Thresher was the one that sank because ice formed in her valves right? They came to that conclusion because one of the sisters had a very close call with the same issue when trying to do an emergency blow.
Scorpion was the one surrounded by conspiracy theories right?
Thresher was conducting deep dive trials off New England on April 10, 1963; the test procedure was to descend to her test depth (given as 1,300 ft) in 100-ft increments while circling slowly under the submarine rescue vessel
Skylark to maintain communications on her underwater telephone (a.k.a. "gertrude"). Close to test depth
Thresher transmitted a garbled message at 9:13 interpreted as "... minor difficulties, have positive up-angle, attempting to blow," and then another garbled transmission at 9:17 which has been reported as including "exceeding test depth." Shortly after 9:18 am both
Skylark and the SOSUS listening network reported a sound consistent with an implosion, and afterwards
Skylark was unable to regain communications.
The wreck was not fully located until the following year; five large sections were found within a debris fiedl covering about 33 acres at a depth of 8,400 ft. The inquiry at the time focused on seawater piping in the sub that was silver-brazed rather than welded at the joints; prior testing had found deficiencies in 14% of these joints although most were considered noncritical. However, two failures of silver-brazed pipe joints on other subs had occurred previously; one of these was on the diesel-electric submarine USS
Barbel near her test depth and had admitted an estimated 18 tons of water into the engine room in the three minutes it took for the submarine to blow her ballast tanks and get to the surface. The hypothesis was a similar casualty had occurred on
Thresher and shorted out electrical systems which caused an automatic shutdown of her reactor. Under then-current procedures it would have taken 10 minutes to restart the reactor. Later testing on
Thresher's sister ship USS
Tinosa showed that moisture in the sub's air flasks could cause the valves to freeze up in seconds when an emergency blow was ordered; it's believed this happened to
Thresher and doomed the sub. The SUBSAFE program was instituted afterwards to address those issues; as the saying goes the regulations are written in blood.
USS
Scorpion (SSN-589) was an older
Skipjack-class nuclear sub that went missing in May 1968; she had been overhauled at Charleston Naval Shipyard the previous year but due to the additional length of time required for SUBSAFE overhauls (what before had been 9-month yard periods were now 40 months due to shortages of parts and increased quality-control checks), she was given a reduced overhaul that deferred many of the SUBSAFE requirements (in particular, fixes to the emergency blow system).
Scorpion was deployed to the Mediterranean afterwards; she was reportedly restricted to a maximum dive depth of 500 ft given her non-compliance with SUBSAFE.
Scorpion departed the Med on May 16, 1968, subsequently stopping at Rota in Spain to drop off two crew and escort a ballistic missile submarine out of port. Afterwards she was ordered to monitor Soviet naval activity near the Azores; the sub's last message was that it was en route on May 21. She was reported overdue six days later.
Scorpion's wreck was found at the end of October 1968 at a depth of 9,800 ft; while the bow was generally intact the aft end of the sub had telescoped forward into the midships section approximately 50 ft, breaking the hull in half and shearing off the sail. As with
Thresher, there were sound recordings from distant listening stations, but with no eyewitnesses there have been a lot of conspiracy theories. Several plausible hypotheses including an explosion of the sub's batteries or an explosion of a torpedo battery (the Mark 37 torpedoes used at the time had experienced battery fires) have been raised.
