USS Thresher (SSN593):
On April 10, 1963 USS Thresher (SSN593) was conducting sea trials after overhaul in Portsmouth, NH. Due to a series of unfortunate events, all hands were lost when the submarine sank. 129 sailors and shipyard personnel lost their lives that day. The incident led to a new emphasis on submarine safety. In this post, I want to pay tribute to the boat and crew, and the highlight the changes the tragedy brought to the submarine force.
According to the National Geographic, Thresher was at or near test depth when the reactor shut down. Without the power of the reactor to provide propulsion, the boat sank below its crush depth. According to reports from the USS Skylark, a submarine rescue ship accompanying Thresher, sonar operators heard a sound like air rushing into an air tank. Thresher was no more.
The cause of the reactor shutdown has not been determined. The most prevalent theory is that a seawater piping joint in the engine room failed. The water from the failed joint sprayed the electronics and forced the automatic reactor shutdown (reactor scram). According to Wikipedia, the reactor plant operating procedures at the time precluded doing fast recovery startups of the reactor plant after a scram. We practiced that evolution many times during my years aboard USS Sandlance (SSN660). Procedures also did not allow pulling steam from the plant while shutdown to drive the boat to the surface.
Additionally, the other emergency system failure was that of blowing the ballast tanks to cause the boat to surface. Anyone who watched the movie Hunt for Red October will recall the scene where USS Dallas comes flying out of the water after blowing the ballast tanks. Thresher tried to do that, too, but the design of the system failed. Instead of pumping air into the ballast tanks and blowing the water out to provide the necessary buoyancy, the condensation in the blow lines froze and stopped the flow of air. Since the boat had no power and couldn’t blow the water out of the ballast tanks, Thresher was doomed. All US submarines now have measures to prevent condensation and subsequent freezing of the blow lines.
The tragedy, one of two for the US Navy’s nuclear submarine force (the other being USS Scorpion in 1968), led to the SUBSAFE program. Wikipedia tells us that SUBSAFE is the Navy’s quality assurance program designed to maintain the safety of the nuclear submarine fleet. It provides maximum reasonable assurance that the subs hulls remain watertight and can recover from unanticipated flooding. SUBSAFE only refers to the systems exposed to sea pressure or that are critical to flooding recovery. Tight controls manage the systems. SUBSAFE materials are subject to traceability of the source material back to the lots from the mine, the smelting and hardening processes, etc. The traceability ends at the installation in a SUBSAFE system.
Admiral Rickover also changed the reactor plant operating procedures to include a Fast Recovery Startup. This allows immediate restart of the reactor plant (as noted in my comment above). Boats can also withdraw steam to get the ship to the surface in the event of emergency.
The 129 sailors and shipyard personnel who perished live on in the memories of every US Navy submarine sailor. We were and are a better, safer service for their sacrifice and we honor them on this day. RIP USS Thresher. Shipmates, rest your oars. We have the watch.