Space Invasion Tower Defense

Space Invasion Tower Defense: How long can you last the invasion in this strategy game? Purpose of Game: Strategically place towers on the game map in order to defend the gem. At the end of each wave you earn interest on your money earned. Use it to buy and upgrade towers in order to make it through wave after wave of enemy ships. How to Play: Drag and drop towers to defend against incoming spaceships. Special Tricks for Gameplay: There are twelve towers to choose from, but you can't build an unlimited amount of the 'Ultimate Tower.'