This Dead U.S. Navy Nuclear Attack Submarine Is a Legend for a Very Simple Reason

WE studied the failures of Thresher quite a bit in Nuke School and Sub school...

Out of 66 submarines lost, The Thresher holds a very dear spot in the hearts of all submariners.

Some people only count 65 submarines...however, the Tolling for the Boats Ceremony often includes one other submarine out of our history: The Allligator, lost in 1863 while under tow around Cape Hatteras.

44 were lost with all hands.
15 were lost with some survivors.
7 were lost with no loss of life.

The USS Thresher holds a special spot for several reasons, but the three biggest are:

- First, she was not lost due to combat. While all losses are tragic, this makes hers even more so.
- Second, her loss directly resulted in the creation and institution of the SUBSAFE program, which is still rigorously adhered to today, more than half a century later.
- Third, how the reactor plant is operated during flooding casualties was changed.

So, what happens when a submarine sinks like the Thresher did?

The ship would have been rigged for deep diving. All compartment hatches would have been shut. A careful, planned descent to test depth was in progress. (And no, I can't confirm nor deny what the test depth was. About all I can say is that sources like Wikipedia place that at 1,000 feet.) Reports say that the ship likely imploded at 1,300 to 2,000 feet.

A flooding casualty appeared to have been in progress, according to prevailing theories. They communicated a "minor difficulties, have positive up-angle, attempting to blow". Shortly afterwards, "900" came across on a garbled message. Here's a brief description of what the crew would have been doing during a flooding casualty:

For flooding aft, the casualty would have been announced and a ship-wide alarm sounded. The crew would have immediately performed a sequence of actions as follows, while all off-watch personnel would have immediately executed their training for combatting the actual flooding. Flood control would have been actuated to attempt to stop the flooding by shutting sea water hull valves. An Emergency Blow of all main ballast tanks would have been attempted due to the loss of propulsion. An attempt to restore propulsion by any means would have been made in order to drive the ship to the surface.

Likely, the crew would have been far too busy to dwell on their impending doom...which is a blessing. Because this is what happened:

The ship sank deeper, with hull pressure increasing about 45 pounds per square inch with each 100 feet. At 900 feet, the assumed depth the ship was at when they received the garbled message which included "900", pressure on the hull would have been about 400 pounds per square inch. That's 57,600 pounds per square foot, or 28.8 tons.

If you assume the hull collapsed at 2,000 feet, that would have been 900 pounds per square inch, or 129,600 pounds per square foot (64.8 tons). Consider this: a diesel engine operates at about 16:1 compression, or 234 psi. At this pressure, the temperature increase is high enough to ignite diesel fuel. The hull pressure was about 4 times this at the time of collapse.

When the hull collapsed at those pressures, death was instantaneous for every Sailor aboard. There were no "drowning deaths", no prolonged sufferings, no compartment which could have provided any shelter or protection.

Out of 66 submarines lost at sea, THIS is the one which gave us SUBSAFE. THIS is the one which changed the paradigm on propulsion plant operation during flooding casualties. THIS is the one where the survivability of all future (and then existing) submarines took a quantum leap ahead.

And 129 people died to give us that. 113 fellow shipmate, 13 shipyard workers, and 3 officers as observers.

God rest their souls.

Thank you for the interesting read on the Thresher.