Battle of Installation 05

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"Cortana, what exactly am I looking at?"

- Commander Miranda Keyes

"That... is another Halo."

- Cortana

The Battle of Installation 05, also known as the Battle of Delta Halo (or the Battle for the Second Ring of the Gods among the Covenant, ), 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
At the beginning of the Battle of Earth, the Prophet of Regret led 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, as well as the home world for humanity. 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, inside the Earth's atmosphere, to Installation 05. How the Covenant obtained the coordinates to Installation 05 is unknown.

However, upon Fleet Admiral Hood's order, five United Nations Space Command warships near New 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 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 nowhere near the engagement, most likely due to the imprecise physics of Slipspace and the UNSC's rather limited technology in that field.

UNSC Offensive
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 Troopers and SPARTAN-117 to establish a landing zone near a series of ruins and temples on Installation 05 to allow Sergeant Major 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 (HEV). Six survived the atmosphere of the ring, and only four personnel eventually survived the impact - 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 their position 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 was to push through the Covenant-held Forerunner ruins and capture the Prophet of Regret, the overall UNSC objective for Installation 05 was to ensure that the Covenant would not activate the ring and extinguish all sentient life in the galaxy. To do this, the UNSC had to infiltrate the Library, retrieve the Index, and safeguard 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. They proceeded to another temple, this one with a hologram of the Prophet of Regret, who was sermonizing in a main Forerunner temple to prepare for the activation of the ring and the sublimation event of the "Great Journey". After learning all of the information the Prophet could provide, 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 a gondola which took SPARTAN-117 and his remaining Marines to a heavily-defended Forerunner underwater temple which was guarded by Hunters, Stealth Elites, Honor Guard Elites, Stealth Grunts, and 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.

Assassination
However, the Covenant were ultimately unsuccessful. The UNSC, after clearing out the last ruins, were able to secure a landing zone for a Pelican to air-drop Resupply Canisters and a team of Marines, who aided SPARTAN-117 in the final push towards the main temple. The UNSC forces commandeered a gondola they found on a tower. Despite being attacked by Covenant Banshees and Rangers, they were able to gain access to the temple. After destroying several defense turrets, they entered the Temple as the Prophet of Regret was finishing his sermon.

After docking, High Charity reverted from Slipspace over Installation 05, with hundreds of warships, including those of the Second Fleet of Homogeneous Clarity. Responding to 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 leader. However, the treacherous Prophet of Truth diverted the Phantoms, deliberately allowing the SPARTAN-II to kill Regret as part of his socio-political plans for the Covenant.

"How dare you interrupt my sermon? Guards, remove him! Your very existence offends me, Demon!"

- Prophet of Regret

A large contingent of Honor Guards and Grunts defended the Prophet, but SPARTAN-117 was able to board the Prophet's levitating gravity chair and beat the Prophet to death. During the fray, all the remaining Marines were killed. Shortly thereafter, a Covenant Assault Carrier repositioned over the main temple, and destroyed it with a gravity beam, but SPARTAN-117 jumped (or fell) into the lake with seconds to spare and was grasped by the tentacles of the Gravemind, a Flood overlord creature, and taken prisoner.

Introduction
"You will journey to the surface of the ring, and retrieve this Sacred Icon. With it, we shall fulfill our promise, and begin the Great Journey."

- Prophet of Truth to the Thel 'Vadam

After the Prophet of 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 keep it safe to prevent the activation of the installation, but the Covenant desired to bring the "Sacred Icon" (the Covenant name of the Index) to the Control Room of the ring and activate the Halos.

Changing of the Guard
"Recommissioning the guard was a radical step, but recent events have made it abundantly clear that the Elites can no longer guarantee our safety."

- Prophet of Truth to Rtas 'Vadumee

After the death of Regret at the hands of the Demon. Rtas 'Vadumee was furious at the Prophet of Truth for withdrawing his men, who could have saved Regret. However, Truth deliberately and wrongfully framed the Elites for the death of Regret. The Honor Guards of the Covenant were decommissioned, and the Brutes took over as the guardians of the Prophet hierarchy, a move that infuriated the Elites and drove an even deeper rift between the Brutes and the Elites, who were already mortal enemies.

Containment Shield
"Once the shield is down, we'll head straight to the Library. I do not wish to keep the Hierarchs waiting."

- Tartarus to the Arbiter

However, before either faction could reach the Library, it was shielded by the Containment Shield - a recognized impenetrable energy shield denying anyone 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.

"You've reached the power source. Overload the locks holding it in place. Release the power source. Now, find a way to remove it from its cradle."

- Tartarus to the Arbiter

After battling through the forward section of the Sentinel Wall and moving even 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. While the shield had been disengaged, the path to the Library was far from clear. There was a rampant Flood infestation: the second half of the Sentinel Wall was heavily saturated with Flood, and there were icy canyons heavily entrenched by Flood battling against outnumbered Sentinel defenders that lay between the perimeter of the Containment Shield and the Library, which was accessible only by an underground gondola.

"Blasted machines! Make your own a way through the wall, Arbiter!"

- Tartarus to the Arbiter

Tartarus attempted to pick up the Arbiter and head directly for the Library, but his Phantom was engaged by an Enforcer, forcing the Arbiter to battle through through the warring Flood and Sentinels that resided in the Flood-Infested Wall by himself. However, the Arbiter was not alone - the UNSC had dispatched a squad of Marines to also fight through the facility, but they were overwhelmed by the Flood, leaving a trail of crumpled bodies throughout the facility and fueling the Flood's ever-growing army. The Covenant apparently sent a small team of three Special Operations Elites to clear out the lower levels of the complex, but these too were killed. Finally, the Arbiter jumped down a series of plummeting vertical tunnels, exiting from the Sentinel Wall and entering the battle-torn icy plains of the Quarantine Zone.

