The Imperial Core Defense Fleet was one of the earliest armadas organized at the inception of the Galactic Empire and the massive overhaul of the military. Comprised of the most powerful warships of the Clone Wars, the Core Defense Fleet was responsible for the overall defense of the Core worlds. Headquartered at Imperial Center, the Fleet was one of the largest such in the entire Imperial Navy.
At the start of the Galactic Civil War and the subsequent military build-up, the Core Defense Fleet was drastically increased in size and placed under the control of one Fleet Admiral Sinar Fenes, a veteran of the Clone Wars and a notorious anti-pirate hawk. Although the Fleet performed its duties during the war, Fenes was corrupt and had plans of his own, which he executed after the death of Palpatine, during the Battle of Coruscant. Turning rogue, the Core Defense Fleet was turned against the Empire; a significant portion of the Fleet sided with its commander and formed into the notorious Red Fleet.
After the Ambush at Todell and death of Fenes, the Core Defense Fleet was reorganized under the Interim Ruling Council and a new leader, Kenjan Sekirol, hero of the battle at Todell. However, its size was significantly decreased, and the scope of its territory was diminished greatly - focusing primarily on the Tarkin Corridor and surrounding systems.The recapture of Coruscant in 15 ABY and the Core during the Imperial Blitzkrieg saw the Core Defense Fleet once again returned to its former size and power, its territory once again returned to its pre-Endor scope.