Battle over Umbara

During the era of the Clone Wars, the Umbarans, inhabitants of the planet Umbara, chose to leave the Galactic Republic and align themselves with the Confederacy of Independent Systems. This decision followed the death of Senator Mee Deechi at the hands of Lolo Purs, which prompted an invasion by clone troopers aimed at restoring the planet to the Republic's control. Despite a period of resistance during the early years of the Imperial Era, Umbara eventually became integrated into the Galactic Empire, though it maintained a certain degree of self-governance. The planet subsequently found itself heavily indebted to the Empire.

Umbara served as a major source and exporter of doonium, a metal vital for the construction of starships. Massive quantities of this resource were allocated to the Imperial Navy's fleet and the clandestine Death Star project. Nevil Cygni, a former pirate who had transitioned into an insurgent leader and was known as "Nightswan," was involved in the illicit trafficking of doonium, tibanna, and iridium. These activities were intended to generate funds for his insurgency against the Galactic Empire.

After determining that bribing the Umbaran authorities was proving difficult, Nightswan resolved to incite an insurrection on Umbara. His objective was to pave the way for the Empire to seize control of the planet's mining and refining operations, believing that the Empire would be easier to corrupt than the local government. As part of his plan, Nightswan's agents installed a transmitter on the surface of Umbara's outermost moon. Furthermore, through his connections within the underworld, Nightswan acquired 400 decommissioned Separatist vulture droids to participate in the planned revolt.

An Imperial task force, under the command of Admiral Carlou Gendling, was deployed to quell the unrest. Gendling's fleet included the Imperial Star Destroyer Foremost, a pair of Raider-class corvettes, and the Imperial light cruiser Thunder Wasp, which was under the command of Commander Alfren Cheno. Serving under Cheno was the Chiss officer Captain Thrawn, who had enlisted in the Imperial Navy with the intention of forging an alliance for the benefit of the Chiss Ascendancy. Admiral Gendling initially hoped to use the presence of his forces to intimidate the Umbarans into submission, but his fleet was instead met with an assault by the vulture droids.

The Imperial task force found itself under attack from swarms of Vulture droids. Commander Cheno instructed the gunners aboard the Thunder Wasp to prioritize intercepting and destroying any enemy fighters targeting the dorsal sections of the Foremost. Ensign Eli Vanto, a friend of Thrawn, analyzed the patterns of the attacking droids and traced their origin back to Umbara's outermost moon. Thrawn concluded that the Umbarans themselves were not behind the attack, as they were likely waiting for the Imperial forces to be weakened before engaging them. As the Thunder Wasp and other vessels struggled against the agile Vulture droids, Thrawn and Vanto, with Commander Cheno's approval, assumed control of the sensor station operated by the chief sensor officer, Hammerly.

After carefully examining the attack patterns of the Vulture droids, Thrawn and Vanto determined that they were being remotely controlled by a transmitter located on Umbara's outer moon. Having pinpointed the location of this ground-based transmitter, Thrawn persuaded Commander Cheno to inform Admiral Gendling of their discovery. However, Gendling, unwilling to take any risks, dismissed the information provided by Cheno and Thrawn. Thrawn then bypassed Gendling's authority and ordered the comm officer to contact all ships, instructing them to target the transmission shadows where the vulture droids were forced to rely on their autonomous programming. This strategy proved highly effective, leading to the destruction of all the Vulture droids and shifting the momentum of the battle in favor of the Empire.

With the Vulture droids eliminated, the Umbarans offered their unconditional surrender. The Foremost deployed squads of stormtroopers to oversee the surrender of the insurgents. The Imperials suffered the loss of one Raider-class corvette, while the remaining vessels, including the Thunder Wasp and Foremost, sustained significant damage. Despite the Imperial victory, Admiral Gendling was enraged that Commander Cheno had seemingly undermined his authority. Before Gendling could confront Thrawn, Cheno took responsibility for the unauthorized actions in order to protect Thrawn from repercussions.

Although Thrawn did not want Cheno to shield him, Cheno explained that he recognized Thrawn's potential and was willing to sacrifice his own career to safeguard his crew. Following the battle, Vanto investigated the ground transmitter station on Umbara's outermost moon and discovered that it had been operated by humans. Vanto shared his findings with Thrawn, and together they concluded that Nightswan had orchestrated the Umbaran uprising as a means to facilitate the Imperial takeover of Umbara's mining industry. Eli theorized that Nightswan believed it would be easier to bribe the Imperial inspectors than the Umbaran authorities. Thrawn assessed that the Umbara incident was a component of Nightswan's campaign against the Empire.

As a result of the unconditional surrender and the Empire's victory in the engagement, the Umbaran people ultimately responded to the battle by completely ceding control of their homeworld to the Imperial regime, thereby relinquishing the last vestiges of their independence. By surrendering Umbara, the Umbarans also succeeded in settling their debt to the Empire; however, in reality, there was no viable means for the Umbarans to resolve that debt without surrendering the remainder of their autonomy. Consequently, Umbara came under the direct governance of the Empire.

The battle over Umbara was first depicted in Timothy Zahn's 2017 novel, Thrawn, which serves as a Canonical origin story for the character of the same name. The notion that Umbara had enjoyed a degree of independence under the Empire, which it was subsequently compelled to relinquish, was mentioned in the later 2017 novel Leia, Princess of Alderaan. However, the connection between that surrender and the battle portrayed in Thrawn was not established until the publication of the 2019 reference book Ultimate Star Wars, New Edition.