Our current Navy completely dwarfs any other country's naval fleet. Hell, it's not even a fair comparison at all - kind of like comparing Mt. Everest with Mt. Rushmore.
You have to ask yourself why would we need even MORE ships? Why do we even need as many as we have now?
There is one reason, and one reason ONLY: EMPIRE
This is the only rational reason any country would need a navy so large, in order to project their interests around the entire world. With our current navy, we can simultaneously maintain a presence in Europe, the Middle East, Southeast Asia, the Far East, as well as closer to home.
There is no other reason that we would need to have such a large naval force.