Move your cannon with the mouse, your finger, or the arrow keys, and fire with a click, tap, or space - one shot in the air at a time. Bottom rows score 10, middle rows 20, the top row 30, and the saucer across the top pays 100. Bombs chew through your bunkers and cost you a life on a hit. Clear the fleet and the next wave starts lower and faster; let them land and it is over.