Battle of the Quarantine Zone


"The Flood are upon us!"

- Special Operations Elite

"We must hold this camp until reinforcements arrive."

- Special Operations Commander Rtas 'Vadumee

The Quarantine Zone was supposed to be a location where during times of war, the Sentinel custodians of the installation could herd the Flood, and prevent them from entering the Library. Two Sentinel Constructor Factory ships hung in the air, deploying Sentinel reinforcements. However, the Quarantine Zone was compromised by the Flood, and the Flood managed to crash one of the floating factories, sending it plummeting down to the ringworld.

The Covenant shortly established a "camp", air-dropping seven drop pods that contained Rtas 'Vadumee and six Special Operations Elites, along with several plasma turrets and a deployable gravity lift tower.

"We shall cut into the heart of this infestation, retrieve the icon, and burn any Flood that stand in our way! Forward, warriors, and fear not pain or death. Go, Arbiter, I'll follow when our reinforcements arrive."

- Rtas 'Vadumee

The Arbiter met with three of the Elites just outside of the Sentinel Wall, and together, they defended a small hill from the Flood before pushing inwards, where the Special Operations Commander had landed and established a small outpost, complete with turrets and the gravity lift tower, where the Special Operations force held out against waves of Flood attacks from the cliffs before they were reinforced by a pair of Phantoms that dropped off a Spectre and a pair of Ghosts. The Covenant were able to use these vehicles to advance through a large indoor Forerunner facility before entering the first of a series of expansive outdoor arctic canyons. Despite the prowess of the Special Operations Elites and the Arbiter, the UNSC were swifter to advance through the Quarantine Zone - the In Amber Clad deployed a Pelican dropship that cruised above the battling Flood and Sentinels, cutting directly towards the Library while the Arbiter and his men were forced to fight through waves of Flood, including Flood-commandeered Ghosts, Warthogs, Wraiths, and Scorpions, while all the while, Enforcers rained heavy fire.

"Arbiter, I'm sending some of my best fighters to assist you. Do not squander their talents."

- Rtas 'Vadumee

The small Covenant task force was forced to debark from its vehicles as they transgressed the wreckage of one of the Sentinel Constructor Factories, although just beyond the wreckage on the other side, they were met by another Covenant Phantom, this one dropping off a Spectre manned by Rtas 'Vadumee himself and another Special Operations Elite. However, as they progressed through the last series of snowy plains, they were met with increasingly heavy resistance as they neared the Library. The Sentinels were in much larger force, while a large number of Flood-infested humans savagely held a barricade against the Library, using crates, turrets, and heavy weapons to prevent anyone to gain entrance to the Library and retrieve the Index, which would eventually lead to the extermination of the Flood.

Library
"More humans...they must be after the icon."

- Rtas 'Vadumee to the Arbiter

However, a small UNSC Marine force led by Miranda Keyes and Avery J. Johnson was able to slip through, and in the end, the Arbiter, Rtas 'Vadumee, and half a dozen Special Operations Elites were able to slip into the periphery of the Library. There were a pair of gondolas, that when activated, autonomously brought their passengers into the upper tiers of the Library, where the Index was kept. While the UNSC was first able to seize a gondola, the Covenant were close behind. However, when the Flood began to screech, alerting the Covenant that they were in full force in the bowels of the Library, Rtas 'Vadumee took a pair of Special Operations Elite, holding them at the entrance to the gondolas to defend the rest from the Flood as the Arbiter took four Special Operations Elites on the second gondola, trailing behind the UNSC-held one.

"Humans! I'll get them."

- Tartarus

"That fool! He'll alert them to our presence!"

- First Special Operations Elite

"Look on the bright side, maybe if we're lucky, they'll shoot him down!"

- Second Special Operations Elite

The gondola's ride, however, was harrowing. Flood entered the gondolas, jumping from the upper levels and also crawling in underneath on their undersides, assailing both the UNSC troops and also the Arbiter and his quartet of Special Operations Elites. Tartarus, in his Phantom, attempted to provide cover fire for the Arbiter, using the three plasma cannons of his dropship to burn off any Flood on the upper levels of the Arbiter's gondola, but later, Tartarus chased after the UNSC-held gondola.

"Behold, the library of our lords!"

- Special Operations Elite "The humans are already inside, Arbiter! After them! I'll watch the perimeter. Hurry, Arbiter! Get the icon!"

- Tartarus

"We shall protect this vessel. It may be our only means of escape."

- Special Operations Elite

Finally, both gondolas ascended to the top levels of the Library, although the UNSC one arrived first, and a small UNSC force of six soldiers (four Marines (including Perez and McKenzie)) led by Miranda Keyes and Avery Johnson, entered. Although many Combat Forms had been exhausted in the Flood's last-ditch attempt to stave off the gondolas, there were a large number of Infection Forms prowling the Library which killed off the four UNSC Marines as Keyes and Johnson advanced towards the core of the Library. Meanwhile, the Arbiter silently snuck in behind them.

"McKenzie, Perez, how's our exit? You hear me, Marines?...we got trouble."

- Sergeant Major Avery J. Johnson

Miranda stretched over a seemingly bottomless chasm, grasping for the Index, and then barely making it, securing it on her belt. Meanwhile, Sergeant Johnson shouted for the remaining Marines to report. When there was no response, the pair of UNSC personnel cautiously began to edge away from the core, with Johnson lifting his BR55 Battle Rifle at the ready while Miranda hefted her pair of M7/Caseless Sub Machine Guns. However, the Arbiter engaged his active camouflage, cloaking himself as he lunged at Johnson, head-butting him into unconsciousness, and as Miranda fired a spatter of bullets from her submachine guns, the Arbiter disarmed her, but before she could react, Tartarus entered with four of his Brute Captains. Tartarus used his Gravity Hammer, the Fist of Rukt, to stun Miranda and gravitationally levitate her towards him, draping her over his shoulder and then clasping the Index and securing it for himself.

