The action is viewed from a fixed, single-screen perspective. Alien rows move horizontally, descend when they reach a screen edge, and become faster as their numbers decrease. The objective is to clear each formation while avoiding enemy shots and preventing any invader from reaching the bottom.

The player moves the cannon from side to side and fires upward. Defensive barriers can absorb some shots, but they deteriorate as they are hit. Success leads to another formation with the same basic objective, while a larger alien may occasionally cross the top of the screen for bonus points.

Stay near the center when possible so the cannon can respond quickly to either side. Clear lower aliens first: they are the immediate threat and their removal also makes the remaining formation move faster.

Use shields as temporary cover rather than permanent protection. Fire deliberately, watch the gaps in the enemy formation, and prioritize incoming shots. When the formation is nearly cleared, keep moving because its increased speed makes late-stage mistakes more likely.