The Imperial attack on and occupation of Thyferra took place during the Galactic Civil War around 1 ABY. The attack—the culmination of several weeks of planning by Moff Kohl Seerdon's to capture the Rebel Alliance's bacta supply—was crippling to the Alliance's pharmaceutical resources. Although Seerdon's military resources were greatly diminished by repeated guerrilla strikes from the elite Alliance starfighter wing Rogue Squadron, he was able to invade the planet relatively easily by manipulating the Alliance to divert their military to the Sullust system.
Rogue group was quickly dispatched to reclaim the bacta supply. A fierce battle took place, in which the Rogues succeeded in driving the Imperial forces off the planet, with some minimal civilian casualties. In a last ditch effort, Seerdon joined the battle in his custom Sentinel-class landing craft to personally confront Luke Skywalker, the Commander of Rogue Squadron. Skywalker bested Seerdon in the ensuing dogfight, effectively ending the Thyferra occupation.
The Imperial Moff Kohl Seerdon had been in the planning stages for an attack on Thyferra for some time. Intel of the Rebel Alliance quickly picked up on this, and so a string of raids on Imperial territory, spearheaded by Rogue Squadron, led by Luke Skywalker, was commenced in an effort to reduce the cunning Moff's resources.
A raid on the Imperial tibanna gas platforms on the gas giant Taloraan drastically reduced Seerdon's firepower, as tibanna was used to power blasters. Around the same time, a raid on Fest took place resulted in the destruction of Seerdon's weapons research facility and the theft of three AT-PT walkers. This operation, in particular, enraged Seerdon, who quickly responded with an attack on a Chandrilan city, home of Mon Mothma, the Chief of State of the Alliance. In retaliation for the sudden attack on Chandrila, Rogue Squadron struck at the massive Capacitor situated in a volcano on Sullust. The operation, engineered by Kasan Moor, an Imperial defector who had extensive knowledge of Imperial ground operations, was a success, and the Capacitor was destroyed.
While the Alliance forces were stationed on Sullust, Seerdon gathered whatever men and resources he had left and led his final attack on Thyferra. The Alliance's bacta supply was quickly overrun, and a massive ground force was installed in the area. General Carlist Rieekan of the Alliance notified Rogue Squadron of Seerdon's actions, and Rogue Squadron was quickly deployed to reclaim the bacta. The ensuing battle between Rebel and Imperial forces was disastrous for the Imperials: not a single walker, TIE/LN starfighter, turbolaser encampment, or stormtrooper bunker survived the battle. The Imperials experienced at least 55 casualties; in stark contrast, Rogue Squadron only lost one X-wing, and even with that the pilot, Kasan Moor, managed to survive the crash.
While defending the bacta tanks, Rogue Squadron proceeded to demolish a nearby Imperial bunker, and proceeded to retrieve seeker cluster missiles in the remains.
After the entire Imperial garrison in the area was wiped out, Moff Seerdon decided to confront Commander Skywalker personally. He arrived on the planet in his custom Sentinel-class landing craft, modified for combat purposes. Challenging Skywalker to a one on one dogfight, Seerdon battled the Rogue commander in the skies over his ruined army. As the firefight went on, Seerdon tried to convince Skywalker that he was too talented to waste his prowess with the Alliance and offered him a spot in the Imperial Navy. As it became evident that Skywalker's piloting prowess outclassed Seerdon's, Seerdon vowed that even if the Rebellion won the day, the Empire will still eventually crush the Rebellion. Shortly after, his shuttle exploded in mid air.
With the battle won, the Rebel's bacta supply was effectively secured. With only one X-wing lost during the battle, Rogue Squadron was further cemented as the Rebellion's premier task starfighter squadron.
This Star Wars: Rogue Squadron level foreshadows the Bacta War, another conflict between Rogue Squadron and wayward Imperial forces bent on controlling the galaxy's bacta supply, seen in the novel X-Wing: The Bacta War.
- Star Wars: Rogue Squadron: The Official Nintendo Player's Guide