I remember. I was 14 at the time and in the habit of listening to Jean Shepard's program on WOR radio from New York before going off to sleep. There was a news bulletin. The Navy was reporting one of its submarines as overdue at Portsmouth Navy Yard. A search was underway. I had no understanding of abyssal deeps and vast pressures, and so I went to sleep with hope. As I'd understand in future years, my hope was unjustified.
I really didn't think very much about Thresher until eight years later, in the summer of 1971 when I went to work as a design engineer at the Electric Boat Division of General Dynamics Corporation. Immediately, I was plunged into the design effort to incorporate modifications known collectively as SUBSAFE on the forthcoming second overhaul of the Lafayette class of ballistic missile submarines. The work embodied in the SUBSAFE program was the direct result of the loss of Thresher.
There are two aspects to SUBSAFE. One is an intensive quality assurance regime encompassing both materials traceability and rigid process controls. The other involves improvements in systems design to ensure that the casualties that are inferred to have led to the loss of Thresher can never again have similar consequences.
Based on the painfully limited evidence, those investigating the ship's loss concluded that the precipitating casualty was the failure of a seawater pipe joint in one of the ship's machinery spaces. The crew was unable to secure the inflow of seawater from this failure. The intense spray, driven by the pressure of the sea at or near Thresher's design depth, would have penetrated electrical control panels and caused the loss of propulsion. (NB: Recently a countervailing theory has emerged which posits that the seawater piping failure is neither likely nor necessary to account for the loss of the ship. The sinking, it holds, could have followed from loss of propulsion due to an electrical casualty compounded by a failure of the ballast tank blow system.)
At the time, the design and operation of the nuclear propulsion plant was governed by a philosophy that focused on saving the reactor at any cost. So any disruption of control circuitry would cause an immediate reactor plant shutdown. But this deprived the ship of the ability to use hydrodynamic forces against the effects of the flooding casualty. Would a few more minutes of propulsion have made a difference? We'll never know.
The last hope would have been use of the ship's high pressure air banks to blow the main ballast tanks on an emergency basis. Testing later showed that the rapid flow of air through the system would have caused plummeting temperatures and formation of ice that would block the piping and prevent the air from reaching the tanks. With no way to deballast, no propulsion, and no way to secure the flooding, Thresher was doomed.
With the adoption of this scenario as "probable cause", the SUBSAFE program set out to address each stage of the cascade of casualties. The quality assurance aspects sought to ensure that all seawater piping systems could always withstand the pressures of the deep. But if that failed, hydraulic remote valve actuation systems were installed (that was the piece of the puzzle I worked on) to ensure that hull and backup seawater valves could be shut to secure flooding. And last, the Emergency Main Ballast Tank Blow system was completely redesigned to ensure that it would be effective under all circumstances.
Outside of the bounds of SUBSAFE, the design and operating philosophies of the Naval Nuclear Propulsion Program were modified to allow ships to maintain propulsion as long as possible in the event of a casualty even if damage to the reactor is a possibility.
Did SUBSAFE accomplish its mission? The evidence says that it did. From 1915 until the loss of the Thresher sixteen US Navy submarines were lost to non-combat causes. Afterward, the only such loss was that of Scorpion in 1968. That ship was not yet SUBSAFE certified.
I am proud to have been involved in a modest way in the implementation of SUBSAFE. And I hope that the surviving relatives and friends of those lost aboard Thresher 50 years ago can find solace in the fact that their loss led directly to a profound reduction in the risk of submarine operations.
Eternal Father, Strong to save,
Whose arm hath bound the restless wave,
Who bid'st the mighty Ocean deep
Its own appointed limits keep;
O hear us when we cry to thee,
for those in peril on the sea.