"The Icon...is my responsibility."

- Arbiter

"Was your responsibility. Now it is mine. A bloody fate awaits you and the rest of your incompetent race. And I, Tartarus, Chieftain of the Brutes, will send you to it!"

- Tartarus

"When the Prophets learn of this, they will take your head!"

- Arbiter

"When they learn? Fool, they ordered me to do it."

- Tartarus

With the Library clear and devoid of hostiles, the Arbiter demanded to have the Index, as he was personally ordered by the Prophet of Truth to secure it for the Covenant. However, unbeknownst to him, he had been betrayed by the Prophets, as had the entire Elite race. The Prophets had made the Brutes their champions, casting aside the physically inferior Elites.

Tartarus refused to give the Sacred Icon to the Arbiter, and instead, his Brute Captains leveled their Brute Shots at the Arbiter as Tartarus revealed the betrayal. The Arbiter jerked his neck up in horror as Tartarus swung his Gravity Hammer, sending a gravitic shock that sent the Arbiter into the bottomless chasm above which the Index was once situated.

This event turned out to be a disaster for UNSC forces at the Library. Not only were most of the marines slaughtered by the Flood and Tartarus, they lost a lot of vehicles and equipment to the Flood but the worst part was In Amber Clad falling into the Flood's hands, enabling them to capture High Charity later.

"The release of the parasite was unexpected, unfortunate. But, there is no need to panic. In truth, this is a time to rejoice. A moment that all the Covenant should savor...for the Sacred Icon has been found. With it, our path is clear, our entry into the Divine Beyond guaranteed! The Great Journey is nigh...and nothing, not even the Flood, can stop it!"

- Prophet of Truth

Meanwhile, Tartarus brought the Sacred Icon to High Charity, where the Prophet of Truth exulted him and encouraged the Covenant to celebrate, for the Sacred Icon was secure, and that soon afterward, that the Halos would be fired and the Great Journey would be brought upon the Covenant.

Introduction
However, the Covenant would not activate the Halos unimpeded. The Flood, who would be starved if the rings were activated, would soon attack the Covenant to prevent the activation, and the UNSC, who understood that all sentient life would be erased, also opposed the Covenant. Later, after the fragmentation of the Covenant into the Covenant Loyalists and the Covenant Separatists, the Separatists would understand the true intent of Halo and attack the Loyalists to prevent them from activating the ringworld.

"There is still time to stop the key from turning, but first it must be found. You will search one likely spot, and you will search another. Fate had us meet as foes, but this ring will make us brothers."

- Gravemind to SPARTAN-117 and The Arbiter

Meanwhile, SPARTAN-117, who had fell into the lake, and the Arbiter, who had been thrust into the chasm of the Library, were both caught by plant-like tentacles and grabbed into the lower reaches of Installation 05, where they met face-to-face the Flood central sentient intelligence known as the "Gravemind", along with the Prophet of Regret and 2401 Penitent Tangent, the monitor of Installation 05. The Gravemind than explained to the Arbiter why the Halos must not be activated for the interests of galactic life. The Gravemind, holding both SPARTAN-117 and the Arbiter prisoner, explained that in his plan to prevent the activation of Installation 05 by the Covenant, he would manipulate Halo's teleportation grid, sending SPARTAN-117 to High Charity to search one likely spot where the Index was placed, and sending the Arbiter to the cliffs just beyond the Control Room, another likely spot.

Battle of High Charity


"The demon has entered the council chamber? Protect the Hierarchs! Seal the exits!"

- Tartarus

SPARTAN-117 was teleported by the Gravemind directly into the High Council Chamber of High Charity, where the Prophets of Truth and Mercy addressed the Covenant that the Sacred Icon was secure. Before SPARTAN-117 could kill both Prophets, they escaped by means of an elevator, while the doors were locked and waves of Honor Guard Brutes, Minor Brutes, and Grunts entered in an attempt to kill the supersoldier. Cortana managed to unlock the doors, and SPARTAN-117 chased through two towers and a set of corridors in pursuit of Truth before Cortana picked up the IFF transponder signals of UNSC Marines - prisoners of the Covenant being kept in two brigs in a multitiered detention block.

"Wait a minute! I'm reading Marine IFF transponders. The signals are originating somewhere below your position!"

- Cortana to SPARTAN-117

Cortana managed to reverse a central gravity lift, allowing SPARTAN-117 to enter the detention block. However, Tartarus had anticipated this, increasing security around the brigs while a massive firefight ensued as SPARTAN-117 released five Marines from two brigs, who assisted SPARTAN-117 in his pursuit of Truth to kill him and secure the Index.

"The Elites have failed to protect the Prophets, and in doing so, have put all our lives at risk. Let no warrior forget his oath, 'Thou, in faith, shall keep us safe, whilst we find the Path'. With my blessing, the Brutes now lead our fleets! They ask for your allegiance, and you shall give it."

- Prophet of Truth

However, meanwhile, the Covenant splintered in minutes after SPARTAN-117 emancipated the captive Marines. The Prophet of Truth made an epic announcement, and in three sentences over the loudspeakers of High Charity, put his plan to betray the Elites into action: he ordered all of the Covenant to follow the Brutes as their military commanders, and inevitably, the Elites, seething in hatred against the Brutes, took this as their final straw. Slighted by the Prophets, the Elites burst into full-out warfare on High Charity and across the rest of the Covenant empire against the Brutes. While the Grunts and Hunters followed the Elites, the Jackals and the Drones supported the Prophet-blessed Brutes. Warship crewmen began to open fire upon each other with small arms, and the Covenant fleets began to open fire against each other.

