Defend your base against incoming enemies that attack with rockets, parabombs, jets and helicopters. Make sure no one breaks through your line of defense!
Testing piercing rockets - a piercing rocket is a shot that's counted as a direct hit (destroying an enemy with impact force and not via explosives).
Piercing shots penetrate the enemy and continue to fly and explode when hitting other enemies. It's a technology upgrade though and must be unlocked through playing.