Onyx Conflict

The Battle of Onyx was a very large and prolonged military engagement between the Forerunner Sentinels, United Nations Space Command and the Covenant Separatists.

Sentinel Activation
When Alpha Halo was destroyed, it emitted a signal that placed all other Forerunner installations in standby mode, including the Sentinels guarding the Shield World disguised as the planet of Onyx. On October 31, 2552, the first of these Sentinels to awaken suddenly began attacking UNSC forces on or near Onyx. Coincidentally, Gamma Company was participating in the Top Honors exercise at the time.

Almost immediately, Team Gladius and the orbiting were destroyed and Team Katana captured. The SPARTAN-III trainers, save for SCPO Mendez and Kurt-051 were all killed as well. Team Saber regrouped with Kurt-051, Tom-B292, Lucy-B091 and SCPO Mendez, although they had no means of summoning reinforcements from the rest of the UNSC. Mendez declared Bloody Arrow.

Dr. Catherine Elizabeth Halsey, Kelly-087 and AI Jerrod arrived aboard Beatrice. Attacking Sentinels forced the ship to crash land on the planet, although all three passengers survived to link up with Kurt-051's group. Halsey proceeded to convince the resident ONI AI, Endless Summer, to send a distress message to the UNSC using the Slipspace COM Launcher. In the signal Halsey requested the deployment of SPARTAN-II's to Onyx. The launcher was destroyed shortly after firing.

The message succeeded in reaching a besieged Earth and diverting Blue Team to Onyx. However, en route the message had been intercepted by the Covenant. The newly promoted Fleet Master Voro Nar 'Mantakree of the Second Fleet of Homogeneous Clarity was deployed to Onyx under orders to destroy all UNSC forces and recover any Forerunner artifacts.

Blue Team and the Covenant Arrive
Blue Team, composed of Will-043, Linda-058, and Fred-104, arrived at Onyx aboard the commandeered Bloodied Spirit, but were forced to make their way down to the surface in a Spirit when their ship was attacked by Sentinels. Linking up with Kurt-051's group they planned to attack Zone 67. Using the Spirit they flew into a crater and discovered a Forerunner city.

At the same time, 'Mantakree's forces formed around the Incorruptible and began nearing Onyx. The Far Sight Lost was sent ahead to scout the environs but was quickly engaged and destroyed by Sentinels. Another scout, Absolution, was ordered to perform a precision Slipspace jump to the northern polar areas of Onyx, but the Sentinels followed it through Slipspace and the Absolution was destroyed upon exiting Slipspace. However, sufficient information had been gathered and 'Mantakree ordered his ground troops, including Elites from the E’Toro, R’Lan and N’Nono warrior crèches, to converge on Zone 67.

Battlegroup Stalingrad
Shortly after 'Mantakree had engaged the Sentinels, the arrived by Slipspace from Earth. The Prowler provided advanced intelligence for Battlegroup Stalingrad that arrived shortly thereafter. Intending to catch the enemy off guard, the UNSC force homed in on a group of Covenant destroyers and destroyed all but one destroyer. The was sacrificed to preserve the  from plasma fire from the lone destroyer. Escape pods from the Glasgow Kiss were used to intercept three of the four lances of fire.

Despite taking multiple hits, the Covenant destroyer fled to the other side of Onyx, leading the UNSC force into a trap of twenty additional Covenant warships. Several more Covenant destroyers were eliminated, but the launch of a massive plasma volley forced the UNSC ships to accelerate into the attack and close the distance to forestall a second volley. Only five UNSC ships survived the charge, of which one, the, was destroyed when she detonated a nuclear weapon in her engine, destroying a further two Covenant warships and damaging six more in the ensuing explosion.

Defeated once more, the remaining Covenant ships withdrew again to the opposite side of the planet but were there attacked by Sentinels who used plasma capture to destroy yet another three destroyers. Realizing their peril, the Covenant ships began to withdraw from Onyx's gravity well. Two ships were used as a rearguard and one was destroyed. 16 ships escaped in all.

The intervention of the Sentinels allowed the UNSC ships time to regroup around Onyx's moon. There Dusk laid a minefield of 14 HORNETs, each rating at thirty-megatons with vacuum enhanced loads. The UNSC warships then opened fire from behind the moon, hitting some of the enemy but causing negligible damage, but drawing the Covenant's attention. As the Covenant closed to engage and entered the field the HORNETs were detonated, destroying all but four of the remaining Covenant warships. Two of these were immediately set upon by the UNSC and destroyed. The remaining two whipped around the moon and as battle was about to be joined again, a Covenant Fleet of 32 ships arrived from Slipspace. Battlegroup Stalingrad was completely destroyed, except for Dusk, in the one-sided engagement that followed.