Truth's transmissions, however, allowed Cortana to triangulate his position, allowing her to direct SPARTAN-117 and his Marines in their hunt for the Prophet. The Covenant attempted to stop Cortana, but were unable to prevent her.

As SPARTAN-117 and the Marines reached the Hanging Gardens A, the first scene of Covenant fratricide was seen, as Honor Guard Elites, Minor Elites, Hunters, and Grunts fought against Brutes and Jackal Snipers amongst the massive insectoid plants. SPARTAN-117 and his men advanced to the Mid-Tower, where Rangers and Special Operations Elites entered the fray, and the Brutes unleashed their Drones into the combat.

Even as the imprisoned Marines were freed, the crew of the In Amber Clad were in peril. It appeared that the Gravemind double-crossed the UNSC, sending SPARTAN-117 hunting for the Index in the bowels of High Charity while the Gravemind teleported Flood forms into the UNSC frigate, overpowering the crew and seizing it. The Gravemind then teleported the In Amber Clad from the atmosphere of Installation 05, sending it into a Slipspace reversion over High Charity, where it plummeted uncontrollably, crashing into the Far Tower.

"Once the towers are clear, we'll drive them from the lower districts!"

- Tartarus

However, by the time that the small UNSC squad entered Hanging Gardens B, Covenant Separatist resistance on High Charity had broken. In the second Hanging Gardens, the Covenant Separatists fell back, leaving behind large numbers of Stationary Shield Generators, abandoning numbers of Grunts to berserk Brutes as the Elites fell back to the Far Tower and the Mausoleum of the Arbiter, drawing a last line of defense there. In the forward sections of the Far Tower, the Separatists held a choke-point bridge with a pair of plasma turrets, Special Operations Elites, and a pair of Hunter warriors. In the Mausoleum of the Arbiter, Specialist Ultra Elites and Hunters fought against waves of attacking Brutes. Despite their efforts, the Prophets of Truth and Mercy, Tartarus, and a handful of Brute Captains were able to tunnel through the last Separatist defenses to the far docking bays of the Far Tower. SPARTAN-117 pursued Tartarus, fighting through the Far Tower and the Mausoleum of the Arbiter to make it through to the Phantom pads.

"Your pal. Where's he going?"

- SPARTAN-117

"Earth...to finish what we started. And this time, none of you... will be left behind..."

- Prophet of Mercy's last words

The SPARTAN was too late, however. The Prophet of Truth ordered Tartarus to use the Sacred Icon in the Control Room of Installation 05, and activate the Halos. Tartarus took a detachment of Brute Honor Guards along with him in two Phantoms, along with UNSC prisoners Avery Johnson and Miranda Keyes. Truth and Mercy took a third Phantom to the Forerunner Ship - the central energy source of High Charity, and also a fully functional starship that the two remaining High Prophets were going to use to reach Earth, and "finish what The Prophets started".

Meanwhile, the Flood were escaping from the crashed hulk of the In Amber Clad. They seeped out of the rents in its hull armor, and also exhibited unexpected intelligence, commandeering its Pelican dropships and sending them over the surface of High Charity, crashing into the floors and releasing Combat Forms, and spilling Infection Forms out of the air from opened hatches. The Prophet of Mercy was beset by an Infection Form and died before he could reach his Phantom. However, Tartarus and Truth were able to depart before SPARTAN-117 could arrive.

"That structure at the center of the city! It's a Forerunner Ship...and Truth is heading straight for it! If he leads the Covenant fleet to Earth, they won't stand a chance. You have to stop him!"

- Cortana to SPARTAN-117

Despite the fact that SPARTAN-117 had failed to capture the Prophet of Truth before he could depart in his Phantom for the Forerunner Ship, it was still imperative that the SPARTAN chase after him and kill him, as if he marshaled the Covenant fleets to Earth to finish whatever he planned, the already besieged Earth would inevitably fall, despite the UNSC's best efforts. Just then, a Pelican crashes on the balcony, and some familiar creatures run out of the ship.

By that time, Covenant Separatist resistance had completely shattered on High Charity. There were none to little Elites nor Hunters remaining, and only several scattered Grunts. The Loyalists, however, retained a large number of Brutes, Jackals, and Drones. Despite the lack of a Separatist ground force, they were still very much present in space, where the Covenant fleets over High Charity had splintered in allegiances, with Elite and Brute ships actively engaging and destroying each other.

While Truth was taking a Phantom to the Forerunner Ship, Cortana detected an energy conduit to the ship located in the Mausoleum Tower ahead of SPARTAN-117's position. However, High Charity had become horribly twisted within minutes: an insidious Flood presence spread surprisingly quickly through the planetoid, disrupting power, creating a dark, gloomy atmosphere, spreading Flood spores into the air, covering large parts of High Charity in Flood biomass, and sending Flood forms all across the city-space, where the Flood fought to take High Charity from the remaining Covenant Loyalist forces.

SPARTAN-117 entered the Mausoleum Tower from the Phantom landing pads, battling through unlit, tight corridor ways where numerous Flood combat forms engaged outnumbered Brutes and Jackals, and strange Flood biological growths began to sediment against the walls. Meanwhile, the Prophet of Truth sent broadcasts throughout the city, urging the remaining Loyalists that the Covenant would prevail against the Flood while the Gravemind manipulated the loudspeakers, proclaiming that the Flood would infest High Charity and send the Covenant to their graves. SPARTAN-117 cut across the massive interior of the Mausoleum Tower, moving to the north face of the tower and making his way along a peripheral convoluted corridor to the eastern end of the tower, where he took a Gravity Lift to access the Inner Sanctum: the personal quarters of the Hierarchs.

