The mass driver is a large weapon for a warship's hardpoints, built in an Armory. It throws slugs at long range only. A slug takes time to arrive: a fast target that sees it coming evades part of the damage, and a target that leaves, is disabled or pulls back out of range before it lands is missed entirely.
It cannot aim at anything smaller than a corvette, and its weight lowers the speed of the ship that carries it.