Remember the video game Missile Defense? The concept was that if your enemy launches enough missiles at you, you will run out of missiles to shoot them out of the sky.
Missile Command. My favorite arcade game. I have it at home. Lapped the machine. FYI - Once you get to a million, your score goes to zero, and there is no high score recorded. Hence, once you hit I think it was around 700,000, you have to start losing on purpose to get rid of all your free cities and time it so you lose your last city as close to a 1,000,000 without going over it.