Battle of the Quarantine Zone

"We shall cut into the heart of this infestation, retrieve the Icon, and burn any Flood that stand in our way!"

- Rtas 'Vadumee

The Battle of the Quarantine Zone was a battle which took place on Installation 05 for a span of nearly 100,000 years. When the ring was later discovered in 2552, the Covenant and UNSC fought through the Quarantine Zone in search of the Activation Index, known to the Covenant as the Sacred Icon. Both parties had to battle their way through legions of Flood and Forerunner machines designed to halt the parasitic outbreak.

Background
Not much is known of how the battle of the Quarantine Zone began, as it is rooted in ancient history. The battle began after an unknown event, approximately 3,000 years after the activation of the Halo Array, when the Flood under containment on Installation 05 were released. Under normal circumstances Sentinel guards would have been able to keep the parasite under control. Unfortunately, the Flood had access to hosts, and were able to hold off the constructs.

After building enough biomass, a local proto-Gravemind reached critical mass, allowing the formation of a sentient, highly aware form of flood stage known as the Gravemind. Now coordinated, the Flood posed a serious threat. The battle soon spiraled out of control, and Sentinel manufacturing facilities constructed more powerful constructs, such as Sentinel Majors and Enforcers. An enormous wall had been built around the Installation's Library, which was housing the Gravemind. The area within the boundaries of the wall were starved of heat and light in order to inhibit Flood growth, thus establishing the Quarantine Zone.

Over the centuries, the Gravemind's reach spread throughout the installation. The Monitor of the installation, 2401 Penitent Tangent was captured by the Gravemind, giving him access to the teleportation grid, and causing the structures on the Installation to fall into disrepair.

UNSC Incursion
"Proceed to the objective, we'll hold out as long as we can!"

- Gunnery Sergeant Marcus Stacker, as the flood overwhelm UNSC forces inside the Sentinel Wall.

Shortly after arriving in the Coelest system in pursuit of the Solemn Penance, Commander Miranda Keyes of the UNSC In Amber Clad demanded the AI Cortana provide her with all information from the installation her father had discovered a month prior. Keyes was able to locate Installation 05's Library, and set out to reach it and secure it's Activation Index before the Covenant could do so. Marine forces lead by Sergeant Major Avery Johnson were ordered to extract from their positions on the ring's surface and rendezvous with the In Amber Clad at the Library.

Upon arriving at the Sentinel Wall surrounding the Library and the Containment Shield it projected, the In Amber Clad deployed a platoon-sized force of Marines to the wall led by Gunnery Sergeant Marcus Stacker and Staff Sergeant Banks. The Marines moved through the outer wall with ease, unmolested by local Sentinel defenses - likely due to being recognized by the automated guardians as Reclaimers.

As the Marines moved through the inner wall, the outer wall became besieged by Jiralhanae-led Covenant forces deployed from the recently arrived High Charity. Eventually, the Arbiter Thel 'Vadamee was able to deactivate the Containment Shield, and the inner wall quickly became overrun with Flood from the nearby Quarantine Zone.

Spread throughout the wall in small fireteams and completely unaware of the nature of enemy they were facing, most of the platoon was quickly assimilated by the parasite, proceeding to take up arms against their former comrades. Additionally, the local Sentinel forces became hostile to the surviving Marines, likely due to the immediate presence of the Flood. With his forces decimated, but the Containment Shield now disabled, Stacker radioed In Amber Clad suggesting Keyes proceed straight to the Library while his troops attempted to hold their position. A short time later, Stacker made contact with Keyes once again, confirming their engagement with non-Covenant hostile lifeforms, while Banks and other Marine survivors could be heard staging a desperate defense.

The In Amber Clad swiftly took advantage of the lowered Containment Shield, deploying it's full strength to the icy plains of the Quarantine Zone as battle raged between Flood and Sentinel forces. Multiple M808 Scorpions and M12 Warthogs were deployed via dropship, and the UNSC forces pushed towards the Library. UNSC superiority would be short-lived however, as the Flood's acquisition of vehicles brought by the In Amber Clad and arriving Covenant forces swung the battle in their favor. With the subsequent destruction of a Sentinel manufacturing facility reinforcing the Quarantine Zone, the flood presence quickly became overwhelming.

