In the opening year of the Galactic Civil War, which pitted the Galactic Empire against the newly-formed Alliance to Restore the Republic, the Alliance made an attempt to seize Grand Moff Wilhuff Tarkin while he was located within the Eriadu system. Although their efforts to capture Tarkin were unsuccessful, the Alliance forces did manage to liberate his Mon Calamari slave, Gial Ackbar. This individual would later rise to prominence as the most influential military commander in the Alliance's history.
The Rebel Alliance learned that Grand Moff Tarkin was scheduled to travel with Bevel Lemelisk to the first Death Star. Consequently, they initiated an operation with the goal of capturing both individuals. The Rebels formulated a plan to attack a group of Lambda-class T-4a shuttles, including the shuttle carrying Tarkin, which were headed towards the Nebulon-B frigate Vehemence in the Eriadu system.
To complicate any potential ambush and conceal Tarkin's presence, five Lambda-class shuttles were designated for the journey from Eriadu to the Death Star. Tarkin and Lemelisk were aboard one of these shuttles, identified by the call sign Epsilon 5. These shuttles received an escort consisting of six TIE Fighters, equally divided between Alpha and Beta squadrons. However, Tarkin intentionally reduced the number of guards, believing it would facilitate his movement and prevent unwanted attention to the Death Star's location. The shuttles departed from the Eriadu Governor's Palace, with Ackbar at the controls of Epsilon 5, and Tarkin and Lemelisk seated beside him as passengers. As the shuttles neared the Vehemence, three BTL Y-wing starfighters from Red Squadron entered the system and commenced their assault, supported by several X-wings. The starfighters engaged and eliminated the TIE fighters, while the Y-wings unleashed their laser cannons upon the escort shuttles.
Tarkin gave Ackbar instructions to evade the attack. However, Ackbar calmly deactivated the shuttle's shields, intending to allow the ship's destruction, which would result in the deaths of Tarkin, Lemelisk, and himself. Red Three identified Epsilon 5 and confirmed Tarkin's presence, prompting the Y-wings to fire precise shots that struck the shuttle's rear, sending it into an uncontrollable spin. Ackbar then mocked Tarkin, revealing his intention to deliberately cause their demise as retribution for the suffering Tarkin had inflicted upon him and others of his species. Tarkin and Lemelisk quickly abandoned the shuttle, fleeing to an escape pod and intentionally leaving Ackbar to face his likely death. They launched the pod, which spun wildly into space, and activated a distress signal. The pod was designed for a single occupant, resulting in discomfort and minor injuries for the two, including a broken nose for Lemelisk. Meanwhile, the Y-wings continued their assault on Epsilon 5 until it was rendered inoperable.
After the shuttle was disabled, the Hasti entered the system via hyperspace, carrying a commando unit, and escorted by two Y-wings from Blue Squadron. The Vehemence responded by launching nine additional TIE fighters – three each from Alpha, Beta, and Gamma squadrons – to engage the Rebel starfighters. The Red Squadron Y-wings joined Blue Squadron in battling the TIEs and providing cover for Hasti. The Hasti successfully boarded Epsilon 5, discovering Ackbar alive but finding that Tarkin and Lemelisk had already escaped. The two Imperials observed the boarding and expressed surprise that the Rebels would bother rescuing Ackbar, whom Tarkin dismissed as a "worthless alien."
Before the Rebels could focus on Tarkin's escape pod, Admiral Conan Antonio Motti arrived in the system aboard his flagship Star Destroyer, then known as the Steel Talon, even though Tarkin had not requested his assistance. The Star Destroyer began firing its turbolasers at the Rebel forces, preventing them from pursuing and capturing the escape pod. Once Ackbar had been safely removed from Epsilon 5, the Y-wings renewed their attack on the shuttle, ultimately destroying it. The Rebels then jumped into hyperspace and fled the system, leaving Motti's Star Destroyer to rescue Tarkin and Lemelisk.
The rescue of Ackbar and the knowledge he possessed regarding the Death Star overshadowed the Alliance's setback at Eriadu. He was returned to his people as Admiral of the Mon Calamari fleet. Like numerous planetary resistance groups, the Mon Calamari initially approached the Alliance to Restore the Republic with caution. However, Ackbar offered unofficial support and implicitly approved the decision of some Mon Calamari to dedicate their starships to Mon Mothma's cause.
Due to the historical significance surrounding Ackbar's rescue and subsequent recruitment into the Rebel Alliance, the event was recreated as a simulation for BTL Y-wing starfighters, with Keyan Farlander briefly participating in the simulation.
The liberation of Ackbar was initially detailed in the 1987 first edition of The Star Wars Sourcebook, which established that Ackbar was Grand Moff Tarkin's slave and was rescued when an elite Rebel force attacked Tarkin's shuttle as it embarked to the Death Star. The precise location of this conflict was not specified in that book. The battle itself first appeared in the 1994 Collector's CD-ROM edition of the LucasArts computer game Star Wars: X-Wing, serving as the last of six "historical missions" playable with the Y-wing star-fighter. This battle was later revisited in the 1995 novel Darksaber by Kevin J. Anderson. Set in 12 ABY, the book features Bevel Lemelisk recalling the event through a flashback. This novel was the first to establish the setting as the Eriadu system, a detail later confirmed in The Essential Guide to Characters (1995) and The Essential Guide to Planets and Moons (1998). A conflicting narrative of Ackbar's liberation is presented in the 2006 LucasArts computer game Star Wars: Empire at War, where Ackbar is rescued from one of Tarkin's research stations orbiting the planet Corulag. However, this version is not considered canon, as the account of Ackbar's rescue during an assassination attempt against Tarkin has been supported by several Star Wars reference books, including The New Essential Guide to Characters (2002), The New Essential Chronology (2005), and The Complete Star Wars Encyclopedia (2008).