Gnisnal, designated as SD-489 by the Rebel Alliance, was an Imperial I-class Star Destroyer serving within the ranks of the Imperial Starfleet.
During the chaotic evacuation of Narth and Ihopek, Gnisnal experienced a critical malfunction. Specifically, its main transfer coupling for the solar ionization reactor suffered a failure, triggering the initial blast. Subsequently, the hyperspace motivator imploded into the reactor core, resulting in a second explosion that fractured the ship's hull and obliterated decks 1 through 26. The vessel then broke apart into multiple substantial fragments, left abandoned in space.
As part of the initiative known as Operation Flotsam, the New Republic deployed the retrofitted fleet tender Steadfast to search the wreckage for useful materials or intelligence. The crew located an undamaged and functional datacore on Level Ninety-Six, specifically in Corridor Q. This section was still energized by backup power cells (Number Eight supporting Number Four). The datacore's data provided the Asset Tracking office with its initial, though outdated, Imperial Order of Battle, which subsequently enabled the discovery of the Black Fleet.
The name Gnisnal (which is "Lansing" in reverse) originates from Lansing, Michigan, the city where Michael P. Kube-McDowell, the author of The Black Fleet Crisis, resided while writing the novels Before the Storm and Shield of Lies.