I spent four years stationed on a nuclear submarine. It can be a lonely job in the most isolated environment you can imagine.
The Russian submarine Kursk went down a few years ago. All hands died. Many of them died a long, slow, painful death.
There is currently another Russian submarine on the bottom, it is a min-sub and has a crew of seven. The crew is still alive; but, they only have enough air for 24 more hours.
I hope they can be rescued, that would be a terrible way to die.