mostly - everything with a powersupply of 7.000.000 - thats dreadnaughts, juggernaut, battlestars, battleships, carriers.
you ll know that its a battleship when you see the gaping hole in your purse after you purchased one. anything less than a battlehip is significiantly cheaper. cruisers are around 200 mio .... battleships around 400-500, i think. battlecruisers are cruiserclass, even if they can mount a few lvl10 turrets.