Fifty-one years ago today, on the morning of 10 April 1963, USS THRESHER (SSN-593), less than two years old and the lead boat in a new class of nuclear-powered, fast-attack submarines, began deep-diving tests about 200 miles to the east of Cape Cod, MA. The submarine-rescue ship USS SKYLARK (ASR-20) stood by overhead. At 0903 SKYLARK received a garbled transmission over the underwater telephone: THRESHER reported “Experiencing minor difficulties. …Have positive up angle…attempting to blow.” But THRESHER and the 129 men she carried—including 17 civilians—never returned to the surface.
The remains of the sub, broken up into six major sections, were eventually found scattered over a large area in more than eight thousand feet of water. After a thorough examination of photographs, objects recovered from the bottom, and records of the sub's construction and maintenance, a Court of Inquiry concluded that THRESHER's troubles likely began with the joints in her saltwater piping system, many of which had been brazed rather than welded. (Welding involves the heating to melting and direct joining of two pieces of metal, whereas brazing uses another material, one that melts at a lower temperature, to “glue” two pieces of metal together. In THRESHER's case, a silver alloy was used as “glue.”) It has been theorized that at least one of those joints failed, permitting seawater to leak into the boat and short out an electrical panel which in turn triggered a scram, or shutdown, of the reactor. Without a means of propulsion, THRESHER, gaining weight as water flooded in through the failed joint, began to sink.