Destruction of Byss

During the course of the Battle of Onderon, a special forces team, under the leadership of Lando Calrissian together with Kam Solusar, boarded Palpatine's flagship, the Eclipse II, by physically attaching the freighter Millennium Falcon onto the underside of the Star Dreadnought.

The astromech droid R2-D2 then proceeded to sabotage the ship's automated hyperdrive system, reprogramming it to set a direct course for Byss, specifically targeting the location of the infamous Galaxy Gun superweapon. Despite the crew of the Eclipse II's desperate attempts to regain control, the Star Dreadnought jumped into hyperspace.

The entire sequence unfolded so rapidly that the crew of the Millennium Falcon were unable to detach their ship prior to the jump, resulting in their forced participation in a voyage to the Deep Core alongside the warship.

As the events on Onderon were playing out and the Eclipse II transmitted a distress signal requesting reinforcements, the Galaxy Gun's chief engineer, Umak Leth, made the risky decision to arm the weapon in an effort to aid his Emperor and reclaim some of the prestige he had lost after the Nespis VIII fiasco.

Just as the Galaxy Gun was nearing operational readiness, the Eclipse II abruptly emerged from hyperspace, directly colliding with the massive cannon and inflicting significant damage to both vessels. The Millennium Falcon successfully disconnected from the Star Dreadnought just before the impact and prepared to jump to hyperspace. As the Eclipse II struck the Galaxy Gun, the cannon, in a last-ditch effort, launched its armed missile toward the ship that was on a collision course.

The missile was ensnared by Byss's gravitational field, detonated upon impact with the planet's surface, and obliterated the world. This cataclysm also destroyed a portion of the orbiting fleet (which had been significantly thinned out, with ships deployed elsewhere in the galaxy), along with the wreckage of both the Galaxy Gun and the Eclipse II. The Falcon managed to escape the Beshqek system before being struck by debris from the explosion.

Following the destruction of Byss and the loss of two major superweapons, Imperial Captain Sergus Lanox later reflected on the event. He stated that upon receiving news of the disaster, he felt, deep down, that it signaled the definitive end of the Dark Empire. He also noted the devastating impact the news had on other former Imperial officers.