Question: When was the last time a us submarine sunk?

Disambiguated questions and answers:
context: No context provided
question: When was the last time a us nuclear submarine sunk?
short_answers: May 22, 1968
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question: When was the last time a decommissioned us submarine sunk?
short_answers: 1 June 1971
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question: When was the last time a us submarine sunk prior to commissioning?
short_answers: 15 May 1969
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question: When was the last time a us non-nuclear submarine sunk?
short_answers: 18:57 on 29 May 1958
29 May 1958

Long-form answers:
knowledge: content: USS Scorpion, a Skipjack-class submarine, sank May 22, 1968, evidently due to implosion upon reaching crush depth. The results of the U.S. Navy's various investigations into the loss of Scorpion are inconclusive. There are various theories about the loss. All 99 men on board died. Location: 740 kilometres (400 nmi) southwest of the Azores.
wikipage: List of sunken nuclear submarines
content: USS Scorpion (SSN-589) was a Skipjack-class nuclear-powered submarine that served in the United States Navy, and the sixth vessel, and second submarine, of the U.S. Navy to carry that name.
wikipage: USS Scorpion (SSN-589)
content: On 28 May 1958, Stickleback was participating in an antisubmarine warfare exercise with the destroyer escort USS Silverstein and a torpedo retriever in the Hawaiian area.
wikipage: USS Stickleback (SS-415)
content: Bugara then operated along the Pacific coast, participating in type training and fleet exercises until decommissioned and struck from the Naval Register on 1 October 1970. While under tow near Cape Flattery, Washington, after an aborted attempt to use her as a target for USS Trigger (SS-564), the Bugara was swamped and sank accidentally. The tug was at risk of being taken down with her, so she cut the steel hawser tow cable. No crew was aboard the sub when she sank.
wikipage: USS Bugara (SS-331)
content: USS Guitarro flooded and sank pier-side prior to commissioning at Mare Island Naval Shipyard on 15 May 1969. Two shipyard teams, apparently unaware of each other's efforts, were conducting work involving filling tanks in both the forward and aft portions of the submarine. Eventually the lack of coordination led to flooding through the bow hatch.[13] The submarine was raised, but completion was delayed 32 months. Guitarro was commissioned on 9 September 1972.
wikipage: List of lost United States submarines
long_answer: Multiple U.S. military submarines have sunk over the years. The last nuclear-powered submarine to sink was the USS Scorpion on May 22, 1968. It imploded upon reaching crush depth. Sadly, there were no survivors. The last non-nuclear powered submarine to sink was USS Stickleback. It sank in a collision with USS Silverstein off Oahu on 29 May 1958. Even decommissioned subs have been known to sink. The USS Bagara accidentally sank when it was being towed back from a training on 1 June 1971. Submarines have also been known to sink before they are even used. The USS Guitarro was accidentally flooded in the shipyard on 15 May 1969. However, it was repaired and commissioned in September 1972.