Eventually reaching a large facility with multiple anti-gravity gondolas designed to take them to the Library, Keyes' forces staged a final stand at the facility exterior, utilizing a Scorpion and multiple stationary M247 machine gun turrets. The position was swiftly overrun as Johnson and Keyes led a small squad of Marines into the facility. They boarded the Gondola moments before Covenant Special Operations forces arrived, who followed in close pursuit on a gondola of their own.

As Johnson and Keyes entered the Library to secure the Index, the Marine squad defending the facility entrance was killed by Flood Pod Infector forms. The pair thus had no warning as a cloaked Thel 'Vadamee ambushed them, and arriving Jiralhanae forces led by the Chieftain Tartarus subsequently captured the index, taking the unconscious Johnson and Keyes as prisoners.

With the majority of the ship's Marine complement killed in action, the In Amber Clad was eventually overrun by the surging Flood presence, and it's entire crew presumably killed.

Covenant intervention
Thel 'Vadamee, the Arbiter of the Covenant, was personally ordered by the Prophets to journey to the surface of the ring to retrieve the Index (or the Sacred Icon as the Covenant call it), some time after the UNSC began their operation. Dropped directly into the outer wall by a Phantom transport, the Arbiter fought mostly alone, only aided by a small number of the original landing party (several Unggoy and Kig-yar), through numerous Forerunner constructs to reach the control center for the containment shields. By lowering these shields, the Covenant soldiers learned that human Marines had made it through the wall first, only to be swiftly infected by the Flood. By lowering the Containment shields, the Covenant allowed more free movement for the Flood. More Covenant warriors soon entered the Quarantine Zone along with their own vehicular support, unfortunately exacerbating the Flood outbreak.

This breach of containment led to the rapid growth in the Flood's numbers as they assimilated both humans from the and Covenant warriors. With these new hosts, the Flood gained access to more sophisticated equipment, weapons and combat vehicles, magnifying the danger the outbreak presented immeasurably. The Flood showed a bit of a tactical genius by destroying one of the Forerunner Sentinel manufacturing plants, bringing it crashing down on the surface and stopping the production of Sentinels and Enforcers. This meant that while the Flood might not have to fight as many Forerunner machines, human and Covenant forces would possibly be able to get to the Index easier.

Despite this new and surprising defense, Covenant and human forces were able to battle their way through the legions of Flood and Sentinel constructs. Elements of both parties eventually reached the gondola entrance points to the Library of Delta Halo. Commander Miranda Keyes, Sgt. Johnson and a number of Marines entered the Library first. They were quickly followed by the Arbiter and a squad of Sangheili SpecOps troops. Rtas 'Vadumee stayed behind to defend the Gondola station.

Human forces had gained access to the Library first, but only by a matter of minutes. The Arbiter exited the Gondala while his fellow Sangheili warriors stayed aboard to guard it, as it was the only entrance/exit. Upon exploring the interior of the Library, it was clear that the humans had faced stiff opposition, all but two of their forces had died combating the Flood and Sentinels already within its walls.

The Arbiter found Miranda Keyes and Sergeant Johnson within the Index Chamber, having retrieved the Index seconds before his arrival. Sergeant Johnson was ready, armed with a Battle Rifle, along with Miranda Keyes who was reaching for the Index holding on to one of the Gravemind's tentacles. Miranda secured the Index and drew two SMGs. Johnson called for his marines, but received no answer and armed his weapon. The Arbiter proved his worth as a warrior once again, incapacitating both Johnson and Keyes in a matter of moments. The arrival of Tartarus and his hostile Jiralhanae forces within the Chamber, after making their way through the Sangheili forces guarding the Gondala, signified the beginning of the Great Schism. Tartarus briefly told the Arbiter how the Sangheili had been expelled from the Covenant under the orders of the High Prophet of Truth, and proceeded to attack the Arbiter, sending him plummeting to his doom deep within the Library, towards the Gravemind.

Conclusion
The battle itself was from a strategic stand point, a Covenant victory. They succeeded in not only obtaining the Index but captured all of the Marines that were not infected (the Covenant were well aware that to activate the rings a human hand was required). The Flood on the other hand, won a tactical victory, succeeding in not only escaping Installation 05 but gained the means to spread to other worlds through infesting all the nearby ships (i.e. In Amber Clad). The UNSC forces, on the other hand, failed to recover the Index and were almost completely killed or captured by the Covenant or infected by the Flood and the Forerunner constructs, without the leadership of 2401 Penitent Tangent could not stop the Flood from escaping the ring.

List of appearances

 * Halo 2
 * Halo: Broken Circle
 * Halo 2: Anniversary