Score: 0 · Wave 1 · Lives: 3 · Playing.
Arrow-Left and Arrow-Right (or A and D) to slide the cannon — it never moves up or down. Space to fire, and only ONE shot at a time, so wait for it to land. The formation steps sideways, drops a row and turns round at the walls, and gets faster as you thin it out. The four bunkers block shots from either side and wear away. Clear every invader to advance a wave.