The loss of USS Thresher SS (N) 593 on 10 April 1963

On 10 April 1963 @approximately 0900, the worst submarine peace time disaster occurred with the loss of the USS Thresher SSN 593. There were 129 precious human being lives snuffed out in an instant. These 129 men were the cream of the Navy submarine elite. Thresher was the tip of the spear for the latest, fastest most advanced submarine in the world.  It took the Navy several hours to be convinced that Thresher was totally lost with all onboard.

This submarine designed by the Bureau of Ships in cooperation with the Portsmouth Naval Shipyard had been built, christened and delivered to the Navy in August 1961.  Thresher was taken by the operating forces to demonstrate all these new capabilities and technological advances. Thresher exceeded all of the most advance expectations. As the lead ship of an entire new class of submarines to outwit and if necessary destroy enemy submarines and ships, Thresher was exposed to severe shock trials for the purpose of proving the design was truly a warship that would withstand the most severe attacks. Thresher during the operating period of almost one year had been to this new depth capability over forty (40) times without incident.

After completing a comprehensive Post Shake down Availability known as a PSA in those years, Thresher has sailed one day earlier for preliminary tests on the surface and submerged before proceeding to test depth on the second morning. Some items to consider, Thresher had been exposed to severe shock trials. The Bureau of Ships advised Portsmouth Naval Shipyard to inspect for any evidence of shock trial tests discrepancies or difficulties and correct shock test discrepancies. In addition, Thresher had been constructed with large silver braze joints in salt water systems exposed to sea pressure. The Bureau of Ships advised the shipyard to inspect all accessible silver braze joints.

The culture of the time was to protect items and not much thought was given to the possibility of losing a submarine in the depths of the sea. For example, strainers had been installed in the main ballast tank blow system to protect the valves installed from dirt and debris. In this case, the Bureau of Ships advised the shipyard to remove the strainers before sea trials. This was not done. Another item of design was to protect the nuclear reactor above all else. The main steam stop valves that supply the steam to the operating propulsion turbines and submarine turbine generators that produce the electrical power for the submarine were designed to fail closed hydraulically in the event of a reactor scram. The intent was to protect the reactor, at the time there was concern that dragging steam from a scrammed reactor could seriously damage the reactor core. There was no provision to open these valves except by manpower. The operating procedures during the time of Thresher were to follow strict rules when attempting to restart the reactor. This was time consuming and could not be done rapidly.

Some of the facts that are known from the SOSUS system that no longer exists but was an important sound surveillance operating system in the years in question detected Thresher’s reactor had scrammed. Thresher had attempted to use the Main Ballast system to recover but had difficulty. Not knowing what else had occurred, Thresher was without propulsion power, no ships power except battery power and ultimately sank to below collapsed depth.

The search for Thresher on the ocean floor confirmed the submarine did not exist but was a debris field of submarine parts, no hull sections of any form had survived.

The most advanced submarine of the day for some reason did not and could not survive whatever casualty had occurred.  However, the Navy did not step back and make the case that we sent that submarine to sea in a condition that made it extremely difficult if not impossible to survive a serious casualty. We denied the submarine propulsion power to drive the submarine to the surface, we denied the submarine an adequate blow system to rise to the surface and we sent a submarine to test depth the first time following shock trials without assuring that all serious deficiencies had been located and corrected.

Those 129 men lost on Thresher did not die in vain, the Navy reexamined and reviewed the entire design, they instituted the Submarine Safety Program and following much soul searching changed the configuration of the Main steam stop valves.  This followed reactor plant testing that demonstrated it was safe to drag steam from the reactor for twenty minutes without damaging the reactor core. The Navy created the Submarine Safety Center to be a continuing oversight organization.  The Navy continues to vigorously follow the rules to insure we keep our submarines as safe as humanely possible recognizing they are warships and must be battle ready.

Today’s submarines are significantly safer and much more advanced than Thresher.

About the Author

Joseph F. Yurso, Captain USN (retired), is currently Director of Technical Development for Q.E.D. Systems Incorporated of Virginia Beach, Virginia. He has been with Q.E.D. for over 30 years.  Mr. Yurso has been a member of the American Society of Quality since 1989 and was a founding member and past chairman of the Tidewater section. Other positions Mr. Yurso has held include National President of the American Society of Naval Engineers. He is a past President of the American Maritime Modernization Association (AMMA).  Mr. Yurso began his career as a commissioned officer serving 30 years in the United States Navy.

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