During Nightswan's campaign, a mission to Umbara erupted into a battle 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 relayed orders to the other vessels of Admiral Carlou Gendling's task force to target Nightswan's Vulture droids while they were within the transmission shadow of the individual ships.
During the Clone Wars, the Umbarans seceded from the Galactic Republic to the Confederacy of Independent Systems after the death of Senator Mee Deechi at the hands of Lolo Purs, leading to an invasion by Clone troopers to get the planet back on the side of the Republic. 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 starships 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 to take part in 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 Vulture droids swarmed the Imperial task force. Commander Cheno ordered the Thunder Wasps gunners to intercept and destroy enemy fighters targeting the Foremostss 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 discovery. 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.
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.
The mission to Umbara first appeared in Timothy Zahn's 2017 novel Thrawn, a Canonical origins story of the titular character.
- Star Wars: Timelines