What you have to do is name the battleship and then make a new script. Click on structure, unmanned and then select whatever you've named it. Now you can put infantry inside.
for one, you cant unman a structure... if its unmanned it neutral... so just make it neutral team... secondly, the aircraft carrier is a building afaik, so making it unmaned wont help, youd need to make it capturable through map.ini, but heres something to think about, aircraft carrier = naval, how on earth are you gonna get a guy into it either way?