"Whoever controls Halo controls the fate of the universe." - Captain Jacob Keyes
Installation 04, mostly referred to as Halo, is a Halo Arrary left behind by the enigmatic, technologically-advanced, and apparently extinct Forerunners.
The Covenant reverentially described Installation 04 as either the Holy Ring, or the Sacred Ring. It is the main setting of Halo SPV3. 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 stand-by) to annihilate all sentient life within 25,000 light years.
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. 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.
- “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
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. 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.
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. 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
- 343 Guilty Spark
- Thel 'Vadamee
- Installation 04 has some similarities with the Death Star from Star Wars. Both are large weapons of mass destruction situated in space, featured prominently in the first installment of each trilogy, and are subsequently destroyed by the protagonist at the end of the first installment. While absent for the second installments, partially reconstructed versions of both weapons appear in the third installments of both trilogies. To continue this link even further, in both cases, the antagonists who supervise the construction of this weapon (Darth Vader in Star Wars and 343 Guilty Spark in Halo) are defeated shortly before their weapon is destroyed. Also, in both cases, these weapons of mass destruction are seen to be much respected and beloved by the antagonists who own them.
- 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.