There, a line of Honor Guard Brutes and Jackals had made a final stand against the Flood upon the gold-rimmed doors that sealed access to the Inner Sanctum. However, large amounts of Flood began to attack, and SPARTAN-117 was forced to destroy all the Covenant and Flood before entering the Inner Sanctum, and taking an adjacent Gravity Lift to a large outdoor room that hosted the viridian energy conduit to the Forerunner Ship. SPARTAN-117 was able to jump in the conduit just in time, barely making it to the ship before it lifted off for Earth. However, Cortana stayed behind: while SPARTAN-117 would attempt to neutralize the ship before it rallied the Covenant fleets at Earth, there was another danger: Tartarus still had the Index, and was about to activate Installation 05 shortly. In the event that he was about to trigger the Halos, Cortana announced that she would detonate the fusion reactors of the In Amber Clad, just like she had done to the UNSC Pillar of Autumn at Installation 04, and the blast would destabilize the ring and prevent the activation of the Halos.

Shortly afterward, all Covenant resistance on High Charity broke and succumbed to the Flood, who had infested surprisingly large amounts of the planetoid even during the raging combat between the Covenant and the Flood. Cortana, who resided in High Charity's computer systems to be ready to detonate the frigate's reactors as a final failsafe, was captured by the Gravemind, although her eventual fate, and that of the Gravemind and High Charity, is unknown, thus concluding the Battle of High Charity.

Uprising
The Covenant politico-military fractures were not restricted to High Charity: they extended to military units across the Covenant, including those on the surface of Installation 05. Upon Truth's order that the Brutes were now the ruling caste of the Covenant, Tartarus ordered the execution of the Elite Councilors, who had been gathered in the Control Room of Installation 05 for the consecration of the Sacred Icon before the Halos were fired. While most of the Councilors were murdered in cold blood, a small number were taken prisoner by the Brutes. The rest of the Covenant garrison, however, was not so fortunate. A CCS-class Battlecruiser hovering close to the Control Room was taken by the Brutes from the Elites, and a large number of Minor Elites and Grunts stationed in the cliffs above the Control Room were killed. However, there was still a number of Grunts that managed to resist, although they were terrified by the murders of their Elite superiors and Grunt comrades.

Meanwhile, Tartarus took his two Phantoms from High Charity to the surface of Installation 05, with himself, the Sacred Icon, and Miranda Keyes in one dropship, and Johnson and two other anonymous Marine prisoners. Tartarus debarked from his own Phantom onto the Control Room, with Keyes and the Index in his grip. The other Phantom diverged, however, and by unknown means, the three Marines freed themselves from their Phantom aboard the docking platform. Avery J. Johnson was able to seize control of the docked Scarab while the other two Marines fought off a large number of Brute Captains with Plasma Pistols.

However, there was soon a reorganized resistance movement: the Gravemind teleported the Arbiter to a high cliff south of the Control Room, and gave him an objective: to prevent Tartarus from using the Sacred Icon and activating Halo, which would not result in the promised sublimation event of the Prophets, but only death and destruction on a galactic scale. The Arbiter arrived just too late, witnessing the murders of a handful of Elites from afar at the hands of the Brutes, but was able to push forward against a number of patrolling Brutes, and met with an Energy Sword-armed Special Operations Elite. They were able to clear a landing zone for a number of Covenant Drop Pods, and soon, they were reinforced by a Zealot and a pair of Minor Elites. The Elites swore vengeance against the Brutes for the murders of their brothers, and led by the Arbiter and the recklessly aggressive Zealot, the Elites pushed northward through a large Brute-held Forerunner structure, unpinning small groups of scattered loyal Grunts and killing dozens of Brutes, Jackals, and Drones. Afterward, they emerged from the structure, and still perusing vengeance, mounted Ghosts, tearing through a large, convoluted canyon, fighting against Loyalist resistance: a Spectre, several Ghosts, and large numbers of Brutes and Jackals, including Jackal snipers with the help of several Separatist Grunts. It appears that the canyon-stationed forces were unprepared for an assault, as they had many unmanned Ghosts that were easily used by the Separatists to gain a swift advantage.

Later, the Loyalists eventually readied themselves, setting a cunning trap for the advancing Arbiter and his Elite and Grunt allies, laying a large number of exploding weapons canisters to block a narrow stretch of the canyon and intending to explode them with Brute Shots as their enemies passed by, to create a tremendous explosion. Even this measure was unsuccessful as the Separatists forged towards a Brute encampment, which served as a weapons depot. Crashing down a waterfall, the Separatists charged the camp, which was holed in a large Forerunner facility. There were heavy defenses, including a pair of Wraith tanks, several Jackal Snipers, and a large number of Brutes. Soon enough, however, they were reinforced by two more Minor Elites arriving in drop pods. After securing the first half of the camp, the Arbiter and whatever surviving allies moved into the weapons cache, where the Brutes had aggregated a large number of Covenant and UNSC weapons alike, including M19 Rocket Launchers, M90 Assault Shotguns, Fuel Rod Guns, Brute Shots, and a variety of other weapons, demonstrating their religious heresy in their indifference against UNSC armaments.

