We Remember: USS Thresher (SSN-593)

Updated: April 10, 2013


By RU Special Guest – ET1(SS) Princess

On April 10th, 1963 – exactly 50 years ago – the USS Thresher (SSN-593) silently submerged beneath the ocean depths some 200 miles off the coast of Cape Cod, Massachusetts. Thresher was the new kid on block in terms of submarine design. She had new SONAR, a new reactor, and new weapons systems. She was the U.S. Navy’s newest achievement in the weapons race now referred to as the Cold War and at the time she was the most lethal nuclear attack submarine the world had ever seen.

On the morning of the 10th, the Thresher’s crew was preparing for their day’s assignments; performing sea trials. They began their day by performing a controlled test dive in 100 foot increments, going deeper and deeper, until they would reach her test depth. Her escort ship, the USS Skylark (ASR-20), was floating nearby and communicating via underwater telephone. At or around 0900 hours the Skylark received a message from the Thresher: “…experiencing minor difficulties, have positive up angle, attempting to blow…” This was believed to be a sign that the Thresher was having trouble with the dive and that she was attempting to blow her emergency main ballast tanks, a submarine’s last hope to reach the ocean’s surface. This message was soon followed by the sounds of flowing air through the Skylarks SONAR. Several minutes later, after no further communication, the Skylark’s SONAR heard the sickening sounds of echoing booms; the implosion of bulkheads, tanks, and the Thresher’s hull. With these sounds came the deaths of 129 submariners and civilians.

Thresher and her crew had begun their Eternal Patrol. They had begun a deployment with the crews of previous lost boats the world around; a patrol that will last until the end of time.

The Navy and world were stunned. In one instant, an entire warship with its crew perished. How could this happen? The ego of the world’s biggest and strongest sea power had finally caught up themselves. A full investigation was initiated to determine the root cause of the catastrophe while missions were being prepared to dive to the wreck site. The results of the investigation were jaw-dropping.

It was discovered that there were significant failures in maintenance practices during the ships construction from quality assurance and materials specifications to the physical assembly of the vessel. The shipyard at some points could not even provide the proper documentation to prove the right bolts were used on specific flanges. It was understood and accepted that this was during the Cold War and if the United States did not develop bigger and badder weapons of the sea, that Uncle Ivan would, and could one day come knocking on America’s door. So corners were cut and the heavy envelope of production and pressure folded over the values of safety and quality. Deterrence was the theme based on this methodology and thought process, and it was accepted.

The investigation and diving teams found wreckage strewn across the sea floor. The Thresher had imploded some distance below her crush depth and therefore had thousands of feet to disperse her guts. It was ultimately determined that there was not just one design flaw that failed on the boat, but many. Probably the most significant being that at the time, sea water piping was not welded and flanged but rather brazed. Brazing is essentially a form of soldering. This was far from the safest form of containment when the ocean pressure increases 1 atmosphere (about 14lbs/sq in) every 33 feet of depth.

Sometime after 0900 hours but during her dive, this brazed seawater piping gave way to sea pressure, which at the time probably atomized under the intense pressure. This in turn shorted out vital electrical equipment in the engine room, which led to a sudden reactor shutdown or scram. The ship suddenly lost all power and propulsion. At the time reactor procedures did not designate how to recover the reactor quickly and rather than drive the ship to the surface on what steam was available in the steam generators, procedure directed that the valves to these steam supplies be shut.

The last straw came when the ship attempted to perform her emergency blow. Diffusers in the main ballast tanks were built to spread out air quickly over a wide area. This was thought to help push out as much water as possible, but actually thinned out the cold sea water surrounding the diffusers and thereby froze it. This block of ice sealed itself around the diffusers and prevented any further pressurized air from pushing out the water from the main ballast tanks. It was at this moment, with the engine room flooding, the loss of all electrical power, and the boat slowly sinking stern first into the ocean’s depths that Neptune called his sons home. Thresher’s hull gave way to the immense pressure and perished.

While the U.S. Navy is not always given credit as being in the trenches with the other armed forces, when they do take a hit it is almost always at the cost of many lives. The Navy took a deep hard look inside of itself after the loss of the Thresher and came up with new methods and safety measures to ensure that an accident like this would never happen again. Thus the SUBSAFE Program was born to ensure that no tragedy like this would ever result from failure of equipment or machinery again.

On this day, Submariners the world around will be remembering the Thresher and her crew of 129 men. They will take a few solemn moments to make peace with themselves and the ocean. They will wear their SubVets vests in respect. And all Submariners will remember the men, who have gone before them. They will remember those who are still on Eternal Patrol, and they will relieve the watch, carrying on the duties and responsibilities necessary to bring meaning to the term: “Steel Boats – Iron Men”

You can see more on the Thresher and her crew here.





  1. Mad Medic

    April 10, 2013 at 10:47 am

    Not widely known but just a few days before this test dive, the exploded TNT near the hull to simulate depth charging. after all was said and done the accident investigation also pointed out that they probably shouldn’t have been diving off the coast of cape cod where the water was beyond crush depth.

    The good thing about this is that it started the SUBSAFE program. The bad news, the rest of the Permit (thresher) class boats all had flaws that weren’t picked up until YEARS later. My dad used to joke “you ran one drill on it, and it’d run two drills on you.”

  2. Danny Maldonado

    April 10, 2013 at 11:47 am

    Great write up brother. I’m sure I don’t need to tell you how sobering it is to think about the final moments of those men as Thresher dragged them down to the bottom with her. We’re about to toll the bells 129 times down here at NAVSEA, once for each man on Eternal Patrol…MM1(SS) sends

  3. Derek

    April 29, 2013 at 10:29 am

    This is a poignant and beautifully written essay

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