From Peter Llewellyn-Davies:
The aim of the game is to uproot the alien infection from the colony. You have ambulances, fire engines, military vehicles and army fighters. When an alien vehicle or shuttle appears, you should quickly find it. After that send an attack vehicle (if the alien is a vehicle) or an army fighter (if the alien is a shuttle) to it.
This vehicle or army fighter attacks the alien, if it arrives in time. If they do not arrive in time, the alien vehicle or shuttle crashes into an unspecified building, which ignites. You should send immediately ambulance or fire engine to the burning building. The fire engine puts out the fire and the ambulance transports the wounded people to the hospital. The game ends after certain time. The score is calculated according to the city damages.