Retreat to the Shield World
While the UNSC and Covenant Fleets traded space-borne crossfire whilst in orbit, in the Forerunner city Kurt-051's group of survivors was engaged by Covenant troops led personally by Voro Nar 'Mantakree. The Spartans (both II's and III's) held off the enemy advance while Halsey, aided by Kelly-087 and Mendez, configured Onyx's teleportation grid, their means of escape. Dante-G188 was killed rescuing Fred-104 from plasma and Needler fire. Once the teleportation grid was functioning, the humans moved to the Sentinel Production Facility near the north pole in the aim of destroying it. At the advice of AI Endless Summer, this would save Battlegroup Stalingrad. Halsey identified three key structures in the facility and they were destroyed by tricking Sentinels into firing on them. Moving on, Kurt-051's group came upon Team Katana trapped in some sort of Slipspace stasis pods. Unable to free the prisoners, the humans were forced to bring the sarcophagi with them as they traveled to the Core Room Antechamber where they prepared a stand against pursuing Covenant troops.

While two legions of the cannon-fodder Grunts attacked Lieutenant Commander Kurt-051 and his forces atop the stepped structure, the remainder of the attackers setup stationary shield generators and placed three groups of thirty Elites and one Hunter pair behind each shield. From this jump-off point, the Elites formed a wall using shields taken from Jackals and began to advance through grenade and sniper fire. When the Covenant reached the first step, redeployed Lotus mines killed several Elites and dazed Hunters. One Hunter was dispatched by Kurt-051 before they could recover. Kelly-087 engaged and killed three sword-wielding Elites and was then flanked by two more Hunters but was saved by Holly-G003, who was killed in the effort.

The Spartans piled onto the two Hunters. Kurt-051 was wounded. Will-043 killed one Hunter, that had been shot by Linda-058, in hand-to-hand combat but was in turn shot and killed by the second. The last Hunter was killed by Fred-104 with a Jackhammer missile.

However, the main Covenant assault with hundreds of Elites, Banshees and Grunts, was yet to come. Realizing it was futile for his diminished force to resist further, Kurt-051 ordered the survivors into Shield World while opting to remain behind to prevent the Covenant from reopening the portal. With 'Mantakree approaching to finish off the wounded Spartan personally, Kurt-051 detonated two FENRIS warheads, killing himself and the entire enemy force in the Antechamber as well as triggering the Sentinels of Onyx to "erupt." With the portal closed, his comrades who had escaped into Shield World were trapped, but unharmed. His last words were: "Die? Don't you know? Spartans never die."

Destruction of Onyx
With the Shield World closed and gated by Kurt-051, Onyx 'disintegrated' into its trillions of component Sentinels. The Covenant Fleet, so recently victorious against the Humans, were finally obliterated by the swarm of vigilant constructs. Only the managed to escape alive and intact. It is not known whether the data the carried  ever reached Earth.

Space

 * Human
 * Admiral Carl "Buster" Patterson
 * Commander Richard Lash
 * Lieutenant Commander Julian Waters
 * Lieutenant Commander Xaing Cho
 * Lieutenant Bethany Durruno
 * Lieutenant Joe Yang
 * Lieutenant Junior Grade Fred SPARTAN-104
 * Petty Officer Second Class Will SPARTAN-043
 * Petty Officer Second Class Linda SPARTAN-058
 * Covenant Separatists
 * Voro Nar 'Mantakree
 * Uruo 'Losonaee
 * Zasses 'Jeqkogoee
 * Y'gar 'Pewtrunoee
 * Ship Master Qunu

Ground

 * Human
 * Lieutenant Commander Ambrose / Kurt SPARTAN-051
 * Lieutenant Junior Grade Fred SPARTAN-104
 * Senior Chief Petty Officer Franklin Mendez
 * Petty Officer Second Class Will SPARTAN-043
 * Petty Officer Second Class Linda SPARTAN-058
 * Petty Officer Second Class Kelly SPARTAN-087
 * Petty Officer Second Class Lucy SPARTAN-B091
 * Petty Officer Second Class Tom SPARTAN-B292
 * Petty Officer Second Class Holly SPARTAN-G003
 * Private Ash SPARTAN-G099
 * Petty Officer Second Class Dante SPARTAN-G188
 * Petty Officer Second Class Olivia SPARTAN-G???
 * Petty Officer Second Class Mark SPARTAN-G???
 * Dr. Catherine Elizabeth Halsey
 * Endless Summer AI#4279
 * Jerrod "Micro AI"
 * Covenant Separatists
 * Voro Nar 'Mantakree
 * Paruto Xida Konna
 * Waruna Xida Yotno

UNSC

 * Battlegroup Stalingrad
 * , Carrier
 * , Destroyer
 * , Destroyer
 * , Destroyer
 * , Prowler
 * , Frigate
 * Beatrice, modified

Covenant Separatists

 * Incorruptible,
 * Sublime Transcendence, Covenant Supercarrier
 * Absolution, Covenant Destroyer
 * Bloodied Spirit, Covenant Destroyer
 * Far Sight Lost, Covenant Destroyer

Trivia

 * It is interesting to note that the Separatists are fighting Humans despite the Arbiter's alliance with the UNSC. This is likely due to the amount of time for a message to be received from near Installation 05. Which, although the Incorruptible was present during the Battle of Installation 05, a message would not have been sent at the time.
 * The SPARTANS trapped in shield world are listed as M.I.A. yet the UNSC Dusk knew they were trapped.