Missiles move at a fixed vertical rate. A missile going straight down and one traversing the whole screen horizontally will take the same amount of time to hit you.
You can have as many defensive missiles in flight as you have cities remaining.
The rate at which attacking missiles spawn slowly increases.
There are no levels. There are no bonus cities to make up for casualties. There is no way to win. I may fix this later ;-)
"p" pauses
You may need SeaMonkey 1.0.1 or Firefox 1.5.0.2 or newer if you are seeing blue cities rather than red-brown cities