I wonder how this happened, and what kind of maneuver they were trying to perform. Those nuclear subs and ships that work with them are loaded to the gills with all kinds of detection systems that are supposed to prevent contact with enemies.
I've read of similar but different situations, like a long range bomber blowing up in a collision with the plane that was refuelling it. Or fighter planes that collided during a close maneuver drill. And then there are all the jeeps and trucks and forklifts that collided because the good ol boys were goofing off to much.