NATIONAL DEFENSE

A tower defense game. You are the commander of the UN armed forces, in the future, an alien invasion has put the fate of the human race in jeopardy. If aliens make their way to the surface of the Earth, people are doomed. We'll have to stop them through a system of orbital fortresses in space.
Build a deadly defense and don't let the aliens break through your cordon.

There are 5 types of towers available to you, each of them specializing in a specific role. You can sell the tower for 75% of its value to get emergency reserves of resources.
To start the invasion, click on the start label. The next waves will be assigned to a timer, but you can run them faster for extra resources.
Do not forget to upgrade the towers in time, they must grow to the maximum in terms of fire power, power and firing range, otherwise you simply cannot cope with many enemy vehicles!