Installation 05

"This installation has a successful utilization record of 1.2 trillion simulated and one actual. It is ready to fire on demand."

- 2401 Penitent Tangent

Installation 05, also known as Delta Halo, is one of the massive Halo fortress worlds built by the Forerunners. The ring was formerly maintained by monitor 2401 Penitent Tangent, until his lax oversight led to the Flood's escape from their containment facilities. The Halo orbits Substance, an ice giant and the fourth planet in orbit in the Coelest system, located in the Norma Arm of the Milky Way galaxy.

The purpose of Installation 05, along with its brethren, was to preclude and thwart the parasitic Flood from consuming all sentient life in the galaxy. In the event of a Flood outbreak, one of the seven installations could be triggered 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 05 was the third Halo discovered by humanity and the second found by the Covenant. The ring became a battleground near the end of the Human-Covenant War; more importantly, it was at Installation 05 that the Great Schism, the civil war that sundered the Covenant, began. The installation was ultimately partially glassed by the Sangheili in order to prevent the Flood from escaping in the wake of the Battle of Installation 05.

Early history
"Those who built this place knew what they wrought. Do not mistake their intent, or all will perish as they did before."

- The Gravemind

Installation 05 was built by Installation 00's Foundry approximately around the same time as the rest of the Halo Array, circa 97,445 BCE. Human analysts of the 26th century believe that an extensive collection of species were brought to the installation to be studied by the Lifeworkers, as part of the Conservation Measure. Installation 05 was activated shortly after by the Forerunners at the conclusion of the Forerunner-Flood war, eradicating all sentient life in the galaxy and, presumably, destroying the Flood as well, with the exception of those specimens kept in the Halos for research. After the Array was fired, the installation was hardly peaceful, with over 32,967 simulated test firing a day. As of 2552, it had a record of 1.2 trillion simulated firings and one actual activation.

Flood outbreak
Around the year 97,227 BCE, the Flood on Installation 05 escaped and evaded containment due to negligence on the part of the installation's monitor, 2401 Penitent Tangent. It is believed that the Flood's escape was either the result of a system malfunction that was not properly addressed by Penitent Tangent or due to the meddling of visiting species. The Flood quickly grew out of control around the area of the installation's Library; the Flood were kept contained by a Sentinel wall built around the Library. Somehow, the Flood on the ring were able to amass enough biomass to create a Gravemind. 2401 Penitent Tangent attempted to control the situation, but he was captured by the recently formed Gravemind. Without the monitor, the Sentinels of the Halo lacked a controlling intelligence and so many of the structures around Installation 05 fell into disrepair, and most of the installation came to look like a jungle strewn with ruins.

Even with the addition of Forerunner Aggressor Sentinels and Enforcers, the Flood were able to remain loose, albeit contained within the Quarantine Zone by the Sentinel wall. This stalemate is believed to be the cause of the slow decline into the deteriorated condition of the structures of the installation. The Gravemind itself resided in the chamber directly below the index chamber in the center of the Library. The use of the Quarantine Zone was not a standard containment protocol, but the lack of a monitor forced Installation 05's Sentinels and other ancilla to employ unique countermeasures.

Discovery and conflict
"Miranda Keyes"

In 2551, following the Battle of Meridian during the Human-Covenant War, Stewards of the Covenant's High Prophet of Regret studied a Luminary found on the world. The Luminary revealed the location of the portal that led to Installation 00, as well as the location of each ring of the Halo Array. Regret traveled to the portal's location, unaware that his destination was Earth, humanity's homeworld. Arriving on October 20, 2552, the High Prophet of Regret ultimately fled the Battle of Earth to Installation 05 aboard his flagship, Solemn Penance. The carrier was pursued by, captained by Commander Miranda Keyes. In Amber Clad exited slipstream space near the installation on November 2, 2552; UNSC forces were deployed to the ringworld to engage Covenant forces, while Spartan-II John-117 was ordered to assassinate Regret. While Commander Keyes took In Amber Clad to the installation's Library to procure the activation index before the Covenant, John-117 located Regret at a temple on the ring. After eliminating the Hierarch, High Charity and its defense fleet—having been contacted earlier by Regret who sought assistance—arrived over the installation. Solemn Penance attempted to destroy the Spartan alongside the temple, though John-117 escaped by jumping into a nearby lake where he was captured by the Gravemind.

Meanwhile, Arbiter Thel 'Vadamee was charged with retrieving the activation index from the installation to begin the Great Journey. Following the orders of Jiralhanae Chieftain Tartarus, the Arbiter infiltrated the Sentinel wall and deactivated its containment shield to allow Covenant infantry deployment in the area. Inadvertently, this allowed the Flood to escape the Quarantine Zone. Journeying to the Library, the Arbiter encountered Commander Keyes and Sergeant Major Avery Johnson who had just retrieved the index. While engaging them, the index was taken by Tartarus and the humans were captured by his Jiralhanae forces. Following the orders of the High Prophet of Truth, Tartarus betrayed the Arbiter and cast him into the depths of the index chamber, initiating the Great Schism. The Arbiter was also captured by the Gravemind, and brought to the chamber where the Flood intelligence resided. Within the chamber, the Gravemind informed the Arbiter and John-117 of the Halo's true purpose. Using Installation 05's teleportation grid, the Gravemind sent John-117 to the orbiting High Charity and the Arbiter to the installation's Control Room to search for the index and prevent the Covenant from activating the Halo. The Flood managed to board In Amber Clad and made a slipspace jump inside of High Charity to infect the holy city. While John-117 pursued the Hierarchs and Tartarus to retrieve the index, they were able to escape with their human captives—though the High Prophet of Mercy was killed by a Flood infection form.

