Hmm. If we have two stealth submarins on secret missions out there, there is a risk they collide. The reason for having a stealth sub on secret mission is to gain surprise capability and potential.
Unfortuately we need some sort of co-ordination of the missions to avoid the collision. And that co-ordination reduces the surprise potential, since more people know about the missions.
So. What went wrong when a french and english submarine collided? (http://edition.cnn.com/2009/WORLD/europe/02/16/british.french.submarine.incident/index.html