As a captain of the extraterrestrial defense forces you embark on an all-out fight against a multitude of enemies. Your objective is to avoid at all costs that the enemy troops cross the atmosphere and reach the Earth. The objective of the player is to prevent the enemy ships from reaching the left side of the screen. The player has a very powerful weapon capable of destroying enemy ships in one hit, but the drawback is that he can only fire one shot at once. The player can move up and down and must choose the precise moment to fire his weapon.