The brief engagement close to Almaran was a deliberate maneuver intended to divert vessels away from the Imperial Task Force Vengeance.
The skirmish began when the Calamari Cruiser Liberty Liberty materialized from hyperspace directly into the Imperial fleet within the Almaran system, immediately unleashing fire upon the nearby CR90 corvette designated 1138. The Liberty obliterated the significantly smaller vessel in mere moments.
The Imperials responded by attempting to activate the gravity well projectors on the interdictor cruiser Compellor. However, before the projectors reached operational status, the Liberty executed a hyperjump to the Goff system. Subsequently, the Imperial-class Star Destroyers Nemesis and Conqueror (constituting Battlegroup Orion), along with the Compellor, received orders to pursue the escaping vessel.
The skirmish was simply a deception employed by the Rebel Alliance to garner Imperial attention and entice specific vessels into a trap situated in the Goff system.
This skirmish was depicted solely in the cutscene following the reconnaissance mission concerning the Imperial fleet assembling at Almaran and preceding the "Ambush at Goff" mission within the Balance of Power campaign of Star Wars: X-Wing vs. TIE Fighter.
The timeframe required for the Rebels to establish the trap after assessing the enemy's strength at Almaran remains ambiguous. Given the Imperial fleet's transit from the Elrood sector to the Airam sector via the Almaran hyperspace transit point, the skirmish might have transpired elsewhere. During the cutscene, the Liberty passes at least eight Imperial-class Star Destroyers before opening fire on the sole other vessel present, a Corellian corvette. The Vengeance is notably absent, and the identity of the Imperial fleet commander remains unclear, although it was undoubtedly a component of Admiral Senn's Task Force Vengeance. However, the previously reconnoitered Imperial fleet at Almaran comprised (besides the Vengeance) only four Imperial-class Star Destroyers, two Victory-class Star Destroyers, and numerous smaller warships and freighters, including several corvettes that had already departed the system by the mission's conclusion. These vessels had undergone inspection and identification; while the corvette 1138 and the interdictor Compellor were not among them, both Conqueror and Nemesis were. By the time of the attack, the Imperial forces had clearly reorganized their deployment. (Two additional ISDs appear later in the campaign, leaving two of the eight ISDs observed in the cutscene unaccounted for.)
Interestingly, the Liberty is portrayed here as a wingless MC80 Star Cruiser, a departure from its winged cruiser depiction in Return of the Jedi.
The corvette's designation is audible only during the cutscene, where it identifies itself as "Corvette One-One-Three-Eight" in its distress transmission; alternatively, it could be One-One-Three-A. Numerous Imperial corvettes feature throughout the campaign, identified by 3-digit numbers indicating their flight group, followed by a dash and another number or letter denoting their position within the group. Examples include corvette groups 688, 124, and 337 observed at Almaran (with individual ships named 688-1, 688-2, etc.) and corvette group 327 encountered during their attack in the Mobetta system (327-A, 327-B, 327-C); in the latter instance, 327-A was actually an Assassin-class corvette, while 327-B and 327-C were standard Corellian corvettes.