Every US submariner cites Thresher as the reason for perfect maintenance.
SUBSAFE.
It was the constant refrain at the plant.
USS Patrick Henry SSBN 599N
The Patrick Henry was based on a similar hull. My training when I was in ‘68-73 told a different story. Sonar from the time said that ice formed in the MBT blow valves aft and the boat developed a large up angle. In order to save the boat the forward MBT valves were opened and the boat then because the aft MBT tanks still had some air in them they developed a large down angle. The up angle earlier scrammed the reactor and within a couple minutes steam pressure for a full bell was lost. Loss of propulsion, the boat was trimmed heavy now that speed was reduced. Blow was attempted again and again the aft MBT valve(s?) froze and they developed an up angle spilling air out of forward tanks from which they couldn’t recover and they went down aft first. Could have been some other failure that caused the MBT blow but without ice they should have been able to recover. HI-Pacs (High pressure air compressors) had water seperators but there was always a little moisture and going from 3000PSI to 40PSI or less will sure bring out the moisture and freeze it pretty quickly.
This is what mandated the “Sub Safe” program. One of the biggest things to come from that was an emergency MBT blow system that could be overridden manually with huge knocker handvalves. The valves were so large they were very unlikdly to be bothered by ice.
There are always safety issues on any instrument of war. A submarine is an unbelevibly complicated weapon. We may not know what caused them to blow but we know what caused the sinking.