During the twenty years preceding the Galactic Civil War and the length of that conflict, as well as during the era of Imperial remnants, the mainstay of various Imperial fleets and battlegroups was the Imperial-class Star Destroyer. There were two variants of this class:
Late in the Old Republic Era, the Republic Navy saw a need for a more powerful breed of battleship to combat the increasing firepower of the Separatist fleet. As a result, various developments were made in naval power and strength, including the Imperial-I class Star Destroyer. 1,600 meters in length and bristling with a vast array of weaponry, these ships were the successor of the Venator-class Star Destroyer that had served as the mainstay of the Republic armada for the majority of the ongoing Clone Wars. Following Sheev Palpatine's declaration of the Republic's transformation into the Galactic Empire, the Imperial-I became a symbol of the cruelty, oppression and strength of the new order.
Between the destruction of the Death Star I and the Battle of Hoth, the Imperial Navy saw that the Imperial-I class would not be adequate to suppress the rebellion. In addition to this, continued developments in starship technology had helped render many parts of the Imperial-I that had once been considered technological marvels into obsolete machinery. As a result of this, the fleet decided to launch the Imperial-II, a ship of the same length as the Imperial-I that featured stronger shields and weaponry in addition to various subtle enhancements. These ships, much like the Imperial-Is, became symbols of tyranny as they were deployed in various actions to halt the growing influence of the Alliance to Restore the Republic. Following the death of Palpatine and hundreds of the Empire's best and brightest at the Battle of Endor, the reduced manufacturing power of the Imperial remnant meant that the ships that survived the campaigns of the fledgling New Republic became enviable parts of the fleets of various warlords and restorers of the Empire.