USS Thresher (SSN-593) was lost at 09:15R April 10th, 1963 with all hands during her last dive to test depth, imploding after passing through crush depth.
On 9 April 1963,
Thresher, commanded by
Lieutenant Commander John Wesley Harvey, got underway from Kittery, Maine at 08:00 and met with the submarine rescue ship
Skylark at 11:00 to begin her initial post-overhaul dive trials, in an area some 220 mi; 350 km (190 nmi) east of
Cape Cod, Massachusetts. That afternoon
Thresher conducted an initial trim dive test, surfaced, and then performed a second dive to half of test depth. She remained submerged overnight and re-established underwater communications with
Skylark at 06:30 on 10 April to commence deep-dive trials. Following standard practice,
Thresher slowly dove deeper as she travelled in circles under
Skylark – to remain within communications distance – pausing every 30 m (100 ft) of depth to check the integrity of all systems. As
Thresher neared her test depth,
Skylark received garbled communications over
underwater telephone indicating " ... minor difficulties, have positive up-angle, attempting to blow", and then a final even more garbled message that included the number "900".
[8] When
Skylark received no further communication, surface observers gradually realized
Thresher had sunk.
By mid-afternoon, 15 Navy ships were en route to the search area. At 18:30, the Commander, Submarine Force Atlantic, sent word to Portsmouth Naval Shipyard to begin notifying the crew's family members, starting with Commander Harvey's wife, Irene Harvey, that
Thresher was missing.
By morning on 11 April, all hope of finding
Thresher was abandoned, and at 10:30, the Chief of Naval Operations Admiral
George W. Anderson Jr., went before the press corps at
the Pentagon to announce that the submarine was lost with all hands. President
John F. Kennedy ordered all flags to be flown at half staff on 12–15 April in honor of the 129 lost submariners and shipyard personnel.