While Tartarus took the index and the humans to the Control Room to activate the installation, Truth abandoned High Charity aboard the city's Forerunner Dreadnought and fled to Earth to seek out the Ark. In the event that Tartarus was successful in activating the Halo, AI Cortana decided to remain on High Charity, where she could detonate the engines of In Amber Clad to destroy the installation; John-117 boarded Truth's Dreadnought just as it exited the system to eliminate the High Prophet. Meanwhile, the Great Schism resulted in the Sangheili completely abandoning the Covenant and a civil war ensuring throughout the system. Sangheili and Jiralhanae ships of the High Charity defense fleet battled each other over the installation, with both sides focusing a small number of their ships to prevent Flood-infected vessels from trying to escape the system. On the Halo, the Arbiter regrouped with Commander Rtas 'Vadum, and the two led Sangheili forces towards the Control Room. While Tartarus entered the Control Room with the index and the captured Keyes and 343 Guilty Spark, the Sangheili unintentionally rescued Johnson from his Jiralhanae captors. With Johnson operating a Scarab, the Arbiter agreed to work his him to stop Tartarus from activating the Halo. Johnson used the Scarab to destroy the Control Room's entrance and he entered the chamber, along with the Arbiter and a handful of Sangheili warriors.

Tartarus activated the Halo when Johnson and the Sangheili arrived to intervene. While the chieftain battled the Arbiter and Johnson, Keyes and Guilty Spark worked to retrieve the index and stop the activation process. The Arbiter and Johnson managed to kill Tartarus, while Keyes retrieved the index out of its chamber and the firing sequence was put on standby mode, ready for remote activation through the Ark. The battle soon ended when the Sangheili ships proved victorious over the Jiralhanae. Under the command of 'Vadum, the remnants of the Sangheili fleet sterilized the installation by glassing the Flood-infected portions of its surface, thereby preventing the parasite from leaving the Coelest system. Now allied, the Sangheili and humans eventually returned to Earth to assist with finishing off the Covenant.

Post-Covenant War
After the end of the Human-Covenant War, the Office of Naval Intelligence established Lisbon Station in orbit of Installation 05; beyond the range of the ring's automated defenses. The station's purpose was to study the Halo prior to its decommissioning. Lisbon Station is located in orbit around the ring, as the surface is considered too dangerous to house permanent settlements. The station is used as a staging point for UNSC research and artifact retrieval units. Numerous scans of the installation captured by and In Amber Clad during the Battle of Installation 05 are now the basis of several War Games simulations utilized by the SPARTAN-IV program.

At some point, unusual activity on the ring was investigated by ONI through remote surveying technology. The intelligence agency discovered strange structures that suddenly appeared on the installation's surface at key power and data junctions. ONI created War Games simulations Orion and Pegasus based off of these structures for Spartan-IVs to train in, with the intent to send these Spartans to Installation 05 to examine the structures. The Spartans were trained to deal with any possible threat from Aggressor Sentinels, Promethean constructs, or Covenant remnants that would interfere with the investigation. It was later discovered that, around these structures, the local Aggressor Sentinels suddenly became actively hostile and organized.

Environment
Installation 05 has a gravity of 1.04 Gs, and an average surface temperature of -19°C to 42°C (-2.2°F to 107.6°F). The ring's atmospheric composition is 1.01 and is largely made up of oxygen and nitrogen gas. The controlled climate of Installation 05 is similar to that of Installation 04, with varying weather conditions in different areas. Its terrain includes lakes, jungles, hills, canyons, and valleys, as well as the ice and snow-filled Quarantine Zone. Several hundred years prior to 2552, the Flood escaped the their containment on the ring. As the Flood began to spread throughout the installation, the Halo's surface was heavily altered. While the Flood was eventually contained within the Quarantine Zone, the capture of 2401 Penitent Tangent prevented Installation 05's environment from being properly maintained and its flora became overgrown on numerous Forerunner facilities throughout the installation. The installation was partially glassed by the Sangheili during the Battle of Installation 05.

The Halo's numerous dense jungles were also home to several Forerunner facilities. At least one dry desert exists on Installation 05; the desert featured a small canyon home to Forerunner outposts on either side. Human scientists have theorized that the canyon was likely used by young Forerunner Warrior-Servants that sought to demonstrate their prowess in combat arenas. During the Battle of Installation 05, UNSC surveillance unit RECON 127 discovered a dormant Forerunner vessel buried beneath an island on the ring's surface which had been carefully hidden by the Forerunners.

