The Navy’s Rail Gun technology hides a secret, that the Navy’s projectile accuracy has been substantially increased by about 45x.
But first some history.

The US government brought Prof Eric Laithwaite to help them build a rocket launcher based on linear motor principles. Today we call this the Rail Gun. In terms of its original objectives it was not a success, because astronauts could not survive the accelerations required to launch from a rail gun and cargo required a much longer rail gun than feasible with the then technologies.

The Navy succeeded with ship based rail guns as a means to shoot projectiles. Bloomberg TV has a good video on the Navy’s Rail Gun. http://www.bloomberg.com/video/watch-navy-s-new-supergun-launch-shells-at-5600-mph-bfCXOGXZQziZgHnsbq9VzQ.html