As far as I', concerned, in RP anyone should be able to fly a properly set up ship of a faction that is gunboat or lower.
Factions given a limited right to restrict cruiser class vessel. (Basically the right to make them change the name if it makes no sense, like naming a military cruiser "Banana-spit", or try to "Re-posses" the ship if it shows poor RP)
And Fully fledged battleship need faction approval.
I'd even go for cruiser to be stuck into the same restriction class as gunboat, but I rally thing Battleships should have faction control.
