Was the tragic sinking of the USS Thresher (SSN-593)

"Measured by lives lost, historic context and significance, the
sinking of Thresher was then, and remains today, the world's worst
submarine disaster. As the first nuclear submarine lost at sea, its
disappearance generated international shock and sympathy."

http://en.wikipedia.org/wiki/USS_Thresher_%28SSN-593%29