I've known about the Thresher discovery part for a couple of years, but hadn't seen mention of the Scorpion.

The Thresher went down because there was a new reactor guy on board - the regular guy was sick. The new guy followed the book and shut the reactor down when a problem was signaled. The regular guy said he would probably have kept it up for awhile.

These subs don't float, they fly through the water like a shark, so with the reactor down, it started to sink. The captain tried to blow the ballast, but the air supply hadn't been dried before compressing, and the valves froze solid. This caused a change in procedures, that all compressed air had to be thoroughly dried.