Prior to 2655, the Kilrathi controlled vast swaths of worlds spread across the Vega Sector, which was a hotly-contested territory during the Terran-Kilrathi War. Warhammer XII resided far outside the Terran Confederation's sphere of influence, thus becoming a major Kilrathi stronghold in the system. It served as the Kilrathi's main center of research and development on the frontlines, therefore it was responsible for the development and testing of a large number of Kilrathi superweapons.
It was on Warhammer XII that the Kilrathi developed the Graviton Gun, the Kilrathi superweapon that could destroy a planet by increasing its gravitational field substantially, resulting in the total loss of life and the destruction of all standing structures on the planet.
In 2655, the Vega Sector was liberated by the Terran Confederation. The Kilrathi Empire had no choice but to surrender its territories in the region, including Warhammer. Kalralahr Gilkarg nar Kiranka oversaw the final developmental stages of the Graviton Gun at this point and ordered Warhammer XII to be abandoned. He made no attempt to save the planet, and instead used it as the first test site for the Graviton Gun.
After the evacuation, the Graviton Gun was fired on Warhammer XII by the KIS Sivar, annihilating all life and structures on the surface. With the success of this test, Glikarg and his armada fled to Imperial space, where they planned the next phase of their renewed offensive on the Terrans. By the time the Terrans captured Warhammer, the Kilrathi were nowhere to be found.