. There were an estimated 3,000 sil-braze joints in an S-5-W plant and another 5,000 in other critical systems.

(b) The Court test released a stream of water at test depth pressure to one atmosphere against a piece of electronic equipment. The result was a stream of tremendous force, spray, fog and noise. The conclusion was that the switchboard shorted and the reactor went into shutdown mode.

(c) The operating procedures for emergencies such as flooding were revised within weeks of the THRESHER loss lo allow some valves to remain open to use the energy already in the plant for propulsion.

(d) The Court required a test of the high pressure air system on a sister ship, TINOSA, while on the surface. The strainers in the reducing valves froze up in 30 seconds, stopping air flow.

“Opinion 2. That there is a danger that, in melding together fact and conjecture, conjecture may be stretched too far and become accepted as fact, thus narrowing the field of search for possible causes of the casualty.”

Comment: This was an attempt to stop a rush to judgment that there was one particular cause for the sinking when there were “in all probability” several, and some may never be known.

“Opinion 5. That a flooding casualty to THRESHER could have resulted from:
a. A faulty sil-braze joint.
b. Undiscovered shock damage.
c. A flexible hose failure.
d. A casting or piping failure.
e. A minor hull failure.
f. Unknowns, including component failure.”

Comment: (a) Sil-braze joints were banished from submarines and replaced over time by all welded joints, manufactured in clean rooms, tested by radiography, and certified by Quality Assurance, a new dimension to the manufacturing process. V ADM Rickover required welded joints in the reactor compartment in THRESHER.
(b) Damage from the shock tests was continuously uncovered and repaired during subsequent operations and the Post Shakedown Availability .
(c) Flexible hose failures were common until after December 1963, when new design hose and couplings, and installation procedures were issued.
(d) New procedures for radio graphing castings led to a large number of rejections and eventually more reliable products.
(e) Minor cracks were common in welded sections of HY-80 and considered fixable by BUSHIPS. V ADM Rickover preferred a more shallow test depth which allowed the use of High Tensile Strength steel.

The Court’s Opinions conclude with numbers 54 and 55, and a poignant final sentence:

“Opinion 54: That the lessons learned from the inquiry into the loss of THRESHER are of such moment as to require wide dissemination within the Navy.

“Opinion 55: That the findings and opinions of this court point out numerous practices, conditions, and standards which were short of those required to insure the thorough overhaul and safe operation of the USS THRESHER … Vigorous steps should be taken to correct them.

“These shortcomings have developed incident to the rapid changes in materials, workmanship and operating conditions of submarines during the last decade and to the accelerated pace of the submarine program. They can be blamed on no individual or individuals, and many would not have come to notice had THRESHER not been lost.”

Court of Inquiry Recommendations

The first recommendation was to protect the at-sea submarines:

“1. That the interim depth restrictions now imposed upon all submarines should remain effective until careful consideration, for each individual submarine, is given to the probable factors contributing to the loss of THRESHER, as listed in Opinion .”

Most of the other recommendations can be summarized as, the Navy should conduct:

” … careful review of the design, construction, and inspection of vital submarine systems, such as sea water and air systems, and a review of operating procedures to improve damage control capability under casualty conditions such as flooding.”

The final recommendation was that consideration be given to establishing an organization responsible for the analysis of events and developments related to submarine safety and promulgating information to the fleet. That recommendation was quickly acted on and became the Submarine Safety Center which is now the Submarine Safety Division of the Navy Safety Center in Norfolk, Virginia.

Navy Judge Advocate General Report

The second unclassified report, “Summary of Events Concerning Loss at Sea of USS THRESHER” was released by the Navy Judge Advocate General, 25 June 1963. This contains the Court’s Findings of Fact, Opinion and Recommendations regarding THRESHER’s construction, post commissioning operations, and post shakedown availability.

Hearings Before the Joint Committee on Atomic Energy

The Joint Committee on Atomic Energy conducted hearings in late June and July 1963 to review the Court’s findings and records and a year later, July 1964, to learn what progress the Navy had made. A staff representative was present from the Senate Armed Services Preparedness Subcommittee. The fact that the Atomic Energy Committee took precedence over the Armed Services Committee indicates that concern about radiation from the nuclear submarine was greater than the concern of being attacked by the Soviets. The hearings were held in executive session so that classified information could be presented. The classified report was reviewed and an unclassified transcript was prepared.

Secretary of the Navy Korth opened his remarks in the hearing by noting that the Bathyscaph TRIESTE was going to surface shortly and he had not yet heard of the dive’s results. He had some expectation that TRIESTE would find something of value to the Navy and to the Congress.

Secretary Korth introduced the admirals accompanying him. Korth began with V ADM Rickover, who had issued a new instruction on operating procedures for nuclear reactors, V ADM Austin had completed the Court of Inquiry into the loss of THRESHER, RADM Stephan, head of the Deep Submergence Systems Review Group, was investigating search and recovery in the deep ocean, RADM Maurer, OPNA V head of submarine warfare, was looking into submarine operating practices, RADM Brockett, head of the Bureau of Ships, had set up a Submarine Safety Task Group, and RADM McKee was reviewing the design of THRESHER.

The hearings contain a classic example of the way Congress used its powers of oversight to investigate the serious accident of a nuclear powered submarine with major loss of life. There were many issues with the way THRESHER was designed, constructed and operated and the Joint Committee went into all of them, in detail. A pertinent comment made by RADM Brockett was that in submarine design, we moved too fast and too far in offensive and defensive capabilities, and submarine safety did not keep pace.

