Inspired by Taito's earlier electromechanical machine Space Monsters[4] and Tomohiro's interpretation of alien descriptions in War of the Worlds,[1] the game itself resembled an adaptation of the two. In this video game 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. Although the player's laser cannon had an unlimited supply of ammunition, it could only fire one shot at a time.