Your mission is to destroy the alien fortresses and save the planet Earth from certain annihilation.

The fortresses are heavily armed satellites placed in orbit around the Earth. They possess tremendous amounts of energy which is channeled into a planet-warping magnetic field. Each fortress derives its energy from a Magnetron Generator.

You attack by flying your Photon Fighter over the surface of the fortresses while bombarding the alien's defense cannons with your own particle beam weaponry. If you knock out all the cannons, the Magnetron Generator will short-out and the fortress will be destroyed. When the cannons are firing back at you, you may protect yourself with a shield around your Photon Fighter. Your Photon Fighter can withstand a few unshielded hits from the enemy cannons, but it takes a lot of fuel to absorb the energy (2000 units per unshielded hit).

As you fly over the surface of a fortress, the magnetic forces you must contend with can be very unpredictable. The force they generate may push you or pull you, you'll never know until it hits you. Sometimes you may be able to nullify the magnetic force by knocking out the Magnetron Generator itself with a direct hit.

The walls of a fortress also have unpredictable properties. Sometimes your Fighter will bounce off a wall, sometimes it will pass right through a wall. Sometimes when you hit a wall your Fighter will explode from the impact. There's only one way to know what kind of wail you face before it's too late: fire on the wall and see what happens.