When waiting for a retaliatory strike a sub can be at any operational depth, it doesn't have to wait at firing depth near the surface. It could potentially be a

When waiting for a retaliatory strike a sub can be at any operational depth, it doesn't have to wait at firing depth near the surface. It could potentially be a kilometer below the surface. If some hearsay is to be believed it could be resting on the ocean floor. There is also the matter of targeting these things. Water absorbs radar and if they are silent you have no way to target your bunker buster.