Omega Halo

Omega Halo, originally known as Gyre 09, was one of the original twelve Halo installations built at the greater Ark, and the last to be destroyed.

Background
Unlike the six rings of the final Halo Array, Omega Halo was manufactured at the greater Ark instead of Installation 00. Like the other Halos built at the greater Ark, Omega Halo's main weapon was designed to fire directed pulses as opposed to the omnidirectional effects of the newer Halos. Omega Halo was the last 30,000 kilometer Halo to be built. By the last year of the Forerunner-Flood war, all but one of its counterparts had been destroyed either during the assault on the Capital world or by Flood/Precursor forces in the intervening years; Installation 07 had been severely damaged, reduced in size, and repurposed alongside the smaller, final Array. Omega Halo itself retreated from the fall of the Capital through a slipspace portal, the only one of the two Halos that tried to make the transit and survived.

Siege of the greater Ark
As the ecumene's territory was driven back toward the heart of Forerunner civilization, the Capital world fell to the Flood. As such, the surviving members of the New Council moved the seat of government to the greater Ark, outside the galaxy. The tattered remnants of the Forerunner military gathered at the Ark in preparation for a final stand; Omega Halo was positioned near the Ark in case its use became necessary. Oriented toward the satellite galaxy of Path Kethona, the Halo would fire a directed pulse designed to purge Path Kethona of all life, Precursor artifacts or Flood. Specimens from the Lifeworkers' Conservation Measure were moved to the Ark; many humans were soon moved to Omega Halo to prevent excessive crowding on the larger installation.

Shortly after the IsoDidact, the Librarian, and the Ur-Didact arrived at the staging ground, an enormous Flood fleet emerged from slipspace only a few million kilometers away. Led by the rogue ancilla Mendicant Bias, the Flood-controlled fleet was merely a screen for a swarm of Precursor star roads, which could physically crush entire planets.

The Ur-Didact's betrayal
As the battle raged, the Ur-Didact took his personal ship to the surface of Omega Halo. There, he used a Composer to convert the relocated human population, (numbering in the hundreds of thousands), into digital forms. He then returned to the Prometheans' primary shield world, Requiem, where he implanted the essences into Promethean Knights. The Librarian, a former companion of the Ur-Didact; and Chakas, a monitor; were unable to stop this quasi-genocide; however they managed to recover a relative handful of live specimens and DNA samples, which were immediately transferred to the lesser Ark.

Activation and destruction
As the Ur-Didact fled to Requiem and the Librarian made for Installation 00, the IsoDidact, Bitterness-of-the-Vanquished, and the Examiner traveled to Omega Halo's control room. Knowing that Precursor neural physics were extremely vulnerable to Halo radiation, they hoped to clear an egress route among the vast tangle of star roads. Soon after the trio's arrival, Master Builder Faber entered the control center and vaingloriously insisted that he be the one to fire the installation's weapon. He managed to fire a single pulse toward Path Kethona, disintegrating multiple star roads and opening a path away from the Ark while sterilizing Path Kethona. Unfortunately, the Forerunners' position was quickly overrun and some of the remaining star roads converged on the Halo. Enormous tidal and kinetic stress rent the installation asunder; the vast degree of friction caused parts of the Halo to superheat and melt.

The floor of the control center gave way, causing Bitterness, the Examiner, and the Master Builder to plummet to their deaths. The IsoDidact was unable to grab a salient as he fell, though the monitor Chakas fortuitously arrived and carried him to the lesser Ark to coordinate the final stages of the Halo Array's activation. As the pair escaped, the star roads crushed Omega Halo and the greater Ark. With the loss of Omega Halo, the Forerunners were forced to resort to the smaller, more powerful secondary array of 10,000 kilometer-wide Halos; these rings would, in the coming weeks, destroy all life in the galaxy.

Production note
Omega Halo first appeared in the sixth terminal in Halo 4 ' s campaign. The events depicted in this terminal were later adapted and expanded (in a highly modified form) in Halo: Silentium. The terminal depicts Omega Halo in orbit around a gas giant with several nearby moons; there are no signs of the battle described in the novel. Another key difference is that the Librarian and a team of Lifeworkers are shown investigating the attack on the human population shortly after its occurrence; the Librarian confronts the Didact via a hologram and rebukes him for refusing to speak to her in person. In the book the Didact leaves as soon as the humans are composed, while the Librarian is focused on getting the remaining humans to the lesser Ark.

Fictionally, Halo 4 ' s terminals are depicted as transmissions from within the Domain, whereas Silentium is presented as legal testimony from several individuals who were present during the battle, most importantly the Librarian, contained within the memory banks of a Catalog and a monitor. The terminals have since been explained as abstractions of historical events on behalf of the Domain with the narrative of Silentium being treated as factual. The real-world explanation is that 343 Industries wished to tell the stories presented in the terminals within a short timeframe, leading to the compressed relation of the events in question.

List of appearances

 * Halo 4
 * Terminals
 * Halo: Cryptum
 * Halo: Silentium
 * Halo Mythos