According to the Office of Naval Research website, these missiles are fueled solely by electricity and do not require the use of chemical propellants.
The weapon uses magnetic fields framed by two rails to launch the projectiles.
“Using its extreme speed on impact, the kinetic energy warhead eliminates the hazards of high explosives in the ship and unexploded ordnance on the battlefield,” the Office of Naval Research explains... It cost $250 million to develop the weapon as part of the Navy’s so-called “future weapon system.”
.. eliminate the need to carry gunpowder aboard ships.
“Our need to carry gunpowder with us is a big vulnerability to our ships,” he said. “A rail gun could eliminate that need.”