Onyx Conflict

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

Space
The Beatrice arrives, is engaged by Sentinels, and crash lands on Onyx. Kelly-087 and Halsey manage to survive. Later, the Bloodied Spirit arrives, is engaged by Sentinels, forcing Fred-104, Will-043, and Linda-058 to bail in a Spirit.

Voro Nar 'Mantakree, a newly appointed Covenant Zealot Elite, arrives at the scene in order to purge Onyx of UNSC forces and harvest the Forerunner technology believed to be there. His task force makes contact with the Sentinels, who initiate fire on the Far Sight Lost. He orders the Absolution to perform a precision slipspace jump to the northern polar areas of Onyx for scouting purposes, and the Sentinels use this to jump through slipspace and then destroy the Absolution as it exited slipspace. Voro orders the fleet to Zone 67 and discovers the Forerunner city and homes in on the human’s location.

The UNSC Dusk, a Prowler, arrives at Onyx via slipspace in the wake of the Bloodied Spirit after Voro engages the Sentinels. Shortly thereafter, Admiral Patterson arrives with a battle group intending to catch the Covenant off guard. The battle group finishes off several Covenant destroyers using  Archer missiles and nukes. A single destroyer survives, and fires at the UNSC  Stalingrad, the flagship of the battle group where Admiral Patterson was commanding from. The battle group launches MAC rounds to finish the ship and the UNSC  Glasgow Kiss puts itself between the Stalingrad and the plasma fire and some of the crew bails out.

The Covenant destroyer takes multiple hits and flees to the other side of Onyx, leading the UNSC battle group into a trap of twenty Covenant warships. The UNSC ships manage to take out several destroyers, but the Covenant launches a massive volley of plasma. The UNSC ships accelerate into the attack in hopes of emerging too close for a second volley. Five ships survive the volley, of which one, the UNSC  Iwo Jima, crashes into several enemy ships, taking two down and damaging six others in the resulting explosion. The other four manage to flee to the other side of Onyx. The Sentinels choose this time to attack the Covenant fleet, destroying an additional three destroyers and buying the UNSC ships time to retreat and regroup. The Covenant ships attempt to retreat from the gravity of Onyx, using two ships as decoys while the rest pull back.

The UNSC prepare to engage the Covenant ships again. The Dusk lays a [[HORNET Mines | HORTNET] nuclear minefield on either side of Onyx’s moon. The UNSC ships then fire from behind the moon at the Covenant ships; three Covenant ships are hit, but remain undamaged. As the Covenant ships enter the mine fields, the UNSC detonate the HORTNET mines and destroy twelve of the sixteen Covenant ships. Admiral Patterson maneuvers his four ships in and finish off two of the wounded Covenant ships immediately. The other two Covenant ships travel around the moon, and as they come back to face the remaining UNSC ships, a Covenant armada of thirty-two ships jumps from slipspace and utterly destroy Admiral Patterson’s remaining ships.

Ground
The battle began when the Sentinels of Onyx engaged the Spartan-IIIs and other personnel on Onyx during the Top Honors exercise of Gamma Class. Team Gladius went MIA, considered KIA, almost immediately. Team Katana was captured. Team Saber linked with Kurt-051,  Tom-B292,  Lucy-B091, and  Chief Mendez to form a resistance. Kelly-087 and Dr Halsey crash land on Onyx later, and link up with Team Saber and Kurt-051. The Sentinels they fight are different from those seen on the Halos. They are much stronger, and several physical differences. Team Saber and company try to fight them, but the struggle is tough.

Fred-104, Will-043, and Linda-058, having recently captured the Bloodied Spirit, arrive at Onyx in response to a distress call from Halsey requesting Spartans. They immediately come under attack from Sentinels and have to bail out in a Spirit. They link up with Kurt-051 and his team and plan an attack on Zone 67. They fly into the crater in a Spirit, and then find a Forerunner city.

A firefight between Covenant forces and Kurt-051’s forces in the Forerunner city ensues. Kurt-051, Fred-104, Linda-058, and several Spartan-IIIs try to hold the Covenant back while Halsey tries to configure a teleportation grid for them. Kelly-087 and Mendez are with Halsey. Dante-G188 is killed while rescuing Fred-104 by plasma and Needler fire. Halsey gets the teleportation grid working, and they all teleport to the Sentinel Production Facility near the northern pole in Onyx. Halsey sends them to destroy three key structures, which would bring the entire production to a halt. Using the teleportation grid, they go to the three structures and trick Sentinels into firing on them on a line with the structures. Having destroyed the structures, they teleport back.

Kurt-051 and his team arrive at Team Katana’s holding area and find them in some sort of cryo-slipspace containment cells. There are eight such containers, five of which contain Spartan-IIIs. They travel to the Core Room Antechamber, where they prepare to hold off a Covenant invasion force from a small tower. The Covenant have three Hunter pairs, Elites from the E’Toro, R’Lan, and N’Nono warrior crèches, and plenty of other troops. First, they sent two hundred Grunts to distract Kurt-051 and company while Elites set up stationary shield generators. There were three groups of thirty Elites and one Hunter pair behind each shield. The Elites form a line and advance behind Jackal shields. Kurt-051’s group uses grenades and  snipers to counter. When the Elites and Hunters approach the stairs, Kelly-087 detonates LOTUS mines placed on the first step, killing several Elites and dazing two Hunters. Kurt-051 kills one Hunter, but the other manages to duck behind its shield. Kelly-087 engages three sword-wielding Elites, killing all three, but is flanked by two Hunters. Holly-G003 sacrifices herself to save Kelly. Kurt rushes forward and a Hunter slashes him with its shield. Linda-058 puts a round into the Hunters midsection, and then Will-043 engages them both in hand-to-hand combat. He kills one, but the other shoots him. Fred-104 kills the second with a well placed Jackhammer missile.

The Covenant forces pull back. Hundreds of Elites, Banshees, and Grunts prepare for the main assault. Kurt-051 orders all other personnel through the core and into a Micro Dyson Sphere. Kurt-051 stays behind, and after the rift closes, the Covenant approach. Voro approaches, intending to kill Kurt-051 and then reopen the rift, when Kurt-051 detonates the two FENRIS nukes, killing himself, Voro, and the entire Covenant force in the Core Room Antechamber.