An unfortunate combination of paper and ink makes reading what's on the screen rather difficult. However, by studying the inlay, you can determine what is supposed to be happening. You have a choice of keyboard, or joystick, individual or team play.
The object is to destroy waves of aliens by manipulating two cannons. One lies at the bottom of the screen, and the other at the right. By using a combination of keys, the cannon can be made to fire diagonally, as well as right angles. The diagonal cross fire could destroy your own cannon, of course, so careful positioning is needed. If any aliens do manage to land on your plane they will march towards you and can only be destroyed by an electro bolt. You start with three of these bolts, and can collect up to four more. Later assault waves bring "pods", which you cannot destroy. They have a disturbing habit of suddenly exploding, and will destroy your cannons if they are in the path of any fragments.
I found the combination of keys tiring, and got the impression that the action didn't match my efforts on the keyboard. Altogether a disappointing experience.