Thresher Submarine

* The USS Thresher (SSN-593) was the lead boat of her class of nuclear-powered¬† attack submarines in the United States Navy. She was the U.S. Navy’s second submarine to be named after the¬† thresher shark. On 10 April 1963, Thresher sank during deep-diving tests about 220 miles east of Cape Cod, Massachusetts, killing all 129 crew and shipyard personnel aboardd. Her loss was a watershed for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as SUBSAFE. The first nuclear submarine lost at sea, Thresher was also the third of four submarines lost with more than 100 people aboard.

* Created to find and destroy Soviet submarines, Thresher was the fastest and quietest submarine of its day, matching the smaller, contemporary Skipjack class. She also had the most advanced weapons system, including launchers for the U.S. Navy’s newest anti-submarine missle, the SUBROC, as well as passive and active sonar that could detect vessels at unprecedented range. Shortly after her loss, the Commander of Submarine Force Atlantic wrote that “the Navy had depended upon this performance to the extent that it had asked for and received authority to build 14 of these ships, as well as an additional 11 submarines with very much the same characteristics. This was the first time since World War II that we had considered our design sufficiently advanced to embark upon construction of a large class of general-purpose attack submarines.”

* During her development Thresher undertook operations supporting development of the SUBROC anti-submarine missle. She returned briefly to New England waters after which she proceeded to Florida for more SUBROC tests. While moored at Port Canaveral, Florida, the submarine was accidently struck by a tug, which damaged one of her ballast tanks. After repairs at Groton, Connecticut, by the Electric Boat Company, Thresher went south for more tests and trials off Key West Florida, then returned northward. The submarine entered Portsmouth Shipyard on 16 July 1962 to begin a scheduled six-month post-shakedown availability to examine systems and make repairs and corrections as necessary. As is typical with a first-of-class boat, the work took longer than expected, lasting nearly nine months. The ship was finally recertified and undocked on 8 April 1963.

* On 9 April 1963 Thresher started her initial post-overhaul dive trials, in an area some 220 miles east of Cape Cod, Massachusetts. That afternoon, Thresher conducted an initial trim-dive test, surfaced, and then performed a second dive to half of her 1,300-foot test depth. Before she entered the yard in late 1962, the Tresher had been to her test depth about 40 times. She remained submerged overnight and re-established underwater communication with Skylark…the rescue ship…at 6:30 a.m. on 10 April to commence deep-dive trials. Following standard practice, Thresher slowly dove deeper as she traveled in circles under Skylark-to remain within communications distance-pausing every 100 feet 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”. When Skylark received no further communication, surface observers gradually realized Thresher had sunk.

* Deep-sea photography, recovered artifacts, and an evaluation of Thresher’s design and operational history permitted a court of inquiry to conclude that the submarine had probably suffered the failure of a salt-water piping system joint that relied heavily on silver brazing instead of welding. Earlier tests using ultrasound equipment found potential problems with about 14% of the tested brazed joints, most of which were determined not to pose a risk significant enough to require repair. But on 30 November 1960, nearly three years prior to the accident, USS Barbel suffered such a silver-braze joint failure near test depth when on an exercise, flooding the engine room with an estimated 18 tons of water in the 3 minutes it took to surface under power and with blown tanks. This incident was followed months later by more silver-braze failures aboard the ballistic missle submarine USS Abraham Lincoln during trials.

* Hign-pressure water spraying from a broken pipe joint may have shorted out one of the many electrical panels, causing a Shutdown(“scram”) of the reactor which in turn caused Thresher’s loss of propulsion.



* Which supports and barriers were in play?

* What were the dynamics?

* Who, or what, won the Tug-of-War?

* Discuss the outcome with your friends and family.

* Use Post #4 as a reference for the dynamics, and the relationships, between supports and barriers.