The coup forces under Demetrius Zaarin, a former Grand Admiral, were established with the goal of overthrowing Emperor Palpatine and seizing control of the Galactic Empire. Despite being favored by the Emperor, Zaarin grew dissatisfied with Palpatine's leadership and resolved to claim the throne for himself. He successfully recruited Arden Lyn, a disillusioned Dark Jedi, to his cause. An attempt to enlist the skilled TIE pilot Maarek Stele proved unsuccessful. The initial action of his forces involved an assault on Coruscant targeting Palpatine's flagship, the Majestic. However, the attack was repelled by Darth Vader, Stele, and a group of pilots who defended the Emperor and defeated Zaarin's initial assault. Subsequently, Zaarin's regime retreated to the Outer Rim Territories, where they waged a campaign against the Empire until Zaarin's death shortly before the Battle of Endor, in 3 ABY.
In the year 3 ABY, Grand Admiral Demetrius Zaarin, while ostensibly pursuing the renegade Admiral Harkov, began formulating his scheme to depose Emperor Palpatine and usurp leadership of the Galactic Empire. As Imperial forces were engaged in suppressing Harkov's pro-Rebel Alliance activities, Zaarin secretly amassed a personal army to facilitate his imperial takeover. Leveraging his extensive resources and cutting-edge technologies, Zaarin aimed to swiftly and decisively overthrow the Emperor.
Later, Darth Vader captured and executed Admiral Harkov for treason. Imperial loyalists then tracked Harkov's surviving fleet to the Ottega system, where they had allied with Rebel forces. Overwhelmed, the Imperials requested assistance from Zaarin and his forces to eliminate Harkov's fleet. It was at this point that Zaarin initiated his coup d'état. Upon arriving at the scene, Zaarin's forces, instead of aiding the Imperials, turned on the Imperial Star Destroyer Garrett, Vader's flagship. Although the loyalist forces managed to repel Zaarin's attack and eliminate Harkov's allies, the Galactic Empire was weakened. Consequently, Imperial forces loyal to the Emperor rushed to Coruscant to quell the impending coup.
Zaarin subsequently seized and boarded the Emperor's personal flagship, the Majestic. With Palpatine in custody, Zaarin ordered his strike team to deliver the Emperor to him personally on his flagship, Glory. However, loyal Imperial forces, led by Darth Vader and Vice Admiral Thrawn, intervened and rescued the Emperor. With the coup thwarted, Zaarin and his task force fled to the Outer Rim Territories.
Despite the failure to depose Emperor Palpatine, Zaarin remained active, leading a splinter government. Operating from the Glory and his remaining bases, his insurrectionist forces launched a campaign of terror and sabotage against the Empire. Zaarin's initial strategy involved depriving the Empire of his advanced technologies to maintain a technological advantage. He began by destroying the TIE/Advanced starfighter Deep Space Manufacturing Facilities of Omar. Despite suffering significant losses, Zaarin successfully destroyed all TIE/Advanced facilities in the Omar system, inflicting a major blow on the Empire. Zaarin continued his campaign by attacking the Imperial space station Research, a facility previously under his command. By destroying the facility, Zaarin aimed to prevent the Empire from accessing the newly-commissioned TIE/D Defender, which was still under development. Once again, Zaarin achieved victory by destroying Research, but the surviving TIE Defender prototypes were safely transferred to Coruscant before the base's destruction.
This setback did not halt Zaarin's war of attrition against the Empire, as he continued to raid Imperial facilities for valuable technologies. In the battle for control of the TIE Defender technology, Zaarin collaborated with various pirate groups in the Outer Rim Territories to secure the resources and personnel needed for the development and manufacture of the TIE Defender. This resulted in the acquisition of the fighter craft by the Nami, a warrior race aligned with the Rebel Alliance. However, loyal Imperial forces resolved this crisis before the technology fell into Rebel hands, ensuring Zaarin maintained his technological advantage.
The growing threat posed by Admiral Zaarin led Emperor Palpatine to promote Vice Admiral Thrawn to the rank of Grand Admiral, filling the vacancy left by Zaarin. The Emperor tasked Thrawn with destroying Zaarin and his treacherous fleet. Thrawn's strategy involved denying Zaarin his technological advantage through the top-secret development of a heavy starfighter capable of countering the TIE Defenders. This starfighter, the Missile Boat, would lead Thrawn's campaign to destroy Zaarin's armada.