THRESHER Design Appraisal Board

The THRESHER Design Appraisal Board, headed by RADM McKee, submitted their report on 15 July 1963. The report recommended improvements in design, fabrication and testing for greater submarine safety. Those recommendations were incorporated into the submarine safety program, which became SUBSAFE.


The Submarine Safety Task Group was established by the Bureau of Ships to carry out the recommendations of the Court of Inquiry and the THRESHER Design Appraisal Board. The original group considered sixteen broad categories including sea water systems, fabrication methods, machinery components, mandatory use of class plans, high pressure air systems, submarine readiness for builders and sea trials and certification, protection of electrical systems, pressure hull penetrators, improved damage control information in ship’s information book, diving trainer improvements, and submarine shock test procedures. The immediate actions were revising operating and casualty control procedures, implementing maintenance and material control requirements and installing emergency ballast blow recovery systems.

Today SUBSAFE is carried out by the NA VSEA Submarine Safety and Quality Assurance Division. Their mission is “to promote maximum reasonable assurance that seawater is kept out of the submarine and that the submarine and crew can recover if there is a seawater casualty.” The technical and administrative requirements for SUBSAFE are contained in the Submarine Safety Requirements Manual.

Deep Submergence Systems Project

The Deep Submergence Systems Review Group was formed in April 1963 to review current plans for location, identification, rescue, and recovery of large objects from the deep ocean floor. The Chairman was RADM Stephan, former Oceanographer of the Navy. They examined many scenarios. Three that generated much concern were: (I) a submarine sunk at a depth deeper than the McCann chamber capability but less than the collapse depth of the submarine,
(2) recovery of small objects (missile nose cones) from the deep ocean,
(3) a SSBN with its nuclear missiles sunk in international waters. The group presented innovative plans in their final report one year later. The CNO gave management of the report’s recommendations to the Director of Special Projects, who later established the Deep Submergence Systems Project to implement the recommendations.

The project was initially responsible for development of a Deep Submergence Rescue Vehicle (DSRV). a Deep Submergence Search Vehicle (DSSV), and a Large Object Recovery System of something as large as a POLARIS submarine. Later SEALAB, the underwater habitat, and NR-1 were added. The project’s most urgent task was to develop the DSRV that could rescue submariners to a nominal depth of 2,000 feet. The DSRV-1 and DSRV-2 were launched in 1970 and 1971 respectively. Eight mother submarines were modified to transport the DSRV submerged to the downed subma-rine, avoiding wave and weather. DSRV-1 and DSRV-2 performed successfully in exercises and, fortunately, never had to be deployed in a submarine emergency. The DSRV’s have conducted exercises with US submarines and those of foreign navies. The DSRV-1 was taken out of service in 2000, and the DSRV-2 is in service until about 2005, depending on the phase-in of the follow-on escape and rescue systems.

The DSSV project, originally a manned 20,000 foot submersible, was terminated in favor of a classified project. Man-in-the-Sea, weeks Jong experiments in saturated diving, developed applications usable in submarine rescue. The Large Object Recovery project was overtaken by the CIA Project Jennifer. The Glomar Explorer’s audacious raising of the Soviet Golfll missile submarine, K-129, are well publicized.

Deep submergence search, diving, and salvage systems have performed important missions for the US. Three examples we know about are:

  • found and retrieved the Air Force’s H-Bomb in 2,800 feet of water in the Mediterranean, 1966
  • found and inspected SCORPION in I 0,000 feet in the Atlantic, 1968-69
  • found and retrieved parts of the Space Shuttle CHALLENGER in 1986.

Submarine Survival, Escape and Rescue

Key issues in submarine escape and rescue are: where is the submarine, how soon can a rescue system arrive on site, what will the condition of the crew be by the time it arrives, and what will be the sea and weather conditions. A submarine rescue system is costly to design, build, and operate, and seldom, if ever, needed for a genuine emergency. The Law of Large Numbers tells us that seldom does not preclude it from happening today. The system seems expensive until you look at the opportunity cost of not having it. What would it cost if a US submarine sank in rescuable waters and the Navy did not have the capability to perform the mission? Ask the Russians.

Submarine missions have expanded since the DSRV concept of operation was conceived in the 1960s. US submarines now operate in the littoral areas of the ocean as well as the classic deep oceans. The DSR V concept of operations included a fly-away rescue system, predeployed ASRs with Submarine Rescue Chambers on board, and mother submarine SSNs. Now there is one DSRV, no ASRs, and the mother submarines are diminishing in number. The primary escape system now being phased into service is the Submarine Escape and Immersion Suit. This will enable submariners to escape from a nominal 600 foot depth.

In development is the Submarine Rescue Diving and Recompression System with a 2,000 foot depth capability. This will be air deployable, then loaded onto a vessel of opportunity for transportation to the site of the downed submarine. The system has several elements: the Pressurized Rescue Module, the Submarine Decompression System and control equipment, and generator vans. The Rescue Module is tethered and surface controlled to locate the submarine and then maneuvered onto the hatch. The attendant can monitor the environment in the submarine, and when safe, open the submarine’s hatch. The module can take on board up to sixteen evacuees. The module is then hoisted onboard the vessel of opportunity and mated with the decompression chamber element of the system. In addition to development, the system must undergo a certification process for safety and habitability up to five atmo-spheres of pressure.


The loss of THRESHER and its crew created the demand for new and improved ways of designing, constructing and operating submarines. Today the Submarine Safety Division of the Navy Safety Center and the SUBSAFE program of NA VSEA have responsibility for continuing these efforts. The loss of the men of THRESHER brought about the DSRVs and the follow-on developmental escape and rescue, diving and salvage systems. We owe a lot to the men of THRESHER.

Naval Submarine League

© 2022 Naval Submarine League