The Battle of Sullust unfolded in 4 ABY during the Galactic Civil War. It pitted the forces of the Alliance to Restore the Republic against those of the Galactic Empire. The purpose of this conflict was to draw the Imperial Navy away from the forest moon of Endor, setting the stage for the impending Battle of Endor. As the Rebel fleet gathered within the Sullust system and clashed with Imperial warships, Renegade Squadron launched a ground assault. Despite the ground battle ultimately revealing itself as a trap orchestrated by the local Imperial commander, the squadron maintained their position until the planet's liberation. Contrary to the Alliance's expectations, Emperor Palpatine recognized their ruse and refrained from dispatching the Imperial Navy to Sullust.
The Alliance to Restore the Republic intended to utilize the same hyperlane as the Imperials to arrive at Endor, the location of the still-under-construction second Death Star. By this point, the Sullustans had successfully overthrown the pro-Imperial SoroSuub Corporation's control over Sullust, establishing a democratic government. While the planet couldn't openly join the Rebel Alliance, the new government permitted the Alliance Fleet to assemble within the system. A Rebel fleet congregated in the Sullust system, marking the beginning of their route. The Rebel forces then initiated an attack on the planet with the aim of deceiving the Empire. Their goal was to make the Emperor believe that Sullust itself was the Rebels' primary target, rather than the Death Star. As the Rebels continued to consolidate their forces at the system's designated rallying point, they deployed fighters to protect the arriving capital ships. The cruisers Defiance and Independence were expected to arrive shortly. With the Imperial fleet closing in, the threat to the cruisers was significant. The Defiance group had already participated in minor engagements and anticipated further attacks on their way to Sullust. The Independence had also encountered Imperial patrols and expected a larger force to intervene. It was crucial for these cruisers to reach the rendezvous point at Sullust to ensure that, under Admiral Ackbar's command, the attack on Endor would not be a futile endeavor.
To bait Imperial forces, Commander Col Serra's unit, Renegade Squadron, was tasked with capturing the Imperial Garrison stationed on the planet. Before this battle, the unit had launched an attack on Korriban, where Emperor Palpatine was undertaking a Sith pilgrimage. The Emperor's shuttle held sensitive data regarding his schedule, and while he was trapped within a Sith tomb by the unit, a soldier managed to steal a databank from the shuttle. This databank was later used to confirm that the Emperor would be aboard the Death Star II during the Alliance's assault.
Leaving the Mon Calamari Cruiser Liberty, Ace Azzameen departed for the Defiance group. Upon his arrival, two Carrack-class cruisers and a Victory-class star destroyer appeared, deploying TIE/LN starfighters and TIE/sa bombers.
Eventually, the Defiance task force jumped into hyperspace and joined the Liberty. Ace followed suit and headed towards the Independence. Upon arriving in-system, Ace discovered the Imperial II-class Star Destroyer Immortal had commenced its attack, prompting Ackbar to deploy B-wings from Green Group. Once again, Ace was tasked with protecting and escorting the fleet. Ace successfully repelled the attackers, allowing the Independence to escape into hyperspace, with Ace following moments later.
After landing on the planet, Renegade Squadron swiftly assaulted the Imperial outpost, which was suspiciously lightly defended. Concerned, Col Serra contacted Alliance command to inform them that the unit might have stumbled into a trap. His suspicions proved correct when an unidentified IG-88 unit emerged and ambushed them. This unit was equipped with a shield, rendering it impervious to blaster fire. Serra interpreted this as a form of retribution for Renegade Squadron's humiliation of Darth Vader during the Battle of Hoth. Nevertheless, the unit quickly identified the source of the shield as a lightning conduit, which they promptly destroyed. With the droid now vulnerable, the unit forced it to retreat, but not before it inflicted significant damage.
Following IG-88's retreat and the rebel fleet's jump into hyperspace towards Endor, leaving behind two MC80 Star Cruisers, a series of gravity well projectors were activated, preventing Renegade Squadron's escape. To disable the gravity wells, the shield generator needed to be deactivated first. The Imperial officer in possession of the necessary codes was assassinated, and his codes were retrieved by a Renegade Squadron soldier and uploaded into the shield mainframe. Now vulnerable, the gravity well projectors were destroyed. The unit continued to fend off Imperial reinforcements until Sullust was liberated, after which they were compelled to withdraw due to the imminent Battle of Endor, where their presence was required.
Darth Vader was informed about the Rebel presence in the Sullust system and relayed this information to Emperor Palpatine, who dismissed it, focusing instead on his own plan to annihilate the Rebel fleet over Endor. Realizing their deception had failed, Renegade Squadron proceeded to Endor to assist General Han Solo in battle. The liberation of Sullust marked the unit's penultimate engagement before its disbandment.
Following the Rebel victory at Endor and the Emperor's demise, Sullust became one of the first worlds to formally join the Alliance of Free Planets, and subsequently the New Republic.
"Reports of a Rebel fleet massing near Sullust" were initially mentioned by Darth Vader in Star Wars: Episode VI Return of the Jedi. The gathering and the ensuing space battle were depicted in Star Wars: X-Wing Alliance. The Expanded Universe provided no further details about this event until the release of Star Wars Battlefront: Renegade Squadron in 2007, which detailed the ground battle. The Essential Atlas later retconed that Renegade Squadron's mission was merely a minor raid intended to draw Imperial forces and justify the Rebel fleet's presence in the system.