Seriously, massive guns, lots of them, advanced air defenses, massive armor that could take hits.. and lots of them.
Call them sea-hulks for all their raging raw power (damn that just sounds cool).
and yes, it'd scare the crap out of anyone thinking about messing with us.
"Seriously, massive guns, lots of them, "
What you really want are the new generation railguns that are kinetic energy devices you can maybe rapid fire if you have a big electrical plant.