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, or Delta Halo as it is called by Humans, is one of the seven massive Halo fortress worlds built by the Forerunners. It is also the second Halo ring to be discovered by the Humans.

Details
Planet of Orbit: Substance

Monitor: 2401 Penitent Tangent

What happened to Installation 05 after the events of Halo 3 is unknown. The heavy damage done to The Ark could have put the Halo out of standby, or it could be unaware of the Ark's status, and still be awaiting remote activation. Its buildings seem to be more 'ancient' looking than Installation 04.

The aging of it could be due to the damage the Flood has done to it as well as the battles that take place, hinting that this is where the majority, or the most intense of the Forerunner/Flood battles took place. Some also believe that the relics found are not Forerunner, but Precursor, as the Forerunner favor metallic structures. It is also possible, that each Halo, while similar in architecture (I.E angular design, and same basic functional structures), has a different style from the next, an example being 05's Control Room having similarity to 04's Control Room in purpose, but with a new look, including a spherical shape at the center of the building. This is different from both versions of Installation 04, which look almost exactly the same (being of the same style), and have the same surroundings. However, a combination of this, and the weathering caused by battles with the Flood could be why Delta Halo's structures look so dissimilar. Structures constructed out of the same material as the Temple in the lake seem to be more resistant to the elements, as the only damage is slightly scuffed up surfaces. Otherwise, they are flawless.

The Installation may be smaller than Alpha Halo, described as being the size of a moon, rather than a planet, although the relevance of this is unknown. Whether this theorized size difference is common among Halo installations, or whether Installation 05 represents a different Halo Installation model to Installation 04, is unknown. Its should also be noted that it is unclear what the size of the moon the halo is being compared with is as Threshold's moon Basis was about 3 times the size of Earth, and Installation 04 was slightly smaller than Earth's diameter.

Its terrain, with the exception of the ice and snow-filled Quarantine Zone, is mostly lakes and jungle.

History
It is assumed that Installation 05 was built around the same time as Installation 04, around 98,665 BC. It was activated shortly thereafter by the Forerunners, 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. As of 2552, it had a record of 1.2 trillion simulated firings and one actual activation.

Flood Disaster
About 200 years prior to 2552, the Flood on Installation 05 escaped and evaded containment due to negligence on the part of the installation's Monitor, Penitent Tangent. 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, but 2401 Penitent Tangent was captured. Without it, the Sentinels of the Halo lacked a controlling intelligence and so many of the structures around Installation 05 fell into horrible conditions, and most of the Installation came to look like a jungle strewn with ruins.

At the time of the Human-Covenant War, a Gravemind was holding 2401 Penitent Tangent captive. Even with the addition of Forerunner Sentinel Majors 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 horrible 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. A battle record has been shown on Bungie.net:

Discovery
In 2552, the High Prophet of Regret, a Covenant Hierarch, discovered the location of Installation 05 during The First Battle of Earth. He made a Slipspace jump from Earth to the Halo, followed closely by Miranda Keyes' ship UNSC In Amber Clad.



When they arrived, Commander Keyes ordered the Master Chief to capture the Prophet of Regret. After fighting the Covenant in various temples and structures, the Master Chief and Cortana overheard Regret talking about activating the ring, which according to him, would start the "Great Journey." Miranda Keyes ordered the Chief and Cortana to find and kill Regret, while she and her Marines on board In Amber Clad went to the Library to retrieve the Index.

The Master Chief fought through waves of Covenant enemies onboard gondolas, through underwater structures, and more mysterious structures until he finally located Regret in a huge temple over the lake and killed him just as the Covenant city High Charity arrived with hundreds of thousands of ships. One ship destroyed the Prophet of Regret's temple, which caused the Master Chief to fall into the lake and ultimately be captured by the Gravemind.

The Battle

 * Main Article: Battle of Installation 05

After the Covenant had arrived, the Prophet of Truth ordered the Arbiter to go on Halo's surface and retrieve the Sacred Icon to enable the start of the Great Journey. The Arbiter, after fighting waves of Sentinels and a large Enforcer, finally deactivated the Sentinel Wall in order to retrieve the Index.

The Flood escaped, and were able to attack and infect much of the Human and Covenant forces on the ring, even taking control of the In Amber Clad and eventually High Charity. After fighting the Flood with the help of Rtas 'Vadumee, who had been sent into the Quarantine Zone beforehand, the Arbiter entered the Library. He found Miranda Keyes and Sgt. Johnson in the Index Chamber, and after neutralizing the pair, the Arbiter managed to retrieve the Index, believing it necessary to begin the Great Journey.