As the Arbiter continued towards the second half of the encampment, the Loyalists became increasingly desperate, sending a group of reinforcements, including two Ghost vehicles from another Brute base, the Bastion of the Brutes. This was ultimately unsuccessful, and the Arbiter was able to advance to meet more friendly Elites, including Rtas 'Vadumee, who learned from the Arbiter of the Councilors' murder, and the treachery of the Brutes. Rtas 'Vadumee indicated that Tartarus was within the Control Room, and would soon be activating the Halos. However, the doors to the Control Room were nearly completely impenetrable, and would only be opened by the firing of the main cannon of a Scarab walker, and conveniently, one was nearby and under Brute control, docked with the Bastion of the Brutes.

While Rtas 'Vadumee advanced forward in a Wraith tank, the Arbiter and another Special Operations Elite took a Spectre, and together, the Elites battled through a swarm of Ghosts, three Wraiths, and a bombarding Phantom, narrowly clearing out the extensive Brute defenses on the exterior of their base and securing entrance into the Bastion of the Brutes, where the Arbiter found another Special Operations Elite and a pair of Hunters, all of whom were loyal to the Separatist cause. It appears a second Special Operations Elite was stationed with them, but was killed. Meanwhile, Rtas 'Vadumee said that he would briefly watch the Arbiter's back, and would prevent any Brute reinforcements from entering in behind them while they cleared out the stronghold. Later, he announced that he would retake the ex-Separatist battlecruiser that was hanging in the distance.

Some of the most tenacious Loyalist resistance was stationed in the indoor Forerunner structure taken by the Brutes as the "Bastion of the Brutes", however. There were two plasma turrets, and a large number of heavily-armed Brutes, with a disproportionate number of Brute Captains among them: sufficient firepower to even possibly down the powerful Hunter warriors that were fighting alongside the Arbiter. As the Arbiter and his allies continued through the base, passing through an outdoor bridge where they were beset by a Drone swarm and even a Phantom dropship, they came across a two-tiered Brute-held prison where the Brutes were holding inside forcefield generators a pair of Hunters and a pair of Councilor Elites. The Arbiter freed them by destroying the generators, and the reinforced Separatists were forced to defend the prison against another wave of Brute reinforcements before advancing to the last portion of the base: an external and outdoor docking platform where a Scarab walker was docked.

The Arbiter, his Hunters, and his Elites were able to kill the Brute Captains guarding the platform, freeing the two Marines (Marcus Banks and Pete Stacker) that were pinned down in the corner. However, Johnson still had command of the Scarab, and aimed its main cannon at the Arbiter. However, the standoff didn't culminate in a one-sided firefight: Johnson offered a deal. It was in the interest of both the UNSC and the Separatists to prevent Tartarus from using the Index to activate the Halos, so Johnson offered to blow open the locked doors of the Control Room with the Scarab's cannon while the Arbiter escorted him during the process, and then together, they would enter the Control Room and do whatever was necessary to prevent the firing of Installation 05.

Two Separatist Banshees landed on the platform, believed to have been sent by the recaptured nearby CCS-class battlecruiser, and both pilots offered their fighters to the Arbiter in his mission to escort the Scarab.

However, the short canyon and beachhead between the recaptured Bastion of the Brutes and the Control Room was heavily re-fortified by the Loyalists. No less than five Wraith tanks and two Spectres were stationed there to prevent the Scarab's passage, and four plasma turrets were mounted on the cliffs. However, the almost impervious armor plating of the Scarab was invulnerable to the plasma mortars of the Wraiths and the plasma cannons of the Spectres and the plasma turrets. Not only did the plasma munitions of the Loyalist vehicles do no noticeable damage to the Scarab, the Scarab was so powerful that it did not even have to open fire on it, and it could merely trample the vehicles underfoot with its four hulking legs. After those measures failed, the Loyalists deployed seven or eight Banshee fliers in an attempt to kill the Arbiter, who himself still mounted a Banshee. These efforts failed again, and the Loyalist Banshees did not even attempt to destroy the Scarab, for its armor was just too powerful.

Control Room
Shortly afterwards, the Scarab arrived before the Control Room, and blasted the front door open and burnt part of the frontal hemisphere of the building in three bolts from its massive main cannon. The Arbiter then unmounted, fought his way through one room with large numbers of Brute Captains and Brutes Honor Guards who had been ordered to prevent the Arbiter from disturbing Tartarus while he activated the Halos, or his "Holy Work". The Brutes appeared to be of increasing desperation, even commonly wielding UNSC-manufactured M90 shotguns, usually held as trophies. Despite reinforcements, the highly-ranked Brutes were unable to hold the room, and the Arbiter continued down an arched corridor before confronting Tartarus in the control room.

Tartarus had been trying to force his prisoner, Miranda Keyes, to shove the Sacred Icon into its receptacle on a holographic control panel in the massive, spherically-shaped central control chamber of the Control Room. Keyes, even under great pain, refused to do so, angering the brute chieftain. When the Arbiter arrived, he demanded that Tartarus put her down, and attempted to reason with Tartarus, urging him that the Prophets were indeed wrong, and activating the Halos would not commence the "Great Journey", but merely extinguish all sentient life in the galaxy. Near the end, the Arbiter even asked 343 Guilty Spark, who himself was a prisoner of Tartarus. When the Monitor attempted to respond, Tartarus snarled in frustration, and attempted to damage 343 Guilty Spark, when Johnson arrived, aiming a Particle Beam Rifle at Tartarus' head and threatening to kill him if he did not release the Monitor. The Arbiter then continued, asking 343 Guilty Spark again if he was right. The Moniter confirmed the Arbiters theory. Tartarus lost all patience, throwing the hard shell of the Monitor at Johnson, knocking him out for a moment, then clutching the Sacred Icon and forced Miranda Keyes to put it into its receptacle, beginning the activation of Installation 05. Behind their platform, a massive Forerunner multitiered construct began to open up: a three-storied structure, which at its center, boasted a brilliant gravitic column which was charging the ring to fire.

