The Damocles was originally developed by the Toromo Agency in Cambodia at the request of Schneizel el Britannia. The fortress remained under construction for much of the second season, completed after Lelouch vi Britannia ascends to the throne of Britannia in 2018.Damocles was first deployed to the Holy Britannian Empire , where it obliterated the imperial capital city, Pendragon, with a F.L.E.I.J.A. warhead that had its limiter removed, displaying the weapon's increased destructive yield. The Damocles then steadily gained altitude in the days after the attack, and entered the airspace of Japan during the Battle of Mt. Fuji, where it used several F.L.E.I.J.A. warheads against Britannian air forces. The Damocles continued ascending, moving over the Pacific Ocean on its predicted course. Unassailable due to its powerful Blaze Luminous, the Damocles remained unscathed during the battle.
After the completion of the F.L.E.I.J.A Eliminator during the battle, Lelouch vi Britannia, Suzaku Kururugi and several Britannian Knightmares used the weapon to cancel the detonation of one of the warheads before using a small window in the Damocles' shields to infiltrate the fortress. Inside the Blaze Luminous , Suzaku Kururugi duelled Gino Weinbergand Kallen Kōzuki using the Lancelot Albion, but Suzaku was finally defeated. Inside the fortress, Lelouch cornered Schniezel and defeated him by casting his Geass. He then confronted Nunnally vi Britannia and obtained the Damocles' main firing switch from her, ending the battle with victory for him and the Britannian Forces. He then declares himself the absolute and unopposed ruler of the world.
Emperor Lelouch, after the Battle of Mt. Fuji, placed Marrybell mel Britannia in charge of the fortress in his stead, and it is assumed that he used the Damocles to destroy and threaten any country which tried to oppose him. Prior to the plan to assassinate him, Nonette and the Glinda Knights, and Peace Mark, planned an attack on the base.
After the assassination of Lelouch vi Britannia and Marrybell mel Britannia, the Damocles was destroyed by sending it to the Sun.
- Damocles is a fictional person from Greek mythology, a courtier of King Dionysius who was given the chance to see what it was like to be king for a day. But the king arranged to have a sword hanging above the throne by merely a horse hair, until Damocles begged to be allowed to step down, and he realized that with great power, comes also great danger.
- Thus the name of the fortress itself, which was supposed to usher an era of world peace and happiness, is an ironic play on what Lelouch and the others argued all along, that true peace and happiness cannot be brought about through tyrannical rule and the constant threat of space-borne weapons of mass destruction.
- In the crossover mecha turn-based strategy game Super Robot Wars Z2: Saisei-Hen (which features Code Geass' plot among many others), the battle to stop the Damocles can play out in two different ways, depending on the player's choices. In the "normal" route - in which Lelouch betrays the Black Knights - it is actually Emperor Lelouch who controls the fortress. Ironically, it is only in the "If" route - an alternate story path where Lelouch stays with the Black Knights - where Schneizel controls Damocles. In both situations, the Damocles itself is considered an enemy unit, and can be attacked.