A reserve fleet represented a specific kind of fleet formation within the naval forces of the Galactic Republic, a practice that the succeeding Galactic Empire also adopted. During the Clone Wars, which pitted the Republic against the Separatist Alliance, the Republic Navy consisted of twenty primary fleets; six of these fleets were stationed in the Core Worlds, serving in both defensive and reserve capacities. Jedi General Mace Windu suggested that should the Separatists triumph over the Republic at Anaxes, a key planet for starship production, a particular reserve fleet would have been jeopardized during the Battle of Anaxes.
Following the transitioned of the Republic into the Galactic Empire, the Imperial Navy maintained the practice of utilizing reserve fleets. An example of this was the 15th Deep Core Reserve Fleet, a numbered fleet within the Imperial Navy that operated from its base in the Empress Teta system. The 15th Fleet functioned as a security measure for the Deep Core, routinely carrying out patrols to combat smuggling and piracy.