9 April 1963, after the completion of this work, Thresher, commanded by
Lieutenant Commander John Wesley Harvey, began post-overhaul trials.
Accompanied by the submarine rescue ship Skylark, she sailed to an area some
220 nautical miles east of Cape Cod, Massachusetts, and on the morning of 10
April started deep-diving tests. As Thresher neared her test depth, Skylark
received garbled communications over underwater telephone indicating "...
minor difficulties, have positive up-angle, attempting to blow." When
Skylark received no further communication, surface observers gradually realized
Thresher had sunk. Publicly it took some days to announce that all 129
officers, crewmen, and military and civilian technicians aboard were presumed