The game is played by moving a crosshair across the sky background via a trackball and pressing one of three buttons to launch a counter-missile from the appropriate battery. Counter-missiles explode upon reaching the crosshair, leaving a fireball that persists for several seconds and destroys any enemy missiles that enter it. There are three batteries, each with ten missiles; a missile battery becomes useless when all its missiles are fired, or if the battery is destroyed by enemy fire. The missiles of the central battery fly to their targets at much greater speed; only these missiles can effectively kill a smart bomb at a distance.
The game is staged as a series of levels of increasing difficulty; each level contains a set number of incoming enemy weapons. The weapons attack the six cities, as well as the missile batteries; being struck by an enemy weapon results in the destruction of the city or missile battery. Enemy weapons are only able to destroy three cities during one level. A level ends when all enemy weaponry is destroyed or reaches its target. A player who runs out of missiles no longer has control over the remainder of the level. At the conclusion of a level, the player receives bonus points for any remaining cities (50 points times scoring level, 1 to 6, first 254 levels; 256, levels 255 & 256) or unused missiles (5 points times scoring level, 1 to 6, first 254 levels; 256, levels 255 & 256). Between levels missile batteries are rebuilt and replenished; destroyed cities are rebuilt only at set point levels (usually per 8,000 to 12,000 points).
The game inevitably ends when all six cities are destroyed, unless the player manages to score enough points to earn a bonus city before the end of the level. Like most early arcade games, there is no way to "win" the game; the game keeps going with ever-faster and more prolific incoming missiles. The game, then, is just a contest in seeing how long the player can survive. On conclusion of the game, the screen displays "The End", rather than "Game Over", signifying that "in the end, all is lost. There is no winner".[4] This conclusion is skipped, however, if the player makes the high score list and the game prompts the player to enter their initials.