Miranda jumped out of the way of the imminent firefight as the Arbiter, the conscious Johnson, and a small cluster of recently-arrived Zealots and Councilors, charged at Tartarus and his guard of four Brute Captains. Almost immediately, the four captains were slain with little Separatist casualties, and Tartarus was forced back to the recently unveiled three-story structure. When the Arbiter and his allied Zealots and Councilors pursued, they found to their dismay that Tartarus was protected by a nearly impenetrable energy shield. While the Zealots and Councilors brazenly drew their Energy Swords and charged, Tartarus stood at dramatic repose, allowing them several swipes and the sudden knowledge that they could not lower his shields, before drawing his massive Gravity Hammer, the Fist of Rukt, and sending them flying to their deaths with single pounds.

Meanwhile, further reinforcements arrived: a continual stream of Special Operations Elites were joining into the fray, with the occasional Zealot and Councilor, mostly armed with Energy Swords, Carbines, or dual-wielded Needlers or Plasma Rifles. While the swords, Carbines, Needlers, plasma rifles, and even shotguns, plasma grenades, or overcharged plasma pistols were all ineffective, Johnson found that with his beam rifle, he could lower Tartarus' shields for a brief amount of time with three successive bursts from his rifle. While the Arbiter's allied Elites were oblivious to this, continually firing with their ineffective firearms even while Tartarus' shields were up and meeting a bloody death at the hands of the gravity hammer while all the while, 343 Guilty Spark announced that the installation was priming to fire, the Arbiter soon developed a tactic. He often would wait for Johnson to lower Tartarus' shields with his beam rifle shots, and then rush in and attack Tartarus while his shields were down.

However, soon after this new tactic was developed, it came apparent that the Separatists were not the only ones that brought reinforcements into the fight, and waves of Brute Captains regularly joined the fray in groups of three to five, clashing with the Arbiter's own Elite reinforcements, although oftentimes, the Elites were superior to Tartarus' Brute reinforcements.

In the end, after a long, protracted fight, the Arbiter was able to fire a finishing blow to Tartarus while his shields were downed, killing Tartarus, Chieftain of the Brutes.

Miranda Keyes immediately leapt to action after Tartarus died, snatching the Index triumphantly from the control panel. Despite the fact that Installation 05 was primed to fire, because of Miranda's quick actions, the removal of the Index only triggered a partial firing, one that was inconsequential and led to the loss of no life whatsoever.

However, 343 Guilty Spark warned that their quest to prevent the Halos from activating was not over: because of the partial activation of Installation 05, the other six remaining installations were set onto standby mode, and were ready to fire upon command from a central Forerunner installation: the Ark, one of the portals to which was located near Voi, Africa of the planet Earth.

Orbital Battle
While ground battles raged over the contested lands of High Charity and Installation 05, the Covenant fleets, divided, had not been idle or inoperative. During the hours which the Loyalists and the Separatists warred for the districts of High Charity, the Covenant fleet had splintered within itself, and its warships were destroying each other systematically over the planetoid as Brute-controlled warships raged against Elite-controlled ones. However, after the Prophet of Truth's departure in the Forerunner Ship, the fighting cooled as many ships fell silent, wondering what loyalties to assume in light of Truth's sudden abandonment and Tartarus's death, although a small number of starships continued fighting.

Despite the isolated Separatist ground victory on Installation 05, there was a much greater threat: the Flood. Having assumed dominance over the whole of High Charity and certain locations on Installation 05, they tried boldly expanding into space, attempting to take over Covenant warships. The ambitious Major Domo Elite Voro 'Mantakree assumed command of the Reverence-class Cruiser Incorruptible, and audaciously sent a fleetwide dispatch to the idling Covenant fleet amassed over High Charity: the Flood were lifting off from Installation 05 in DX-class "Spirit" dropships and Banshees and were attempting to attack and take control of Covenant warships to spread throughout the galaxy. Surprisingly, even divided political opinions were united after the transmission, and four Covenant Destroyers, including the Rapturous Arc, that were about to be consumed by the Flood were burned and destroyed to prevent the parasite from capturing the warships.

Shortly afterward, however, the fleets splintered without a common foe. The Alpha Jiralhanae Gargantum attempted to coordinate a Loyalist uprising against the Elites, and chased with four Covenant Frigates after 'Mantakree. Using deft tactics and maneuvering out the Separatist carrier Lawgiver, the Incorruptible destroyed the Brute-controlled frigate Tenebrous, although the three remaining frigates, including Gargantum's personal frigate, the Twilight Compunction, continued pursuing him. Soon afterward, the entire Covenant fleet began turning on itself, following Gargantum's example. The UNSC Dusk, one of the five UNSC ships originally sent to tail Regret's Assault Carrier, witnessed the massive encounter as Covenant ships turned upon one another and destroyed themselves in a civil war.

However, the Incorruptible did not continue in the orbital battle, as a revered Elite fleet commander, Imperial Admiral Xytan 'Jar Wattinree, urged all Elites to regroup over the outpost world Joyous Exaltation of the Salia System. 'Mantakree obediently left the battle, entering Slipspace towards Joyous Exaltation. During the pursuit, UNSC SPARTAN-II Blue Team dropped in the midst of the chase as the Incorruptible prepared to leave the system, in their captured Covenant Destroyer, the Bloodied Spirit. Gargantum was incensed that heretic Demons had seized a Covenant warship, and diverted one of the three pursuit frigates from the Incorruptible to the Bloodied Spirit. The frigate managed to lower the UNSC-controlled destroyer's shields before the SPARTANs jumped to Slipspace for the Zeta Doradus System.

