Railgun is something we know from video games. Railgun was dreamed as a gun that can fire the bullet at much higher speed than a normal gun. U.S. Navy has actually turned that into reality.
They have made and tested a giant railgun capable of thwarting a bullet/slug at mach 7, i.e. 7 times the speed of sound in air.
The railgun surely creates a powerful sonic boom. With this speed, the gun gives the side strategic advantage in almost any land war and even in air or sea war.