OBJ: Destroy Bridge
One team must destroy a bridge and make sure it stays destroyed.
OBJ: Defend Bridge
The other team has to keep the bridge up.
OBJ: Retrieve Asset
The fiendish enemy have captured a tank/chopper/whatever, get it back!
You get the idea. A map could have several different objectives that need to be completed to win (perhaps in a set order?), so they can be big or small tasks. Be creative, lets have some ideas!
