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 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).