Aliens have landed on the earth, and are trying to occupy a medieval fort.
You have to shoot down these aliens to prevent them from occupying the fort.
If the number of aliens occupying the fort exceed twenty the game ends.
If you complete five levels you win the game.
The number of hits required to kill an alien increases by one at every level.
At the end of every level you have to update the game by converting the aliens inside the fort into your weapons, provided you have enough money.
Drag the cursor to aim at the red dot on the alien, and click the mouse to shoot.
Click the space bar to release your converted weapons from the fort.