Stronghold

During one of your deep-space patrols, you discover an abandoned base whose self-defense systems are still operational. When the base detects your presence, it launches waves of drones to destroy you. After you defeat three attack waves, a three-layer force field forms at the bottom of the screen to protect a SAM crawler. Your objective is to shoot an opening through the horizontally moving force field and destroy the SAM crawler while hostile drones continue their attack. Once you breach the force field, you must avoid being shot down by the SAM crawler, which takes advantage of the damage you inflicted on its defenses. The game features 16 variations. Some allow rapid fire, while others make the attack drones invulnerable to your missiles or create drones that clone themselves. Other variants generate a force field that descends from above, gradually reducing the space available for movement.

In Stronghold, a deep-space patrol leads you to an abandoned base whose automated defenses deploy waves of hostile drones. Survive the attacks, breach the moving force field protecting the SAM crawler, and destroy the weapon while adapting to variations featuring rapid fire, cloning drones, invulnerability, and shrinking movement space.