It is heavily implied in Halo 3, that the Covenant Separatists defeated the Brute Fleet and subsequently held High Charity in quarantine. However, this largely failed, due to the Gravemind sending a single ship, controlled by the Flood, to Earth, in the hopes of infecting it and weakening the Elite ships in orbit around the Flood Hive. This was successful and the Gravemind was able to leave Installation 05's space and find the Ark.

Conclusion
The Battle of Installation 05 was an extremely costly battle with significant political-military consequences for the Covenant and remarkable ramifications for all sentient life in the galaxy. Hundreds or thousands of Covenant forces were slain in SPARTAN-117's quest to kill the Prophet of Regret, the race to acquire the Index from the Control Room, and the remarkable ground and orbital battles that took place on Installation 05, High Charity, and the Covenant fleets hovering above the planetoid because of the Covenant Civil War. The Covenant was fractured, with the Elites rallying the Covenant Separatists against the Prophet-supported Brutes, who controlled the Covenant Loyalists against the Elites and their allies.

The Covenant ruling system was destabilized, with the death of the Prophet of Regret on Installation 05 at the hands of SPARTAN-117 and the death of the Prophet of Mercy on High Charity at the hands of the Flood. The Prophet of Truth held the ultimate power now, with several Minor Prophets, completely re-shifting the political dynamics of the Covenant. The Brutes now held reign over the majority of the Covenant military, bringing their innate tenaciousness and ferocity to the front lines quite unlike the Elites had ever done. The Brutes also assumed more lower-level Covenant military authority, now replacing the Elites as the leaders of field squads and teams. The Brutes also introduced a unique set of bloodthirsty weaponry into the Covenant's field arsenals. The Covenant fleet was believed to lose quite a bit of its technical proficiency without the innate technical knowledge of the Elites.

Sentinel defenses were completely trampled over, particularly in the Quarantine Zone, where within hours, the Flood had managed to infiltrate the well-defended Sentinel Wall and seize control of large tracts of the Quarantine Zone, even grounding an airborne Sentinel Constructor Factory ship. The Flood also permeated the Library and the surrounding grounds, eliminating almost all Sentinels from the skies, leaving only scattered Enforcers to do battle with them. The Flood also controlled UNSC and Covenant vehicles alike, reinforcing their considerable ranks with M808B Scorpion Tanks, M12 Warthog LRVs, Wraith tanks, and Ghost vehicles. Flood losses were remarkably high because of the Arbiter's actions in the Quarantine Zone and SPARTAN-117's actions on High Charity. However, it was inconsequential: the Flood managed to terraform and transform High Charity into another of their "wretched hives", scoring a notable victory on High Charity, capturing the Covenant's mobile home planetoid.

UNSC losses were remarkably lower because of the small number of forces they brought into the theater of operations, almost solely the crew and soldiers of the UNSC In Amber Clad. Hundreds of Marines and Orbital Drop Shock Troopers, however, were lost in UNSC ground operations: the assassination of Regret and the storming on the Quarantine Zone, and a large number were infected by the Flood and made continual appearances as combat forms in the Sentinel Wall, Quarantine Zone, and Flood-infested High Charity. The crewmen of the In Amber Clad were presumably killed and reanimated by the Flood as well, bringing UNSC casualty rates possibly into the thousands, although the UNSC suffered by far the least casualties amongst the four warring factions in the Battle of Installation 05.

"Master Chief? Mind telling me what you're doing on that ship?"

- Fleet Admiral Hood

"Sir. Finishing this fight."

- SPARTAN-117

In the end, the fates of the Covenant fleets over High Charity is unknown, although at least one Covenant vessel, the Incorruptible, escaped. 'Matrankee was commended for his actions against the Flood on Installation 05, and was promoted to Fleet Master. The Flood continued to attempt to escape High Charity in Covenant starships, and a Covenant Separatist fleet led by Rtas 'Vadum on the Shadow of Intent held the line against the Flood. However, the Flood managed to infest at least one Elite-controlled ship, a CCS-class Battlecruiser, and made a Slipspace jump to Earth to attempt to infest the human homeworld. The Elite fleet in orbit over High Charity followed the Flood-controlled cruiser, and when the Flood ship crash-landed on Earth, Rtas 'Vadum and his forces aided the UNSC Home Fleet in destroying the Flood vessel and terminating the Flood spread across the planet. However, prior to this, High Charity had already left its orbit around Installation 05, and according to a scrambled distress signal from Cortana, was already on its way to Earth to enter the Portal. It was indicated though that all of the other Flood controlled ships were destroyed though: upon landing on Earth an Elite informed the Arbiter that the Elite's fleet had taken care of all of the Flood controlled ships, except for that one which had managed to break through and jump to Earth. It can be inferred that the Flood controlled ships were ultimately all destroyed except the one that jumped to Earth and High Charity which was later destroyed by the Master Chief in the Battle of Installation 00. Cortana was left to the clutches of the Gravemind. It was later shown that she answered a few questions to buy herself some time and used the opportunity to help find a way to destroy the Flood. She would later be rescued by the Master Chief who would then destroy High Charity during the Raid on High Charity.

SPARTAN-117 was aboard Truth's Forerunner Dreadnought, which managed to reach Earth unharmed and landed in Africa, near the Portal to the Ark, about two weeks after its departure from High Charity. The UNSC Dusk eventually withdrew to rendezvous with Battlegroup Stalingrad shortly outside of the Onyx System, and the UNSC In Amber Clad remained crashed into one of the towers of High Charity.

In many ways, the battle was the true turning point in the war and in the long term would break the back of the Covenant. The Elites eventually allied themselves with the humans bolstering their fleets and taking the military strategy mind away from the Covenant.