Structure and systems
Installation 05 is 10,000 kilometers (6,200 miles) in diameter and has a surface width of 318 kilometers (198 miles). Orbiting Substance, it is likely the installation's location over the large ice giant is a safety measure; the Halo can be plunged into the planet's high-pressure interior if deemed necessary. Installation 05's orbit over Substance is maintained by energy nodes. These power conduits are used to delicately control the direction and movement of the ring over the ice giant. Until his capture by the Gravemind, the installation's monitor was 2401 Penitent Tangent. The Control Room of Installation 05 is the site that controls many of the installation's operations. The Control Room is used to activate the installation's firing sequence. Housing vast archive complexes and research facilities, the installation's Library also contains the local activation index in the index chamber. As a result of the Flood's spread, the Quarantine Zone was a perimeter established on the Halo to prevent the Flood from spreading further. The zone was surrounded by a Sentinel wall, an encompassing structure that manufactured Sentinels to either repair the facility or engage the Flood. The entire Quarantine Zone was enclosed by a containment shield projected by the Sentinel wall. Additionally, Installation 05 maintains an automated defense system that partially extends to the Halo's orbit.

Installation 05 maintains a vast teleportation grid to allow individuals with the proper authority to quickly reach certain areas of the ring. The teleportation grid is sustained by a dense web of telemetry conduits, which are powered by generators buried in steep, narrow canyons throughout the installation. The surface of Installation 05 is home to numerous relay stations. As with the other installations of the Halo Array, Installation 05 hosts several Flood containment facilities scattered across the ring. These facilities were designed to analyze Flood samples kept in various states of development—beyond the firing of the Halo Array. The primary research facilities are located in remote regions of the installation, such as in a series of vast bogs and swamplands. Human analysts believe that the Forerunners placed the facilities in undesirable locations to discourage potential intruders. At least one facility specialized in determining extremophilic thresholds of specimens infected by the Flood; this facility was apparently maintained by an ancilla of its own. Prior to the Halo's activation, Forerunner Lifeworkers maintained several facilities—located in the ring's dense jungles—that were used to study an extensive collection of catalogued species during the Conservation Measure; the facilities were abandoned during the dark time that followed the Great Purification. Installation 05 also possessed numerous anti-gravity gondolas that allowed individuals to travel long and extensive distances.

Architecture
"You know, I think the Forerunners built these new structures around the old, to protect them, to honor them."

- Cortana, commenting on some of the structures on Delta Halo

The architecture of structures on Installation 05 follows the general Forerunner aesthetic, but has a clearly distinct style from some other installations such as Installation 00 or 04, an example being Installation 05's Control Room having similarities to Installation 04's Control Room in purpose, but with a different look—including a spherical shape at the center of the building. In addition, many structures on Installation 05, including the temple, appear to be more weathered than those on other installations, having a slightly brown-tinted gray color as opposed to the clean, pristine silver-gray surface material of most Forerunner structures.

Much of the decor within the structures of Installation 05 seems to be less practical and more ostentatious than that of Installation 04. Many of the rooms contain standing tables and basins that seem to serve a purely aesthetic purpose, perhaps at one time serving as lamps or torches. An island on Installation 05 is also home to a towering, weathered megalith, a structure that resembles other artifacts on the ring.

A curious feature on Installation 05 are the stone ruins encountered on the ring. While clearly consistent with known motifs of Forerunner architecture, the ruins seem clearly older and more primitive than most Forerunner structures, and seemingly predate the construction of the ring. They are also made of stone, as opposed to the metallic material seen on the majority of Forerunner constructs (although the Forerunners are known to have favored stone as a construction material in a number of other sites as well). This brings up the question of whether these are Forerunner structures at all, or if they were built by an even more ancient civilization or the Forerunners themselves long time before the construction of the Halo installations, and later moved to the ring for unknown reasons. Some human analysts speculate that these structures were not created by the Forerunners, but were transported to the ring for other species that were temporarily housed on Installation 05 during the Conservation Measure. Certain analysts believe that some of the stone structures were intended to fulfill a cultural purpose rather than a practical one, possibly as a memorial or tomb. Only a fraction of the installation's structures represent the older variety, as most of them are in a similar condition as on other known installations. Some of the newer structures were also built around the older ones to support and protect them, which is clearly evident in some of the spires built over the lake near the temple.

Trivia

 * There are six Halo 2 campaign levels that take place on Installation 05: Delta Halo, Regret, Sacred Icon, Quarantine Zone, Uprising, and The Great Journey.
 * The Halo 2 multiplayer maps set on Installation 05 include Ascension, Backwash, Desolation, Lockout, Relic, Sanctuary, Uplift and Warlock. The Halo 3 multiplayer map Cold Storage is the only one in Halo 3 to be set on Installation 05. The Halo 5: Guardians multiplayer maps Pegasus and Orion are set on Delta Halo.

List of appearances

 * Halo 2
 * Halo 3
 * Halo Legends
 * Origins
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo 4
 * Halo: Broken Circle
 * Halo 2: Anniversary
 * Terminals
 * Halo: Hunters in the Dark
 * Halo: Last Light
 * Halo 5: Guardians
 * Halo Mythos