Installation 04

''For the replacement megastructure, see Installation 04B. For the Firefight map, see Installation 04 (level)''

"Whoever controls Halo controls the fate of the universe."

- Captain Jacob Keyes

Installation 04, also known as Alpha Halo, was one of a series of gigantic ring worlds, the Halo Array, left behind by the enigmatic, technologically advanced, and apparently extinct Forerunners.

The Covenant reverentially described Installation 04 as both the First Holy Ring and the First Sacred Ring. After its destruction at the end of the Battle of Installation 04, the Ark started to construct a replacement for Installation 04.

Summary
The purpose of Installation 04, along with its brethren, was to preclude and thwart the parasite forms known as the Flood from consuming all sentient life in the galaxy by destroying all sentient life to prevent eventual consumption. In the event of a Flood outbreak, one of the seven installations could be triggered (in turn setting the rest of the array on stand-by) to annihilate all sentient life within 25,000 light years. Once one ring is set off all remaining rings would activate. All seven rings could be fired at once if need be.

Installation 04, until its destruction by the Master Chief, was controlled by the Forerunner artificial intelligence construct (Monitor), 343 Guilty Spark.

The climate of Installation 04 is very similar to Earth's climate. There have been hurricanes over the oceans on the ring. The weather is, however, extremely unpredictable - rain and snowfall can occur at random, leading some to wonder if the weather is intentionally irregular, or if it follows a pattern such as snow being deliberately made at the control room to slow the Flood.

Ancient history
Installation 04 was built by the Forerunners over 100,000 years before the Battle of Installation 04 (It was 101,217 years old in 2552 A.D., but this is measured in "local time").

The Installation was activated sometime thereafter and all Forerunner and most of the Flood were killed. Installation 04 lay dormant for a hundred thousand years, with 343 Guilty Spark and his Sentinels ready to keep the Flood confined in the Flood Containment Facilities and keeping the infrastructure of the Halo in perfect working order.

Intermediate period
Sometime after the activation of the Array, a number of space-faring species stumbled across and investigated the installation. Unlike the Covenant, these species did not manage to break containment and left the Halo without breaking containment.

Destruction
"Halo... It's finished..." "No, I think we're just getting started."

- Cortana talking to the Master Chief after the destruction of Installation 04.

The Covenant discovered the location of Installation 04 after the Covenant Fleet of Particular Justice followed the single UNSC cruiser, the, which was fleeing from the Fall of Reach through slipspace. It is assumed that the Covenant knew about the Ring prior to the events of The Battle of Installation 04, as the Prophets all have a holographic representation of them on their headdresses and Cortana stated previously that she used the coordinates received by the beam in Halo: The Fall of Reach. Due to the Covenant's faster Slipspace capabilities they arrived before the Pillar of Autumn.

The Pillar of Autumn arrived around September 19, 2552 and was promptly shot down by the warding Covenant space forces. At around the same time, the Covenant ground forces on Installation 04 accidentally unleashed the Flood from captivity. The ensuing four-day battle that took place all over the ring was called The Battle of Installation 04. Humans, Flood, and the Covenant fought massive battles against one another as the Forerunner constructs tried to control the outbreak by activating Halo. The ring's AI, 343 Guilty Spark, also known simply as The Monitor, tried to convince the Master Chief to activate Halo. Not knowing the truth of what it did, he attempted to light the Ring but was stopped by his AI friend and companion Cortana who was in The Core. She informed the Master Chief of Halo's true purpose and stashed the Index in her memory banks. The Monitor betrayed the two and tried to kill the Master Chief and retrieve Cortana, but the two escaped and started plotting against him. In the end the Master Chief detonated the Pillar of Autumn ' s fusion reactors which destroyed the Halo ring.

Only a handful of humans and Covenant survived the battle. 343 Guilty Spark floated through space until he was rescued by a group of Covenant near Threshold. Inspired by his words, they began a heretical rebellion against the greater Covenant. Installation 04's destruction is seen as the first step in the chain of events that led to the Great Schism. The Heretics were quelled by The Arbiter who silenced their leader, but the seeds of a rebellion were planted. The Monitor was then captured by the loyal Covenant and later defected to the humans' side until he was destroyed on the replacement Alpha Halo by Spartan-117 with the help of Sergeant Johnson.

