This fairly addictive game involves the defence by you of the "five most important cities on the planet Earth" against up to four bombs dropped by an unsporting enemy alien. The cities in question are New York, Lubbock, Chicago, Washington and Los Angeles.
There are four levels of play, relating to speed of descent, although you can select from nine.
The controls of your defending ship, operated from the keyboard, only become active after the last bomb is released, so at higher skill levels there can be quite a sense of urgency about the game.
You can fire in only one direction but your ship can rotate through 360 degrees in 45 degree steps and can move in the direction it fires.
This control can lead to some quite effective displays as you swoop down on an alien or a bomb, gun blazing.