artillery. First traditional artillery uses expending air (explosion) to propel the shell. Today, that speed of air expansion has reached it limit, so the range of artillery is limited. Second, one big problem on ship is that the space is limited, to stack all those explosive, is pretty dangerous. If during a battle, the ammo cache got hit, the secondary explosion will certain create huge problem. Hence kinetic weapon that has no explosive is a big plus. Railgun is not gonna be used for anti-missile. That is the job for technology like metal storm. Kinetic weapon is used to destroy enemy ships, and bunker. During high speed impact, the kinetic energy penetrator generates extreme heat and that fragments will be ignited with air. You don't want to be even near when that thing hit.