Tartarus, the Chieftain of the Brutes arrived in the Index Chamber, and told the Arbiter of the Prophet's betrayal. Tartarus used a gravity pulse from his Gravity Hammer to throw the Arbiter off the edge of the platform, and Tartarus then took the Icon, Miranda Keyes, and Sgt. Johnson to the Prophets. The Arbiter fell into the chamber of the Gravemind, where he met the Master Chief, 2401 Penitent Tangent, a Prophet Form of Regret and the Gravemind.

There they "edified" him of the true nature of the Installation. The Gravemind sent the Master Chief to High Charity in search of the Index, and the Arbiter to a location on the ring near the Control Center. By that time, Tartarus had brought the Index to the Halo's Control Room. The Master Chief fought through waves of fighting Brutes and Elites in High Charity until he and Cortana witnessed the flood-infected UNSC In Amber Clad arrive from Slipspace into the city, where it then crashed into a tower. The Chief continued through the city, until he reached a climatic battle in the Mausoleum of the Arbiter where large groups of Brutes and Elites were fighting. He neutralized both sides, and continued in pursuit of the Prophet of Truth and the Index.



Meanwhile, the Arbiter had helped support a group of besieged and betrayed Elites against the Brutes. The group of Elites and Grunts fought through a sequence of buildings and forests until the Arbiter arrived on a cliff overlooking the Control Center, where he met Rtas 'Vadumee.

Tartarus, with the unwilling help of his captive, Miranda Keyes, prepared to activate the Installation while the Arbiter rescued Johnson and helped commandeer a Scarab. He escorted the Scarab to the Control Center in a Banshee, where it destroyed the doors, enabling the Arbiter to slip inside. After the Arbiter battled Tartarus and killed him, Miranda Keyes removed the Index from the chamber, canceling the firing sequence. However, the installation had a fail-safe protocol which activated and sent superluminal signals to the other Halos, putting them on standby mode, ready for remote activation through The Ark.

Meanwhile, in space above the Installation, the Brute and Elite fleets had been fighting ever since Regret's assassination. With the threat of the Flood escaping Halo, both sides repurposed a small number of their ships to the burning of any ships trying to escape Halo. By the time Tartarus had been killed, Delta Halo was under Separatist control and the Prophet of Truth had escaped the completely Flood-infected High Charity in the Forerunner Dreadnought, with the Master Chief inside.

Aftermath
When Installation 05 was last seen, Flood were running loose as well as in High Charity and the surrounding Fleet. The Flood appeared to have been in control of the Installation and High Charity, as the Civil War of the Covenant had caused fighting between the remaining Covenant forces on the ring. The extent of the Flood control in Delta Halo after Halo 3 is unknown, since they were never known to be eradicated. With the Gravemind killed at the end of Halo 3, it is most likely that the Flood reverted to their original feral and disorganized state and would be easily controlled by the Sentinels and Covenant forces present there. It is not certain due to the unknown fate of 2401 Penitent Tangent. The UNSC AI Cortana had suggested that the Installation be destroyed via the use of a NOVA Bomb, but it is unknown if the idea was ever followed.

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 ringworld is close to the diameter of Earth's orbital 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 Ringworld has a star similar to our sun in its center, and Halo is orbiting a planet, but does not encircle it.

Images
 Image:Tanget.JPG|The Monitor of Installation 05, 2401 Penitent Tangent. Image:Jungle.jpg|Jungles and Lakes on Installation 05. Image:Argodaemon-DeltaHaloTank-1600-1200.jpg|A structure and a bridge on Installation 05. Image:Uprising.jpg|The Control Room of Installation 05. Image:Control Room3.jpg|The Control Room of Installation 05. Image:Llibraryday.jpg|The Library of Installation 05. 

Trivia

 * 2401 Penitent Tangent was the first known Monitor to be captured by the Flood.
 * The Halo 3 Multiplayer map Cold Storage is present on Installation 05.
 * Delta Halo's star is likely to be HD 108147, which coincidentally, has a small gas giant orbiting it.
 * There are six Halo 2 levels that take place on Installation 05; Delta Halo, Regret, Sacred Icon, Quarantine Zone, Uprising, and Great Journey.
 * It is unclear why Installation 05 is referred to as "Delta Halo" by human forces. Considering Installation 04 is given the monikker "Alpha Halo," a more appropriate name, as it was the second such installation to be found by humanity, would have been "Bravo Halo" or "Beta Halo"; the other set of bypassed names is "Charlie Halo" and "Gamma Halo" respectively.
 * A common theory is that the Halo array was a Precursor artifact as is The Ark. The 'reclaimed' Installation 04 was destroyed before being remade in the Forerunner motif of metal triangles.