Installation 04 was the first Halo installation encountered by Humans and first to be destroyed. Its destruction triggered the activation of a portal leading to a Micro Dyson Sphere on Onyx and also caused the Ark to start building a replacement ring.

There is now a large field of debris where Installation 04 was, though a few large chunks of the ring remain. Some smaller pieces of the Installation 04 have landed on Basis and others have burnt up in Threshold's atmosphere upon entry. The remaining large chunks are molten and unlikely to be capable of supporting any kind of life and are thus likely free of Flood.

According to the Halo: Evolutions story The Mona Lisa, all of the pieces of the Installation are being gradually pulled into Threshold's atmosphere where they will presumably burn up and be destroyed.

Replacement
Shortly after the destruction of the Halo, the Ark began to automatically construct a new Halo to replace Installation 04. This exact copy of the first Halo ring was nearing completion only a few months after the first ring was destroyed, but was also subsequently destroyed when it was fired before it was ready by the Master Chief and Cortana. 343 Guilty Spark attempted to prevent this, but was finally destroyed by the Master Chief with the help of Sergeant Johnson in this new ring's Control Room.

Astronomy
See full article: The Halos

The "Ringworld" of Halo is much smaller than Larry Niven's Ringworld, by a magnitude of 300,000. While the diameter of Niven's ring world is close to the diameter of Earth's orbit of 300,000,000 km, the 10,000 km diameter of Halo is much closer to the diameter of Earth itself, which is 12,756 km. The ring world has a star similar to our sun in its center, and Halo is orbiting a planet, but does not encircle it.

Speculation
It is unclear why the gas giant Threshold was specifically chosen to be the planet which Installation 04 orbited, but it is supposed that the large number of Forerunner machines already operational in Threshold (explicitly the network of Gas Mines), may have played a role in their decision. It could also be because it was the only planet in the system that had enough gravity to hold Halo in place.

Another common theory is that it was placed there mathematically in order to cover the whole of the galaxy with the spread of the Halo's main weapon. It is probable that the Forerunners had chosen Threshold as the staging point for constructing Installation 04 in a fail-safe to attempt to isolate any major Flood outbreak. It may have been as simple as its proximity to the Gas Mine stations on Threshold, which the Forerunner may have used for power.

Survivors of Installation 04
After the destruction of Installation 04, Spartan-117 and Cortana, who were responsible for the ring's destruction, fled the installation in a Longsword. Shortly afterward, they reunited with four other survivors on a Pelican. The survivors of the Battle of Installation 04 were as follows:

On a Longsword

 * Master Chief Petty Officer John 117
 * UNSC AI Cortana

On a Pelican

 * Sergeant Major Avery J. Johnson
 * Corporal Locklear
 * Lieutenant Elias Haverson
 * Warrant Officer Sheila Polaski

Other

 * 343 Guilty Spark
 * Linda-058
 * Thel 'Vadamee

Unknown
The following two Marines have been seen after having a part in the Battle of Installation 04, but it is unknown how they made it off Halo before the explosion. Note that there may have been other survivors.


 * Staff Sergeant Pete Stacker
 * Private First Class Chips Dubbo

Trivia

 * Sergeant Johnson humorously describes Installation 04 as "God's own anti-son-of-a-bitch-machine" and a "giant hula-hoop".
 * The numbering of the rings concerning the IWHBYD ring sequence is the opposite to the rings' actual installation numbers and should not be confused.
 * Except for Boarding Action and Chiron TL-34, all Halo: Combat Evolved multiplayer map are surely or possibly set on Installation 04.
 * It is possible to see falling debris from Installation 04 on Burial Mounds.
 * Other races came to Installation 04 before humanity and the Covenant.

List of appearances

 * Halo: Combat Evolved
 * Halo 2
 * Halo 3
 * ''Halo: Reach
 * ''Halo: Combat Evolved Anniversary
 * Halo: The Fall of Reach
 * Halo: The Flood
 * Halo: First Strike
 * Halo: Ghosts of Onyx
 * Halo: Evolutions - Essential Tales of the Halo Universe
 * The Mona Lisa
 * Halo Graphic Novel
 * Halo Legends
 * Origins