Protect your six cities from the incoming enemy ICBMs. Touch the
screen to fire your lasers, but don't waste shots, because each laser tower
only has 50 shots.
Enemy planes and satellites will fly overhead, destroy them before they get
chance to fire at you.
Enemy bombs require a direct hit to be destroyed.
At the end of each attack wave, you get a bonus depending upon the number
of remaining cities and shots.
You get a bonus city for every 10000 points.
The game ends when all six cities are destroyed.