Admirals Zaarin and Thrawn clashed in the Semag system in the Unknown Regions, where Thrawn aimed to cripple Zaarin's starfleet before another attempt on the Emperor's life could be staged. Thrawn's campaign proved devastating, eliminating many forces loyal to Zaarin, but both sides suffered heavy losses. To lure Zaarin out, Thrawn set traps, attempting to bait Zaarin into pursuing top-secret Imperial technologies such as the newly-deployed Missile Boat. Zaarin launched several efforts to gain possession of these technologies, but his forces were repeatedly defeated by Tan Maarek Stele, who piloted the Missile Boat with great skill. Despite these losses, Zaarin was not deceived by Thrawn's ploys and retreated deeper into the Unknown Regions before Thrawn's forces could directly confront him. Undeterred by his losses, Zaarin acquired a full squadron of Missile Boats from an Imperial convoy and focused on capturing the Empire's next top-secret project: A cloaking device being tested aboard the modified CR90 corvette Vorknkx. To prevent the Imperials from developing more Missile Boats, Zaarin's faction destroyed the factories developing them in a planetary bombardment, killing thousands. This, along with the Rebel Alliance's theft of a Missile Boat prototype, the Sealion, led the Emperor to order all surviving Missile Boats placed in lockdown until further notice, shortly before Zaarin's final stand.
Ultimately, Thrawn defeated Zaarin in the Emperor's Will campaign, resulting in Zaarin's death. Thrawn exploited Zaarin's reliance on advanced technology by allowing him to escape with the cloaked Vorknkx, knowing the ship's cloaking device had a critical flaw that would destroy it upon entering hyperspace, thus ending Zaarin's coup.
Zaarin commanded a fleet composed of Star Destroyers and smaller vessels, along with several stormtrooper units. As a former TIE fighter researcher, Zaarin's forces utilized experimental models largely unavailable to loyalist Imperial pilots. He also received occasional support from the Alliance Fleet. Despite their technological advantage, they were ultimately defeated. Loyal Imperial forces designated all starfighter squadrons and most shuttle and transport craft with a "Z-" prefix for easy identification during combat. Furthermore, Zaarin's TIE squadrons were modified with shield generators, unlike those of the mainline Imperial forces.
Their vessels included Assassin-class corvettes, with at least three groups known as the Arditi group, BaKaar group, and Falcon group; Gamma-class ATR-6 assault transports such as the Oz, Ram and Divine Wind, including the Upsilon group, Z-Epsilon group, Z-Lambda group, Z-Omega group, and Z-Sigma group as well as the Elpi, the Immobilizer 418 cruisers Bomb, Harpago, Grappler and Maelstrom, Alpha-class Xg-1 Star Wing squadrons including the Mu (later Z-Mu), Z-Nu and Tau (later Z-Tau) Squadrons, and TIE/sa bomber squadrons including the Z-Alpha, Z-Beta, Z-Delta, Z-Eta, Z-Gamma, and Z-Theta Squadrons, TIE/ad starfighters including Alpha Squadron and Z-Zeta, Delta-class JV-7 escort shuttles including the Hellcat and Haven groups, Imperial-class Star Destroyers such as the Glory, Imperator and Thunderer, Nebulon-B2 frigates including the Raptor and Shadow, TIE/LN starfighters including Z-Delta and Z-Theta squadrons, at least 2 Modular conveyors which included the Cod, YT-1300 light freighters such as the Coral, at least three CR90 corvettes including the Caplure and Vorknkx, Carrack-class light cruisers including the Jumimi, Strike-class medium cruisers including the Serpent, TIE/IN interceptors including the Z-Delta Squadron, TIE/D Defenders including the Delta, Iota, and Theta Squadrons, Assault Gunboats, Muurian transports including the 500 2, assault transports, Lambda-class T-4a shuttles including the Sigma group, Beta-class ETR-3 escort transports including the Lambda 1, and various other vessels.
In addition to the standard military forces, Zaarin commanded Force-sensitives led by former Emperor's Hand Arden Lyn, who were instrumental in capturing the Emperor by combining their Force abilities to neutralize the Sith Lord.