We have seen mass drivers in action when the Centarai bombed the Narn Homeworld. We have been told that these weapons are extrememly effective, but banned and abhorred by all the races in B5. The fact that the Centarai used them was a shocking breach of intergalactic law. However, if this weapon was super effective in starship combat, would truely desperate races facing extinction really refrain from using it, like Earth in the Earth-Minbarai war and the Narn before being concoured? Even truly evil races with no regard for intergalactic law like the Drak (who are prefectly willing to use planetkillers and shadowtech diseases) have not been seen to use mass drivers.

The only logical explanation is that while massdrivers are tremendously effective at attacking targets on planets, they are ineffective at attacking ships. This makes sense because what causes the asteroid to do terrible damage is the kinetic energy it picks up falling down the planet's gravity well. Furthermore, interceptors have a reasonable chance of deflecting a plasma burst or a missle attack, and an asteroid is much slower, larger and easier to target. With that in mind, here are the rules:

A Mass driver attack has a base range of 6 MU. At this range, if the target ship has an interceptor or anti-fighter weapon covering that arc, the mass driver's attack will probably be deflected. Anti-fighter weapons treat each incoming asteroid as a single attacking fighter. The anti-fighter weapon attacks the asteroids normally, and if other fighters are in range, any leftover 'hits' can be applied to the fighter group. Interceptors in 'anti-pulse' instead of 'anti-fighter' mode automatically deflect any number of asteroids fired at that ship. Fighter screens can also defend against incoming asteroids, attacking them once as if they were a 'raider' fighter. If the asteroid is still undestroyed, it hits the ship and does 10 points of damage (or possibly more, for super heavy mass drivers). If the target ship is greater than 6 MU away, the asteroid takes more than one turn to reach the target. Each turn the asteroid travels 6 MU + the velocity of the firing ship at the time of firing. If the target ship makes any acceleration or applies any thruster push, the asteroid misses. This is only useful against disabled ships, space stations or bases.

When fired against a planet however, the results are much different. It is impossible to deflect the asteroid from interceptor fire from the ground, gravity will cause the asteroid to fall regardless and even if blown in pieces, all the pieces will strike the ground with only slightly changed kinetic energy. Mass drivers fire large enough asteroids that they survive re-entry with little loss of destructive power. Asteroid strikes cause destruction equivalent to powerful nuclear explosions, and are even more widely destructive if directed against planetary oceans, causing tidal waves. In a campaign game, if a fleet with mass drivers occupies a system, they can effectively destroy any colony they know about. Because of the size of the asteroids used, only a few can be carried at a time and it is necissary to rearm, but this can easily be done from any astroid or moon in the system. Because of this however, it can take a while for a fleet to fully destroy a colony and a defending fleet can sometimes make a heroic rescue.

Less advanced spacefaring races who have not developed starfighter and interceptor technologies might use mass drivers

to Rules page.