Earth is under alien attack! The player is the sole defender and has to keep the alien ships from reaching their destination by ramming them. Despite the game being technically turn-based, the result is an action game: each round is on a timer and at the end of the time span, all enemies move one field - even if there was no player movement. The round also ends when the player moves with the result that, at least on the lower difficulty levels, a fast enough pace can keep the enemies on their place. The game field (one screen) is filled with different ASCII characters which represent the game's objects: the player's ship, alien ships (are taken out of the game when touched), droid ships (deadly by touch), meteors (deadly for both the player and enemies), Earth and stationary mines (also deadly). The game ends when either all alien ships are gone, an alien ship reaches Earth or when the player dies. There are nine difficulty levels which determine the length of a round.