Saying we need it because we used to have it is not going to win this battle. A need has to be proven and if that is difficult, it may be as a result of the need not actually being there.
Well assuming that the Russians are modernising their surface & submarine fleets purely for peaceful reasons then you have a valid point. Oh, & of course the ever increasing Chinese navy is purely decorative. Maybe as junior partner to the US Cameron will rely solely on our special relationship to get us out of any future hole. After all he seems to think that's what happened in World War II!
