Actually. how can a RAIL GUN shoot a straight line for one hundred miles? And hit the target dead on?
You have to account for both the curvature of the earth and the effects of gravity. It's called ballistics and the US Navy is really, really good at that. That straight line you speak, is really a very flat parabola made by gravity pulling the missile down at 32 feet per second, and the earth is really, really big. At 3960 miles, 100 miles will only get you an angle of about 0.025 radians or 1.6 degrees.