First there were the traditionalists who want to use standard anti-tank kinetic rounds. One version of this takes us back to King Kong, only instead of Curtiss F8C-4 biplanes you have A-10 Warthogs strafing the beast with their 30-mm GAU-8 cannon. This would be fine against smaller creatures, but a 500-foot beast is liable to have a protective covering measured in feet. The GAU-8's projectiles penetrate less than three inches of armor at close range (69mm at 500 meters, in fact) . They are effective against heavy tanks because they can go through side, rear or top armor, but with our beast I don't think they'd get through the skin. As someone once put it: you're going to need a bigger boat. (Or something like that).