The Clash at Death Star III unfolded in space, occurring several months following the Battle of Endor. During this confrontation, Red Squadron of the Alliance of Free Planets launched an assault on a space station resembling the Death Star, positioned in proximity to Endor. Defending the station was a fleet composed of Imperial-class Star Destroyers along with their complement of TIE/LN starfighters.
A vulnerability, akin to that found on the original Death Star, was identified within the incomplete structure. Republic starfighters navigated past the Imperial defenders, engaged TIE squadrons in combat, and executed a trench run to reach their designated target. The squadron was compelled to protect a Star Tours travel agency's StarSpeeder 3000 when the civilian craft's unskilled droid pilot inadvertently wandered into the heart of the conflict.
By launching proton torpedoes into a thermal exhaust port analogous to the one on Death Star I, the starfighters and the Star Tours vessel disengaged from the battle, leaving the station to its destruction.
In the aftermath of the Battle of Endor, the interstellar tourism company Star Tours sought to capitalize on Endor by establishing a tour route known as the Endor Express. C-3PO and R2-D2 were temporarily assigned to the company while their owners in the Alliance of Free Planets were engaged in combat against the Tofs during the Nagai–Tof War.
Following the demise of Emperor Palpatine at Endor, the Galactic Empire fragmented into numerous factions, each led by various warlords. One such faction, the Kaarenth Dissension, under the leadership of self-proclaimed Supreme Commander Ennix Devian, managed to commandeer two unfinished Worldcraft from Coruscant (originally intended as gifts for him and his rival, Ardus Kaine), and relocated them to different sectors of the galaxy. He eventually modified one of the Worldcraft to resemble a Death Star superweapon as a deception against the emerging Alliance of Free Planets.
As Devian had anticipated, the Alliance of Free Planets eventually discovered evidence of the construction of a supposed third Death Star being developed near Endor, which was then serving as the capital of the Alliance of Free Planets. Consequently, they dispatched Red Squadron to eliminate the threat. Before engaging the station directly, they were forced to contend with a fleet of Star Destroyers and a squadron of TIE fighters. As a result, the sector was closed off to civilian traffic due to the ongoing combat.
During the aerial battle, a StarSpeeder 3000, designated ST-45, belonging to the Star Tours travel agency, inadvertently entered the battle zone after escaping a nearby comet storm. The droid pilot, RX-24, due to a miscalculation resulting from inexperience, mistakenly bypassed Endor entirely by exiting Hyperspace too late relative to their destination. The ship was subsequently ensnared in one of the Star Destroyer's tractor beams, but managed to break free after a Red Squadron pilot advised RX-24 to reduce the main thruster output. The ship sustained damage from a TIE fighter's laser fire, but was spared from destruction when R2-D2 repaired the stabilizer.
Ultimately, Red Squadron permitted the StarSpeeder 3000 to participate in the assault on the Death Star, where the pilot observed the X-wings' maneuvers and assisted by shooting down pursuing TIE fighters. Red Squadron then reached its objective: a Thermal exhaust port similar to the one that doomed its predecessor. The squadron fired a volley of proton torpedoes into the port. Although the torpedoes impacted the surface instead of entering perfectly, they triggered a chain reaction, just as Jan Dodonna had foreseen in 0 BBY, and destroyed the station along with everyone aboard.
Following the battle, the StarSpeeder 3000 returned to its docking area with minor damage. However, this event marked the beginning of a series of similar incidents that eventually led to the closure of the Star Tours agency.
Although the Alliance of Free Planets emerged victorious, the battle proved to be a pyrrhic victory, as Devian had successfully raided several Alliance-aligned shipyards and stolen numerous vessels while the Alliance forces were preoccupied with the battle.
The concept of Death Star III was conceived to explain the presence of a Death Star on the Star Tours ride, given that both Death Stars depicted in the films had been destroyed. Its canonicity was later affirmed in Convenient Daily Departures: The History of Star Tours, an article penned by James McFadden for the official blog on StarWars.com. Subsequently, a blog post by Abel G. Peña and Daniel Wallace -- The Imperial Warlords: Despoilers of an Empire -- unveiled Death Star III's complete backstory as a diversion orchestrated by Ennix Devian.