At 9:18 a.m. on April 10, 1963, sonar operators aboard the U.S. Navy submarine rescue ship Skylark, which
was accompanying the nuclear attack submarine Thresher, heard a chilling sound like air rushing into an air tank,
and Thresher was no more. Its deep-dive trials southeast of Cape Cod, Massachusetts, had come to a cataclysmic end
and all 129 men aboard perished in 8,400 feet (2,560 meters) of water.
Five minutes prior to the implosion, Thresher had radioed that it was having minor problems. Skylark received several fragmentary,
garbled messages, followed by silence. Moments later the chilling sounds of a submarine breaking apart and imploding were heard.
According to U.S. military reviews of the accident, the most likely explanation is that a piping joint in a sea water system in the
engine room gave way. The resulting spray shorted out electronics and forced an automatic shutdown of the nuclear reactor.
When the accident occurred, Thresher was near its maximum test depth, which, though classified, was probably around
1,300 feet (396 meters). Most submarines are built to survive down to a crush depth, which can be 20 to 35 percent greater than
their maximum test depth. However, without the reactor, the sub would not have had enough power to stop itself from sinking to
As they sank, the men aboard would have heard piping and fittings giving way. They would have listened as the ships
hull creaked and groaned, until it finally, deafeningly gave way to massive water pressure. All lives were likely extinguished
within a matter of seconds.
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