Battle of Installation 05

The Battle of Installation 05, also known as the Battle of Delta Halo, was a major engagement between the United Nations Space Command, Covenant, Sentinels, and the Flood on the Forerunner ringworld Installation 05, otherwise known as "Delta Halo".

Introduction
During the First Battle of Earth, the Prophet of Regret lead a small fleet of two Assault Carriers and thirteen CCS-class Battlecruisers on an expeditionary raid that stumbled upon Earth, the strongest UNSC stronghold planet. After substantial ground, air, and space losses, Regret fled in an Assault Carrier over New Mombasa, opening a Slipspace rift and destroying the city in a devastating Slipspace cataclysm as it initiated an emergency jump to Installation 05, although how the Covenant obtained the coordinates to Installation 05 were unknown.

However, upon Fleet Admiral Hood's order, five United Nations Space Command Defense Force warships nearby Mombasa were close enough to catch onto the Assault Carrier's rift before it terminated: three UNSC Frigates, the, , and the , one UNSC Corvette, the , and one UNSC Prowler, the , were able to enter the Slipspace field, trailing the Assault Carrier.

Their shadowing, however, was not exactingly precise. Only the frigate In Amber Clad was successfully trailed the Assault Carrier to Installation 05. The prowler Dusk arrived days later near the Covenant homeworld ship High Charity, and the Coral Sea, Paris, and Redoubtable were not anywhere near the engagement because of the imprecise physics of Slipspace.

Fortification
While Regret's assault carrier hovered over the installation, deploying Wraiths, Ghosts, Banshees, and also companies of Elites, Jackals, Drones, and Grunts by means of Phantom dropships. The Covenant ground forces fortified themselves in a series of Forerunner ruins and temple structures, even establishing Shielded Plasma Cannons for further defense.

Meanwhile, the In Amber Clad trailed behind, and after the Assault Carrier moved off, Commander Miranda Keyes, captain of the In Amber Clad, ordered a platoon of Orbital Drop Shock Trooper special forces operators and SPARTAN-117 to establish a landing zone on Installation 05 to allow Sergeant Avery J. Johnson to bring in two flights of Pelicans and further expand the UNSC presence. The frigate made a quick pass-over of a segment of the ringworld, deploying a dozen Human Entry Vehicles. Six survived it into the atmosphere of the ring, and only four personnel eventually survived - SPARTAN-117 and three "Helljumpers". However, before they could land in the small ruins, they were detected by the Covenant, and SPARTAN-117 led the commandos in eliminating Covenant plasma turrets and holding the ruins against waves of Covenant troops until a Pelican could drop off an M12 Warthog LRV and a pair of Marines.

While the immediate objective for SPARTAN-117 and his Marines were to push through the Covenant-held Forerunner ruins, the overall UNSC objective for Installation 05 was to ensure that the Covenant would not activate the ring and extinguish all sentinent life in the galaxy. To do this, the UNSC had to infiltrate the Library, retrieve the Index, and safekeep it, thereby preventing the Covenant from using the Index to fire the ring.

After SPARTAN-117 and his men pushed through two Forerunner ruins, another Pelican air-dropped Resupply Canisters and a small number of Marines, refueling the UNSC offensive as they advanced through a ravine defended by Jackal Snipers and Drones, and as they reached another temple - this one with a hologram of the Prophet of Regret, who was sermonizing in a main Forerunner temple, preparing for the activation of the ring and the sublimation event of the "Great Journey". His elimination became the primary objective for SPARTAN-117, as his death would destabilize the Covenant politically and religiously. After Cortana deciphered the hologram, SPARTAN-117 and a pair of Marines battled through a pair of Covenant-held temples before reaching an open platform. At the time, the Covenant became aware of UNSC activity, and began becoming aggressive, so Commander Keyes sent several Pelicans towards the Master Chief, which air-dropped more Resupply Canisters on the platform.

The UNSC continued attacking, proceeding from the platform to gondola which took SPARTAN-117 and his remaining Marines to a heavily-defended Forerunner underwater temple which was guarded by Hunters, Stealth Elites, and Honor Guard Elites, amongst other Covenant forces. After emerging from the submerged temple, they emerged at a hilly Forerunner ruin, where Drones, Elites, and Grunts attempted to halt the UNSC advance, and Phantoms arrived with additional Covenant reinforcements.

However, the Covenant were ultimately unsuccessful: the UNSC, after clearing out the last ruins, were able to secure an LZ for a Pelican to air-drop Resupply Canisters and a team of Marines, who would aid SPARTAN-117 in the final push towards the main temple. They took a gondola towards the temple, which was attacked by Banshee fighters and Rangers, but they were still unable to prevent SPARTAN-117 and whatever remaining Marines from docking with the heavily-guarded Main Temple, destroy the Covenant turrets guarding it, and then proceeding to enter it, where the Prophet of Regret was finishing his final sermons regarding the activation of Installation 05.

Then, High Charity reverted from Slipspace over Installation 05, with hundreds and hundreds of warships, including those of the Second Fleet of Homogenous Clarity. From a distress signal from Regret, Special Operations Commander Rtas 'Vadumee planned to storm the temple by Phantom dropships in an urgent measure to kill SPARTAN-117 and defend the Prophet heirarch. However, the treacherous Prophet of Truth diverted the Phantoms, deliberately allowing the SPARTAN-II to kill Regret as part of his sociopolitical plans for the Covenant.

There was a large contingent of Honor Guards that defended the Prophet, but SPARTAN-117 was able to board the Prophet's levitating gravity chair and beat the Prophet to death, although during the fray, whatever remaining Marines that were left were killed. Shortly afterwards, a Covenant Assault Carrier repositioned over the main temple, and vaporized it with an Energy Projector in an attempt to kill SPARTAN-117 in an act of vengeance, but he jumped into the ocean, escaping the vaporization, although he was grasped by the tentacles of the Gravemind, a Flood overlord creature, and taken prisoner.

Race for the Index
While Regret had been murdered, with significant consequences to the Covenant, the UNSC and the Covenant both raced to reach the Library and seize the Index - the UNSC wanted to safekeep it and prevent the installation's activation, but the Covenant desired to use the "Sacred Icon" (the Covenant name of the Index) and bring it to the Control Room of the ring and activate the Halos.

After the death of Regret at the hands of the "Demon", Rtas 'Vadumee was furious at the Prophet of Truth for withdrawing his men, which could have saved Regret. However, Truth deliberately and wrongfully framed the Elites for their incompetence, which had led to the death of Regret. The Honor Guards of the Covenant were recomissioned, and the Brutes took over as the guardians of the Prophet heirarchs, a move that infuriated the Elites and drove an even deeper rift between the Brutes and the Elites, who had already loathed each other.

However, before either faction could reach the Library, it was shielded by the Containment Shield - an impenetrable energy shield denying access to the Library. The shield was projected by a Forerunner power generator buried within the Sentinel Wall, a large underground Forerunner complex heavily defended by Sentinels, Sentinel Majors, and even Enforcers. Numbers of Brutes, Jackals, and Grunts had already attempted to penetrate the Sentinel Wall, with pockets scattered all over the facility, all being overwhelmed by Sentinel defenders. However, the Arbiter was air-dropped by Tartarus's Phantom at the periphery of the wall in the beginning phase of a Covenant offensive to deactivate the Containment Shield, enter the Library, and seize the Sacred Icon.

After battling through the forward half of the Sentinel Wall and moving deeper through the facility, the Arbiter was able to destroy an Enforcer, and disengage the plug locks of the generator, and then physically disengage the generator out of its "cradle", powering off the Containment Shield.