The Kursk is the submarine accident I'm remembering: http://en.wikipedia.org/wiki/Russian_submarine_K-141_Kursk
And here's an article about the Thresher:
http://en.wikipedia.org/wiki/USS_Thresher_(SSN-593)
Items that might be of Brokeback Mountain interest:
Its motto was
Vis Tacita (Silent Strength) - sounds a lot like Ennis to me.
Ballard's [the man who searched for and found the Titanic] robotic survey discovered that Thresher had sunk so deep it imploded, turning into thousands of pieces.
implode - to cause to burst or collapse inward - We see Ennis collapsing inward at the lake scene
thresher - a farm machine for separating seeds or grain from the husks and straw
Things to think about...