Inside a metal shell being hurled from a standstill to a speed many times faster than sound, the pressure could be as high as an elephant standing on every square inch of a human body. To make matters worse, an invisible, violent magnetic storm is raging through its path. This is the world inside an electromagnetic rail gun. For decades, this has been the nightmare that kept weapons engineers awake. Their dream was to place a guidance chip inside a rail gun shell so it could steer itself to a...