PROTECTION OF THE EARTH'S BASE

Many years have passed since then, as our once blue planet has become so deplorable. Endless war and alien invasion have left chances of survival of the former nature. Well, You need to protect what is left. The aliens are trying to destroy Your earthly base, so immediately jump on the defensive. Shoot at all units of the enemy and prevent they flew to the base of the shot distance. In Your database, however, a fair stock of weapons, which can be connected gradually, level by level, earning money. The enemy, of course, also will strengthen the attack and weapons. Very solid and interesting shooter.