During the Thrawn campaign in 9 ABY, the brief Battle at Ukio transpired. In this engagement, Grand Admiral Thrawn of the Imperial forces successfully deceived Ukio into surrendering. This was achieved by utilizing cloaked cruisers to launch a bombardment from beneath the protection of the planetary shield, synchronized with an orbital assault carried out by the Imperial fleet positioned in orbit.
Ukio held significance as one of the five primary sources of agricultural resources for the New Republic, governed by the Ukian Overliege. Prior to the commencement of Thrawn's campaign, the Empire had relinquished its dominion over Ukio.
In preparation for his offensive on Ukio, the Grand Admiral strategically deployed elements of his fleet, including Imperial-class Star Destroyers such as the Bellicose, Judicator, Nemesis, and Death's Head, to execute diversionary maneuvers targeting Ando Prime, Filve, Crondre, and Ord Pardron. This tactic aimed to divert the already strained forces of the New Republic, which had previously suffered setbacks during the battle for the recovery of the lost Katana fleet. For the actual assault, Thrawn committed two Star Destroyers, including his flagship, the Chimaera, alongside ten Katana Dreadnaughts, and an unspecified quantity of cloaked cruisers. The Dark Jedi Joruus C'baoth was present to oversee and harmonize the orbital bombardment delivered by the cruisers through the application of battle meditation.
As the Chimaera, accompanied by its Dreadnaught escort, approached Ukio's surface in a high orbit above the sunlit side of the equator, Thrawn issued a demand to the Ukian Overliege, insisting on their submission to the Empire. He ordered them to deactivate their planetary shield and confine their military forces to their respective bases, awaiting Imperial occupation. In response to the Ukians' hesitation, Thrawn initiated a retaliatory action, instructing the Chimaera to discharge its turbolaser batteries against the planetary shield. Predictably, the shield successfully deflected the incoming blasts. However, under the influence of C'baoth's mind control abilities, the two cloaked cruisers, positioned just beneath the shield at the precise points of impact from the Chimaera's fire, retaliated by targeting the planetary surface. This resulted in the complete destruction of two Ukian military air bases. The near-simultaneous timing of these events, coupled with the extensive damage inflicted on the surface, led the Ukians to believe that Thrawn had developed a superweapon capable of penetrating planetary shields, conveniently sized to fit aboard a Star Destroyer.
Rather than face further devastation, the Ukian Overliege chose to surrender to Thrawn, accepting his stipulated terms. These conditions included the deactivation of Ukio's planetary shield and granting Imperial occupation forces control over the shield generators and all ground-to-space artillery systems. Furthermore, all military vehicles exceeding the size of a command speeder were to be seized by the Imperial occupiers. In exchange for accepting an Imperial military presence, Thrawn pledged not to interfere in the local political and social governance of Ukio and to exempt the planet from wartime taxation and military conscription. Nevertheless, Thrawn also mandated that a substantial portion of Ukio's food production and processing capabilities be redirected to support the Imperial war effort. Rumors quickly spread throughout the galaxy regarding the Empire's alleged development of a superweapon capable of breaching planetary defense shields. However, the New Republic, after analyzing a macrobinocular recording of the attack captured by Samuel Gillespee and subsequently forwarded to them by Talon Karrde, later refuted this claim.