The battle began when T-65 X-wing starfighters of Rogue Squadron and B-wing starfighters of Green Squadron dropped out of hyperspace and began to systematically destroy KDY-77's stationary defenses. Avenger Squadron, assigned to defend the interdictor cruiser Compellor while undergoing refits, was caught off-guard in the repair yard's hangar bay and wound up heavily damaged by Rogue Squadron. Following the destruction of the turbolaser emplacements, Captain Rigell of the Compellor realized the goal of the Rebel strike team was to capture the interdictor itself. In order to avoid the Rebel capture of his command, Rigell ordered the Compellor disengaged from spacedock and headed for the safety of hyperspace. Green Squadron, however, disabled the escaping interdictor, paving the way for the assault transport Lomavcek to board and capture the Compellor.
At this point both the Victory-class Star Destroyer Inexorable and the Strike-class medium cruiser Ironhand reverted to realspace near the site of the battle, forming a two-pronged strike force. Further complicating matters for the Rebel strike team was the appearance of Assault Gunboats whose primary goal was the destruction of the Lomavcek. Both Inexorable and Ironhand deployed TIE/IN interceptors in order to bind the Rebel squadrons present. Soon though, the Lomavcek reported the capture of the interdictor to be complete. Acting under orders to prevent this technology from falling into Alliance hands, Inexorable launched a full squadron of stormtrooper transports loaded with proton torpedoes, intent on destroying the Compellor. Rogue Squadron effectively prevented this by intercepting already-launched warheads and destroying the transports. After finishing off the transports the Rebel fighters attacked the Ironhand. They managed to destroy it just after the Compellor entered hyperspace. Then, with the Compellor safely in hyperspace on its way to Mobetta, the remaining Rebel forces headed into retreat.
While the ambush in the Goff system already saw the Alliance taking the initiative in the campaign against Task Force Vengeance, the Battle of Swellen was a turning point. With the capture of the Imperial interdictor Compellor, the Imperial task force had lost its ability to drag ships out of hyperspace at will. Knowing this, Task Force Vengeance would mount a unprecedented search effort for the Compellor in order to recapture or destroy the valuable cruiser.