Cannon

Warning! Your palace is under attack and it's an air raid! Enemies flying bombardiers are hovering above your palace in high speed and drop a bomb each time they passed on top of the palace and each bomb will certainly cause damage. As the head of the palace guard, it is your duty to stop this attack and protect your palace. Unfortunately, you do not have any air units of your own. Fortunately, you do have one recently installed super cannon at your disposal. This super cannon is so awesome because it can be reloaded in almost an instant and it can be rotated vertically 180 degree, making it possible to aim for any enemies' airborne units. Also, unlike a normal cannon which has a somewhat fixed shooting range, this super cannon has a mechanism to control how far will the round go when fired. This means you can very much time and control every aspect of the cannon shot. So aim fast and shoot fast because the enemies are flying high speed. Just remember that you should not allow too many bombs to be dropped on the palace because if your palace has sustained too much damage, your king will become disheartened and wave the white flag of surrender. If that should happen, it means that you are a total failure. Are you ready? Aim... Fire!