Your mission in this shooting game is to fire away at the enemy units crossing your screen. Try to put them down before they can harm the building. To keep up with the ever increasing number of enemies you must use your money wisely and buy the right upgrades. If your building is damaged it is smart to spend some money on repairs. Use YOUR MOUSE to aim and fire. Press and hold SPACEBAR to zoom in. Use "D" and "F" KEYS to switch between weapons. Press "R" KEY to reload. Good luck!