Here's what lets me sleep at night: Nuclear-armed Trident submarines. The world knows they exist, but no one knows where they are at any given moment. That and the nuclear processing signature will tell us where those weapons are built and who to retaliate against.
However, I can see a conventional naval war with China if they move on Taiwan. We will lose a lot of sailors, but they will lose the war due to our training and experience. They can build as many platforms as they like, but our Naval Aviators are second to none.
The MAD theory still applies if we’re attacked by an identifiable nation. What happens when a missile is fired from a container on a Monrovian registered ship in the gulf? What nation do you turn to glass, Monrovia? Where’s the deterrence for a non state terrorist or a third party terrorist state. I don’t worry about China or Russia, as they’ve much too much to lose. That’s what’s so terrifying.