Date of Loss: 10 April, 1963
Returned to Service: No
Sank off New England coast while on sea trials following an overhaul. The exact cause is unknown. A Navy board of inquiry determined that the "most likely cause" was a failure in either a pipe, a pipe valve, or a hull weld, causing flooding somewhere near the engine room.
The flooding probably short-circuited an electrical system related to the main engine, causing the reactor to "scram" or shut down. Without power, the Thresher was unable to surface, and the continued flooding caused Thresher to drop below her crush depth where the pressure of the ocean destroyed her.
129 men lost, no survivors.
(9 officers, 85 crew,
18 Navy technicians, and 17 civilian contract technicians)
Return to The Early Cold War
Return to Peacetime Submarine Accidents
The loss of the Thresher led to the development of the "Subsafe" program. "Subsafe" increased reserve buoyancy, thus making it easier for a submarine to rise to the surface despite damage or flooding. It also changed the valve control system, allowing all valves to be easily shut off from the control room.
It should be noted that failures of through-hull fittings are not unheard of, especially during test-depth dives (which is the reason, after all for such tests.) U.S.S. Growler (SSG-577) suffered just such a failure on 5 November, 1958, during her post-commissioning sea trials (while just 75 feet shy of her test depth.) In Growler's case, the temporary blank covering an unused cable fitting in the forward sonar room failed, leading to serious flooding. "Emergency Surface" was ordered, and Growler was able to surface, albeit with a forward down angle. However, she suffered only superficial damage, and was able to complete her sea trials and begin her operational career.