Aliens are trying to take over the world. It's your job to stop them - so you climb into your trusty chopper, the Viper, and fight your way through many alien-infested levels to the base of the enemy.
Viper is a fast-paced non-stop shoot 'em up action game. You fly through the levels with your chopper on a pre-set route with only a few junctions where you may choose the path to go; the entire screen will (especially in the later levels) be filled with bullets and explosions. Lots of add-on weapons may be picked up to improve your firepower.