The Closed Plan was a secret undertaking originally conceived by the former corporation Rayleonard and eventually enacted by Maximilian Thermidor and ORCA. Its intent was to destroy the orbiting Assault Cell satellites, thereby paving the way for humanity to migrate away from the polluted Earth and into space.
Before the National Dismantlement War, the corporations all had intentions of exploiting the last frontier: outer space. In order to hinder each other's progress, they constructed multitudes of powerful weaponized satellites called Assault Cells. These unmanned autonomous weapons orbited the Earth and served as an impassable barrier to space, destroying anything attempting to leave. Unable to reach space due to their own foolishness, the corporations prevented humanity a means to escape and migrate elsewhere.
Realizing the dangerous potential of the Kojima Particles, the very technology that gave birth to the company, and what the consequences of its widespread uses were, the Rayleonard corporation conceived a plan; defeat the other corporations, and use a number of massive land-based anti-satellite cannons to destroy the Assault Cells and clear the way to outer space.
Rayleonard was destroyed, but the plan survived in the form of ORCA led by Maximillian Thermidor. Thermidor believed passionately in the Closed Plan and its goals, stating that they must "wash away the sins of the corporations" and undo their mistake of blocking the way to space. He understood that diverting the energy of the Arteria facilities meant the Cradles would lose power and fall to the ground; he and the other members of ORCA were willing to have that blood on their hands if such a sacrifice would ensure the survival of mankind as a whole.
Ten years after the National Dismantlement War, ORCA finally moves into action. Striking at several of the Arteria facilities with a high rate of success, they spark a conflict between the League and themselves. The eventual outcome is up to what route the player chooses.
The Closed Plan can unfold in one of three ways, depending on the actions of the player in Armored Core: For Answer during the end of the third chapter:
If the player chooses to side with Wynne D. Fanchon and follow the League Path, the Plan fails. Wynne and the player eliminate ORCA, destroy the anti-satellite cannons and retake the Arteria facilities, securing their energy and the safety of the Cradles.
If the player chooses to side with Thermidor and ORCA and follow the ORCA Path, the Plan succeeds. All 12 other members of ORCA are killed, leaving the player as the sole remaining member. In a recording, Thermidor entrusts the task of completing the Plan to the player, who assaults Arteria Cranium. The player defeats the defenders Wynne D. Fanchon and Roy Saaland, securing the Cranium's energy, however Maximillian Thermidor betrays the player in same mission in Hard Mode and like in the Destruction Path assist Wynne D. Fanchon as Otsdarva. As the Cradles fall to the surface of the planet, the anti-satellite cannons charge up and fire on the Assault Cells, clearing the way to outer space.
The plan also fails if the player sides with Old King in the Destruction Path. In this path, ORCA (Maximillian Thermidor, who drops his guise and comes out as Otsdarva using Stasis) and the Collared Lynxs (Lilium, Wynne D. Fanchon, Roadie, and Kasumi Sumika in hard mode) ally and ambush the player in Occupation of Arteria Carpals to stop the genocidal Lynx and Old King from destroying the other Cradles. They fail and only manage to kill Old King, allowing the Lynx to continue taking down the Cradles to become one of the greatest monsters known to mankind.
- In the hard mode of "Attack on Arteria Cranium," it is revealed that Maximillian Thermidor was actually Otsdarva, who was supposedly killed in "Defend Line Ark" or "Destroy Line Ark." This implies that ORCA was actually created by the League in order to find the dissenters and crush them once and for all, reinforced by one of the cutscenes before ORCAs appearance that stated that the League was preparing something in secret.
- One theory: Old King's chances of survival against the four elite LYNX are extremely low, even despite fighting alongside Strayed; however, it IS possible for Strayed to defeat the elite LYNX [Plus one more in hard mode] without Old King having to die. Like White Glint's fate, its unavoidable that both Stasis and White glint are killed/disabled; eg. White Glint begins with 50% AP left, Stasis terminally "malfunctions." Furthermore, White Glint is forced to be defeated in battle regardless of the remaining AP he has, but it isn't confirmed that the Raven dies; Fiona only mentions he "can't carry on." Because of the ambiguities involved, is not known if in the Destruction Path Old King actually dies, as his fate never forced him to be killed during the mission, nor at the end; it does, however, leave him out of the dialogue during Strayed overboosting to the skies.
- The Closed Plan is identical to Char Aznable's plot in Mobile Suit Gundam: Char's Counterattack wherein he attmepted to drop Axis asteroid colony to cause a nuclear winter on Earth in order to force humanity into the colonies in outer space