In the contested Vega Sector, Crown Prince Gilkarg nar Kiranka, Kalralahr of the Kilrathi armada was secretly overseeing the development of the Proton Accelerator Gun, also known as the Graviton Weapon. Developed on Warhammer XII, the Graviton Weapon could destroy an entire planet by increasing the gravitational force of the planet 137 times. This weapon would be used to crush the Terran colonies with ease, and the KIS Sivar would serve as the platform for this weapon.
After the loss of Venice in 2654, the Kilrathi had no choice but to abandon the Vega Sector. Gilkarg ordered the Sivar to fire on Warhammer XII to erase all evidence of the super-weapon's development, and in the test that followed, the Sivar completely destroyed the planet and all life on it. The Sivar and its task fleet then relocated to the Epsilon Sector, where they planned to destroy the Goddard Colony. The Sivar fired on the planet, killing all 250,000 Terran colonists on the planet before fleeing into deep space with its strike fleet. The Confederation sent the TCS Tiger's Claw to investigate. They found the colony world utterly devastated by the Kilrathi weapon. One pilot in particular was deeply affected by this massacre, Zachary "Jazz" Colson. He blamed the Confederation,and the Tiger's Claw in particular, for the loss of Goddard. Colson spent the next decade as a traitor to the Confederation before being killed by Christopher Blair.
In the campaign that followed, known as Operation Thor's Hammer, the Tiger's Claw pursued the Sivar and its large fleet of escorts. In several weeks of fighting, the Tiger's Claw managed to destroy the Sivar's escorts and eventually caught up with the Sivar itself in the Vigrid System. On 2655.199, after a prolonged assault by pilots Christopher Blair and Joseph Khumalo, the Sivar and its super-weapon were completely destroyed, and the Tiger's Claw thereafter retreated back to Confederation space.
The loss of the KIS Sivar and the Proton Accelerator Gun was a severe blow to the Empire's efforts to defeat the Confederation, and the technology was lost to the Kilrathi. The Confederation, however, was able to examine pieces of the wreckage including the Proton Accelerator Gun itself. The technology found its way into Confederation ships as the Phase-Transit Cannon was based in part on that found in the Sivar.