The Exile fleet consisted of Sith personnel carriers which escaped the collapsing Sith Empire after the Great Hyperspace War concluded, and the counterinvasion began. For almost twenty standard years, the fleet journeyed through the Unknown Regions, ultimately arriving at the long-lost Sith planet of Dromund Kaas. This planet then became the new base of operations for the reconstituted Sith Empire.
In 5000 BBY, following the Great Hyperspace War's end, the victorious Supreme Chancellor Pultimo of the Galactic Republic initiated a counterinvasion targeting the Stygian Caldera. The goal was to completely destroy the Sith Empire and eliminate any lingering threat to the Republic's security. During this campaign, Vitiate, the secluded Sith Lord of Nathema, began transmitting messages of hope to the Empire's crumbling remnants. Promising guaranteed victory, Vitiate gathered the remaining Sith Lords of the old Empire on Nathema, then performed a dark-sided ritual which drained the life force of the Sith, granting him practical immortality.
Vitiate, now calling himself Sith Emperor, assembled a fleet of Sith personnel carriers filled with young Sith survivors. In 4999 BBY, this exile fleet left Korriban, heading for Dromund Kaas, a forgotten Sith colony recently found by Vitiate's chief researcher on Nathema. However, to ensure the rising generation of Sith were completely obedient and dependent on him, the Exile fleet wandered aimlessly through deep space for nearly two decades, making random hyperspace jumps.
After this long journey through the Unknown Regions, the exile fleet finally reached the lost world of Dromund Kaas. There, hidden within the planet's jungles and rainforests, the surviving remnants of the old Sith Empire plotted their revenge and return to the galaxy, reforming into a reconstituted Sith Empire under Vitiate's complete control. Under the direction of Odile Vaiken, a Grand Moff who began as a navigator and pilot on the exile fleet's ships, a plan to create a new Imperial Navy was initiated, leading to the development of a new Imperial armada over centuries.