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Wednesday: 1300, April 10, 1963. I was on the lower base at New London sitting with Sneed Schmidt in his COMSUBFLOT 2 office, along with John Elmer Dacey, COMDESDEVGRU, and my Chief of Staff, Jim Bellah. The subject being discussed was: increased tactical R&D exchange between SUBDEVGROUP 2, my command in New London, and Dacey’s command in Newport, RI.

Sneed’s flotilla radioman broke in — anxiety all over his face — and said to Sneed, ttCommodore, SKYLARK reports something gone wrong with THRESHER.” Sneed had OPCON for all subs in the New London and Portsmouth Shipyard OP areas. THRESHER belonged to my SUBDEVGROUP 2. I cannot remember the rest of the day’s events except for massive confusion and concern. Everyone was on the phone at once between Norfolk, New London, Portsmouth, Washington and everywhere else.

At that moment, Schmidt, Andrews and Dacey did not know that some 180 minutes earlier, THRESHER, on a deep dive 220 miles east or Cape Cod, had lost depth control — probably due to major flooding from ruptured internal sea water piping — and passed through crush depth. She then imploded and broke up severely, making a 3-5 knot falling-leaf descent to the ocean floor nearly a mile below. All 129 crew and technical ship riders on board were lost.

At 1300, THRESHER lay on the floor or the Atlantic continental shelf in 8200 feet of water, broken into three major and many, many smaller parts, in a debris field perhaps 2000 feet long and 400 feet wide. (See Figure 1). All of this took place in perhaps a twenty minute period from 10:00 a.m. to 10:20 a.m. on a middle -of-the-week work-day.

Much was written in the sixties about the THRESHER accident, the deep ocean searches conducted in the loss-area in the summers of 1963 and again in 1964, the Court of Inquiry held at the Portsmouth Naval Base in 1963, and later the wide-reaching, costly but necessary Sub-Safe program which was initiated by THRESHER’s loss.

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Many of the old timers know the facts of all this because they were there. But, I’ll review some of the details, from my personal view, for those who have forgotten or who simply never had a chance to review them. And, there is something new here that most submariners, even the old ones. know little about — that is, the photo mosaic made in 1964 of the THRESHER hull debris field. It shows the final product of that very sad day.


In the fall of ’62 and spring of ’63, THRESHER oompleted a Post Shake-down Availability (PSA) at the Portsmouth Naval Ship Yard. As first of a class, THRESHER had been subjected to a full set of extended sea trials in the ’61-’62 period — inoluding a severe, close-aboard depth charging off Key West, Florida.

During the PSA, all internal piping found to be weeping or leaking as a result of the sea trials was fixed. However, a non-destructive test of all internal and external joints was not done because of cost and time. On April 9, 1963, after nine months in the yard at Portsmouth, THRESHER went to sea with USS SKYLARK to execute a series of PSA tests off the Gulf of Maine.

In keeping with the practice of the day, THRESHER made her way into extra deep water (beyond the 1000 fathom curve) for the usual set of deep dives. On the morning of April 10, 1963, a first dive to test depth was scheduled. The rendezvous and underwater telephone contact with USS SKYLARK were made, and the dive commenced. Sometime around 10:00 a.m. THRESHER reported via UQC “undergoing difficulty – everything under control.” Shortly thereafter ballast tank blowing noises and then break-up noises were heard on SKYLARK’s bridge where the UQC was manned. No tapes were made.

What happened?   The evidence is circumstantial. The only real factual information assembled proved to be a review of shipyard test data and the ocean floor   photographs taken during the search.

My view, based on my own involvement with the search for THRESHER, on a review of findings of the Court of Inquiry, and on discussions with the NSRDC structure people is as follows:

  • During the deep dive maybe at 500 to 700 feet — a silbraze joint in one of the many, many sea pressure systems carried away catastrophically.
  • In many ways, the THRESHER engineering plant (outside the reactor) was built like that of a surface ship. Many, many yards of internal sea water piping, servicing a large number of distributed heat exchangers were similar. In late 1962, Dean Axene, commissioning CO of THRESHER had pointed out that the lead paragraph in his “first-of-class” year-one report to the CNO were approximately, “the literally miles of internal sea water piping in the THRESHER are its greatest single design deficiency. In effect, the ocean does not stop at the pressure hull of THRESHER, but is all over its insides.” The joints in THRESHER piping were not welded but rather were coupled by a form of expanded-on joint with a silbraze type of solder as the main strength bond. The silbraze joints had great strength but tended to pull apart under great tensile stress. (It should be noted that the Sub-Safe program replaced much of the THRESHER-design internal sea water piping, hence now only a very few internal systems are under constant sea pressure.)
  • The stream of sea water pouring into the engineering spaces sprayed salt water all over the place in a horrendously chaotic way. The noise, the inundating sea water, sparks, and electrical equipment shorting out — all over the place — compounded the confusion.
  • The reactor was scrammed and main propulsion was shifted to battery power.
  • The operating procedure of the day was to SCRAM the reactor whenever internal flooding or fire occurred. Simultaneously the main steam stop valves between the steam generator and the balance of the main propulsion plant were closed — eliminating the main source of propulsion power. Drawing down steam pressure in the steam generator was considered intolerable because of the potential thermal stress on the reactors. It was subsequently estimated, however, that SCRA~~ING the reactor but continuing to draw down the steam pressure in the steam generator would have given THRESHER a speed of 10 knots or so for several minutes. (Importantly, a new operating procedure in which the main steam stops would remain open was instituted within a week after THRESHER’s loss.)
  • “Blow all ballast!” The emergency blow valves unpredictably froze up. Lights went out all over the submarine. There was near panic in the control room. Battle lanterns were turned on. The THRESHER was taking a large up-angle, yet her depth gauges showed an increasing depth. More speed available? No! Reactor is scrammed. The Commanding Officer, at the UQC felt he shouldn’t panic the people up on the surface. {Wes Harvey, THRESHER’s skipper had been a starting back for Navy. He had done the Nuke course. He had served in NAUTILUS’s wardroom. ) He kept thinking “We’ll pull it out.” But deeper and deeper the THRESHER sank. Then the after end crushed.

