The confrontation known as the Battle of Derra IV involved forces of the Galactic Empire clashing with a Rebel Alliance transport group in the vicinity of the planet called Derra IV.
While Grand Admiral Thrawn was engaged in diminishing the power of the criminal syndicate Black Sun on Corellia, he learned that the Hopskip, a freighter involved in illegal weapon shipments, was headed towards Derra IV. This intelligence, coupled with other data gathered by Imperial Intelligence, revealed the intention of a Rebel supply convoy to depart from that planet towards a newly established Rebel base. Darth Vader and Thrawn collaborated in devising a strategy to deploy the 181st Imperial Fighter Group to neutralize the Rebel forces.
Vader unveiled this strategy to the pilots, with Soontir Fel discerning that the plan originated from the quiet alien Admiral. This realization provoked Fel, who felt disdain for the contradiction of an alien being relied upon to save the Empire while Human superiority was a primary justification for Imperial policies. Ironically, Thrawn would not be acknowledged for his contribution to the battle, and Fel would later serve under another Chiss officer within the Empire of the Hand.
The convoy departed Derra IV, but before achieving hyperspace jump, an Star Destroyer materialized, unleashing the TIE fighters of the 181st upon the unsuspecting Rebel vessels. Despite Renegade Flight's valiant efforts to protect the convoy, it faced total destruction. Subsequently, Renegade Flight, a component of Red Squadron, was also annihilated, with Commander Narra meeting his demise at the hands of Fel.
Despite its relatively small scale and uneven nature, the battle represented a significant triumph for the Empire. The three leading figures of the 181st (Turr Phennir, Evir Derricote, and Soontir Fel) received promotions during a grand ceremony on Coruscant, presided over by Emperor Palpatine. Phennir assumed command of the 181st's second squadron, earning a promotion to Commander for destroying four Rebel transports. Derricote was appointed to oversee the Imperial facility on Borleias, achieving the rank of General. Fel was promoted to Colonel, given command of the 181st, and was granted the Fel estate on his home world of Corellia as a Baron of the Empire, where he relocated his family soon after. Although Thrawn conceived the plan, he received no recognition for the battle's success. Given his existing rank of Grand Admiral, it's possible there were no further honors to bestow. Some have speculated that Ysanne Isard influenced the Emperor to reassign Thrawn to the Unknown Regions to avoid the embarrassment of an alien's strategic brilliance.
Furthermore, the battle left the Rebel defenses at Echo Base on Hoth severely understaffed, without opportunities for resupply, and reliant solely on Rogue Flight for defense. Following Commander Narra's death, Luke Skywalker of Rogue Flight was promoted to Commander and assumed leadership of Red Squadron, which he subsequently transformed into Rogue Squadron.
This battle was later adapted into a simulation for New Republic pilots to practice. While held captive on Coruscant in 40 ABY, Wedge Antilles attempted the simulation without success.