A Gravitic Drive was a device similar to a Dovin basal that propelled a ship by manipulating gravimetric fields. Gravimetric drives benefit from greater acceleration, deceleration and maneuvering capabilities. Because of the lessened effect of inertia upon ships with this technology the vessel can move from a complete stop to full throttle with ease. The same kind of acceleration would crush crew and likely the ship itself on any vessel without gravimetric fields.
Adapting a Gravitic Drive to defensive roles is much easier than offensive. In addition to the benefits that gravimetric fields lend to propulsion and artificial gravity, the same fields can be used to deflect incoming fire away from the ship's hull. By encapsulating the entire ship in a close, negative G-Force field any incoming missiles, lasers, etc. would either be completely deflected or partially deflected. This kind of technology would require the ability to manipulate gravimetric fields to within meters of any capital ship's hull. Keeping the "Gravimetric Shields" active would also require a large power source. Such shielding may only be activated during battles, when incoming fire is detected or it may receive power boosts when incoming fire is expected. As such, use of the "Gravimetric Shield" was limited only to combat or when moving through areas of dense particles, like Asteroid Belts.