Halo Alpha
Halo Alpha

This article is about Installation 04. For othe use of Installation 04, see Installation 04 (disambiguation).

Whoever controls Halo controls the fate of the universe.
— Captain Jacob Keyes

Installation 04, sometimes also referred to as Alpha Halo, was one of a series of seven gigantic ring worlds (the Halo Array from which the series gets the name) left behind by the enigmatic, technologically-advanced, and apparently extinct Forerunners.

The Covenant reverentially described Installation 04 as either the First Holy Ring or the First Sacred Ring. It is the main setting of Halo: Combat Evolved, the first game in the Halo Trilogy. After its destruction at the end of the Battle of Installation 04, the Ark started to construct a replacement for Installation 04. 343 Guilty Spark is the Monitor assigned to this Installation.


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 standby) 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 John-117, was controlled by the Forerunner Artificial intelligence construct, 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.[2] The weather is, however, extremely unpredictable—rain and snowfall can occur at random, leading Cortana 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.[3][4]



Installation 04 with Threshold in the background.

Ruined Halo Ring

Part of the wreckage of Installation 04.

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 most of the Forerunners and 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.

An unknown amount of time after the Installation was activated, a spacecraft belonging to an unknown alien race crash-landed on the ring. All inhabitants were presumably killed in the crash, as none of them ever emerged. A sarcophagus was then built around the spacecraft by 343 Guilty Spark.


“Halo... It's finished..."
"No, I think we're just getting started.”
Cortana talking to John-117 after the destruction of Installation 04.
Main article: Battle of Installation 04
H2A Cinematic I04Destruction

Halo, as it explodes.

The Covenant discovered the location of Installation 04 after the Covenant Fleet of Particular Justice followed the single UNSC cruiser, the UNSC Pillar of Autumn, 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 John-117 to activate Halo. Not knowing the installation's true purpose, he attempted to activate the Ring but was stopped by Cortana, who was in The Core. She informed John-117 of Halo's true purpose and stored the Index within her memory. The Monitor betrayed the two and tried to kill John-117 and retrieve Cortana, but the two escaped and started plotting against him. In the end John-117 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. Learning the true purpose of Halo, they began a Heretic rebellion against the Covenant. Installation 04's destruction is seen as the first step in the chain of events that led to the Covenant Civil War. 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 but later defected to the humans' side along with the Arbiter. He was destroyed on a replacement for Alpha Halo by John-117, after the monitor betrayed them by mortally wounding Sergeant Johnson, in an attempt to save this replacement from meeting the same fate as its former.

Installation 04 was the first Halo installation encountered by Humans and first of the newer Halos, created by the Lesser Ark, 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 begin construction of a replacement ring, which would be nearing completion by the 11th of December 2552.

Most of the debris from the installation's destruction was confirmed by the UNSC to have been caught by the gravitational pull of either Threshold or its moon Basis. The chunks pulled into the gas giant are thought to have burned up in entry of the planet's atmosphere, meanwhile, Basis' surface is littered with debris from the ring as shown in the War Games map known to SPARTANs as Burial Mounds. What little of the ring's detritus remained in space following the ring's destruction eventually formed a debris field that was held in Threshold's orbit.[5]

According to UNSC surveys, 30% of the ring's mass and curvature remain unaccounted for, in that it had neither been captured by the gravity of either nearby celestial body or remained in the debris field. One large fragment of the ring known as Alpha Shard, accounting for most of the discrepancy, was discovered in a system far from Soell in 2555. When the Office of Naval Intelligence received information from automated scout vehicle Recon-14, deployed by the UNSC Pillar of Autumn during its final approach to the ring, Dr Madeline Tress was the first to correctly assume that it had come from the missing fragment of the ring.[5]

The common theory on how the shard came to be is that a fail-safe mechanism was activated when the Pillar of Autumn's reactors went critical, intending to preserve the ring by initiating a slipspace jump and moving to another location. However, as the ring was critically damaged by the ensuing explosion, only Alpha Shard ever made it into slipspace and even then, it didn't follow the intended course and eventually fell out of slipspace into orbit around a red giant.[5]

Despite the harsh conditions, some life was able to survive in the remnants of the ring. 343 Guilty Spark correctly speculated that the Flood would be able to survive the installation's destruction and so petitioned Sesa 'Refumee to enact proper containment procedures, which Sesa declined to do.[6][7] Some of the surviving Flood was discovered by the Mona Lisa, an ONI-requisitioned prison transport which had been tasked with experimenting on the infection. However, nothing would come of the research as the Flood escaped containment which prompted the UNSC Red Horse to destroy the ship according to Cole Protocol.[8] In addition, several colonies of the Thanolekgolo gestalt of Lekgolo were able to survive on Alpha Shard, where they would be encountered by Jameson Locke and his team, in 2555.[9]


Main article: Installation 08

Shortly after the destruction of the ring, 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 John-117 and Cortana. 343 Guilty Spark attempted to prevent this, but was finally destroyed by John-117 with the help of Sergeant Johnson in this new ring's Control Room.

Soon after, the unfinished new Halo was fired, being self destructed nad heavily damaging the Ark.



A size comparison between Alpha Halo, The Ark, Threshold, and planets in the Solar System

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 it 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 Array'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 Forerunners may have used for power.

Survivors of Installation 04[]

After the destruction of Installation 04, John-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[]

On a Pelican[]



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.


  • Johnson states that he cares not whether it is "God's own anti-son-of-a-bitch-machine" or 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.
  • It is possible to see falling debris from Installation 04 on Burial Mounds.
  • It is possible that other races came to Installation 04 before humanity and the Covenant, as based on some of 343 Guilty Spark's logs recording on the Covenant's arrival.[10]
  • It is possible that all flora and fauna on the Halo was cultivated by Forerunner Lifeworkers prior to the firing of the array. When Installation 04 is rebuilt aboard the Ark it is stated that it is almost complete, yet all that can be seen is barren molten metalwork.
  • Like all Halo Arrays, Installation 04 get its power from the Power Rooms which are connected to other Power Rooms placed around the whole ring. A power room on Installation 04 featured a large vertical Core and a dome-shaped roof, with large glass windows that run down the side. The energy which powers the Installation can be seen pulsating up through the core and then back down through the windows.