Inspired by Atari's Breakout, the game itself resembled an adaptation of the popular shooting gallery games that were a mainstay of carnivals. In this electronic version of the game, the player controlled the motions of a movable laser cannon that moved back and forth across the bottom of the video screen. Rows and rows of video aliens marched back and forth across the screen, slowly advancing down from the top to the bottom of the screen. If any of the aliens successfully landed on the bottom of the screen the game would end. The player's laser cannon had an unlimited supply of ammunition to shoot at the aliens and destroy them before they hit the bottom of the screen.
Meanwhile, the aliens would shoot back at the player, raining a hail of deadly rays and bombs that the player would have to dodge lest his cannon be destroyed. The player's cannon could be destroyed three times (the player had three lives), and the game would end after the player's last life was lost. Occasionally a bonus spaceship would fly across the top of the screen which the player could shoot for extra points.
As the player destroyed an increasing number of aliens, the aliens began marching faster and faster, with the lone remaining alien zooming rapidly across the screen. Shooting the last alien in the formation rewarded the player with a new screen of aliens, which began their march one row lower than the previous round.