(Post accident tests in May-June, 1963, by the Portsmouth Shipyard demonstrated that the THRESHER class’ high pressure blow valves could freeze up when used in an emergency situation. The design was unsat.)

  • The engineering spaces centered at about the main propulsion turbines imploded. A highpressure shock-wave moved forward, knocking bulkheads down. The air compressed to maybe eighty atmospheres — moved everything big and small before it — finally knocking the front end of the boat off. The boat then split into the parts shown in the debris picture. All life was quickly snuffed out.
  • This scenario was based on tests conducted by the structures people at NSRDC in late 1963. The basic assumption was that THRESHER was flooding art, losing depth rapidly, but with a large up angle.
  • Hanging loosely together, the major parts made a falling-leaf path to the ocean floor a mile or so below.
  • Enroute to the bottom, turbulent flow over the broken parts gradually pulled them apart, but not all that much. Light debris spilled out and drifted out of the vertical, but the center of mass still moved at three to five knots downward in a straight line.
  • Everything settled to the ocean floor about 15 to 20 minutes after the catastrophic passage through crush depth.

Construction of the Photo Mosaic of the Debris Field

Most of THRESHER debris was photographed by USNS MIZAR operated by the Naval Research Laboratory. The search-study tool was a camera/magnetometer cocbination, towed from an “erector set” type structure about 10 feet x 2 1/2 feet x 2 1/2 feet.

The towed “fish” was lowered from a large center-well designed into MIZAR for deep oceanfloor surveillance work. Normally, 12,000 feet of tow cable was used, though the water depth of the debris field was only 8200 feet. The towed “fish” wandered almost directly under MIZAR most of the time. Successful search/photo tactics were: (a) at speed 1 to 2 knots MIZAR moved the towed unit through the area of high probability — the towed fish 8200 feet below MIZAR and maybe 15 feet above the ocean floor — with camera illumination OFF, and with magnetometer energized; (b) upon receipt of a strong magnetometer signal — up the cable to MIZAR’s control center — MIZAR would be turned into a tight circle, camera light energized, and everyone hoped!! (c) at the end of an hour of camera action, the tow cable would be hauled in -a 60 to 90-minute task — and the camera film pack taken to the dark room for development, with pictures, if lucky.

The good photographs were assembled into a montage or mosaic to produce an artist’s sketch.

The individual photographs when developed covered perhaps 15 feet by 15 feet of ocean floor, and no more. Many photographs overlapped sections of each other. Also, individual photographs would have different orders of magnification based on the distance of the camera from the object. Additionally, TRIESTE obtained a few photographs (maybe 5J) which also became part of the final photo mosaic.


The photo mosaic carefully developed represents the excellent craft \olork of NISC (Dick Silby) in Suitland, Maryland, where location, and photographs were assembled to scale, on a large floor of one of the NISC buildings. It shows the tail section is in the southern-most portion of the debris field. A section of the main pressure hull — identified as frames 78 to 67 — is over at the easternmost side of the field. The nose section and a portion of the superstructure and hull surrounding the control room is at the northern end of the field. Nearby are a stern plane with added PUFFS hydrophones, along with an air flask, a torpedo shutter door and finally a section of the hull holding the forward escape trunk. There was light, scattered debris all over the area, but their photographs were not included in the mosaic. They required too much detail with too little accurate navigational data. Examples would include: storage battery plates, air flasks, a compartment ladder, twisted metal pieces, a RADCON booty marked “SSN”, a torpedo handling davit, a sonar internal strut, twisted cabling and superstructure plating.

A guess is that the main pressure hull hit first with the reactor-end penetrating deeply into the muddy bottom. Heavily plowed terrain adjacent to this section indicates the impact of a massive body.

The stern section is clearly imploded.It could be approximately frame 78 on aft. This imploded tail section supports the scenario of flooding aft and loss of depth control with large up-angle.

The nose and hull sections are close together and represent the third largest section of debris.

The many other small, yet identifiable submarine parts (anchor, stern plane, sail, torpedo tube shutter) plus much lighter debris not shown, are testimony to the enormous release of energy which must have taken place when THRESHER went through crush depth. One calculation suggests an energy release comparable to the explosion of a ton of TNT inside the boat.

In summary: THRESHER debris field is at latitude 41 44.5 N, longitude 64 56.4 W in 8250 feet of water (See Figure 1.)

The ship broke into three large pieces. four smaller pieces. and a snowfield of light debris which was much too detailed to present in the photomosiac.

No unusual radioactivity was ever observed in the debris field. The reactor compartment was never sighted and is probably buried as an extension of the part of the main pressure hull. TRIESTE (with pilot. Brad Mooney) actually sat on this section for o~er an hour on one of her dives.

THRESHER’s loss was undoubtedly due to design deficiencies — silbraze joints. excessive internal seawater piping, frozen blow valves and an over cautionary concern for reactor thermal stress.

Risk is part of technical progress. THRESHER paid the price for improved operating safety in today’s submarine force.

Frank Andrews

[Editors note: Frank Andrews was Commander of the THRESHER search operation in the summer of 1963 and again in 1964. This article is based on his memories from 20-odd years ago.]

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