Battle over Umbara Before 2 BBY , a battle erupted above the planet Umbara between the naval forces of the Galactic Empire and forces controlled by the mysterious individual known as Nightswan . The battle ended in the Empire ' s favor when Captain Thrawn convinced Commander Alfren Cheno and the other Imperial officers to countermand Admiral Carlou Gendling ' s orders and bombard the transmitter controlling Nightswan ' s Vulture droids . Prelude . During the Clone Wars , the Umbarans had switched sides from the Galactic Republic to the Confederacy of Independent Systems , leading to an invasion by Clone trooper s . By the Imperial Era , the planet Umbara had become a major producer and exporter of doonium . Doonium was a metal used in the construction of starship s with vast quantities of it being requisitioned for the Imperial Navy ' s fleet and the secret Death Star project . The pirate – turned – insurgent leader Nevil Cygni , who was known as " Nightswan " , engaged in smuggling doonium , tibanna , and iridium in order to raise funds for his insurgency against the Galactic Empire . After finding it difficult to bribe the Umbaran authorities , Nightswan decided to instigate an uprising on Umbara in order to facilitate the Imperial takeover of the planet ' s mining and refining sector . Nightswan reasoned that it would be easier to bribe the Empire than the Umbaran authorities . As part of the uprising , Nightswan ' s operatives installed a ground - based transmitter on Umbara ' s outermost moon . Using his underworld contacts , Nightswan also obtained 400 former Separatist Vulture droids as part of the uprising . An Imperial task force led by Admiral Carlou Gendling was dispatched to suppress the uprising . Gendling ' s forces included the Imperial Star Destroyer " Foremost " , two " Raider " - class corvettes , and the Imperial light cruiser " Thunder Wasp " , which was commanded by Commander Alfren Cheno . One of Cheno ' s subordinates was the Chiss Captain Thrawn , who had joined the Imperial Navy in order to cultivate an ally for the Chiss Ascendancy . Admiral Gendling hoped to use military force to intimidate the Umbarans but was instead met by Vulture droids . The battle . The Vulture droids swarmed the Imperial task force . Commander Cheno ordered the " Thunder Wasp " gunners to intercept and destroy enemy fighters targeting the " Foremosts " dorsal surfaces . Thrawn ' s friend Ensign Eli Vanto analyzed the attack patterns and traced the Vulture droids back to Umbara ' s outermost moon . Thrawn deduced that the Vulture droids had not been sent by the Umbarans , who were waiting to engage the Imperial forces in a weakened position . With the " Thunder Wasp " and other ships overwhelmed by the nimble Vulture droids , Thrawn and Vanto , with the approval of Commander Cheno , took control of the chief sensor officer ' s Hammerly ' s station . After scrutinizing the Vulture droid ' s attack patterns , Thrawn and Vanto deduced that the Vulture droids were being controlled by a transmitter on Umbara ' s outer moon . Having isolated the location of the ground - based transmitter , Thrawn convinced Commander Cheno to inform Admiral Gendling of their discover . However , Admiral Gendling was unwilling to take risks and ignored Commander Cheno and Thrawn . Thrawn then ordered the comm officer to contact all ships and tell them to target the transmission shadows where the vulture droids relied on their own programming . This tactic destroyed all the Vulture droids , turning the tide of the battle in favor of the Empire . Aftermath . Following the destruction of the vulture droids , the Umbarans surrendered unconditionally . The " Foremost " dispatched stormtrooper squads to supervise the surrender of the insurgents . The Imperials lost one " Raider " - class corvette while the other ships including the " Thunder Wasp " and " Foremost " sustained considerable damage . Despite the Imperial victory , Admiral Gendling was furious that Commander Cheno had apparently usurped his authority . Before Gendling could question Thrawn , Commander Cheno took the fall to protect Thrawn . While Thrawn did not want Cheno to protect him , Cheno told Thrawn that he saw potential in him and added he was willing to sacrifice his own career to protect his crew . Following the battle , Vanto investigated the ground transmitter station on Umbara ' s outermost moon and found that the station had been operated by humans . Vanto discussed his findings with Thrawn and the two concluded that Nightswan had instigated the Umbaran uprising in order to facilitate the Imperial takeover of Umbara ' s mining industry . Eli surmised that Nightswan believed it would be easier to bribe the Imperial inspectors than the Umbarans . Thrawn believed that the Umbara incident was a step in Nightswan ' s campaign against the Empire . Behind the scenes . The Battle over Umbara first appeared in Timothy Zahn ' s 2017 novel " Thrawn " , a Canon ical origins story of the titular character .