2552

2552 was the penultimate year in the Human-Covenant War, during which the Humans of the United Nations Space Command nearly saw utter defeat and extinction, though the tide turned, and with the help of the Sangheili, won the Human-Covenant War. The Covenant were at the peak of their power and reach in 2552, with major assaults on the Human Inner Colonies and an invasion followed by a prolonged engagement on their home planet, Earth. During the battle at Installation 04, the galaxy found its first large outbreak of the Flood threat in over a hundred thousand years. Over two months later, an even larger outbreak occurred at Installation 05.

The war finally drew to a close at Installation 00, known more commonly as the "Ark", with the Humans and Sangheili attempting to assassinate the Prophet of Truth, before he could activate the remaining Halo Installations. The alliance was successful in their mission against the Covenant.

January
January 8th
 * A team of ODST's (Including Kojo Agu and Taylor H. Miles) descend onto Ariel (a small science colony) in response to a distress call on the planet in Operation: FIRESIDE.

February

 * Insurrectionists on Harmony disable the planet's primary communications relay and steal two drydocked freighters.

April
April 22nd
 * Battle of the unidentified human colony: Noble Team member Thom-293 destroys a but kills himself in the process. Catherine-B320 loses her right arm.

May
May 10th
 * SPARTAN-B312 participates in a counter-insurgency operation on Mamore. The SPARTAN exhibits great skill as a YSS-1000 Sabre pilot, garnering the approval of Colonel Urban Holland and leading to the SPARTAN's assignment to Noble Team.

July
July 17th
 * Slipspace probes from the Archimedes encounter Covenant ships sent to attack Sigma Octanus IV.
 * The is tasked with patrolling the Sigma Octanus system.
 * The Battle of Sigma Octanus IV begins.

July 18th
 * The UNSC win a victory during the battle at Sigma Octanus IV. Commander Jacob Keyes of the Iroquois plays a critical role in this success, destroying multiple Covenant vessels with the eponymous "Keyes Loop". Keyes is subsequently promoted to Captain by Vice Admiral Michael Stanforth. Unknown to the UNSC, the Covenant place a tracker on the hull of the Iroquois. The importance of Reach to the UNSC is revealed to the Covenant when the Iroquois returns to that world.

July 23rd
 * 3 Charlie, a UNSC Army fireteam, is sent on patrol in Longhorn Valley on Reach. They receive orders to investigate a disturbance at the Visegrad Relay.

July 24th
 * Two months after the death of Thom-293, SPARTAN-B312 joins Noble Team as Noble Six.
 * SPARTAN Noble Team is sent by Colonel Urban Holland on a mission to investigate the disabled Visegrad Relay. Holland and the SPARTAN believe that the relay has been sabotaged by insurrectionists. Instead, Noble Team discovers the presence of a Covenant strike force. WINTER CONTINGENCY is declared on Reach.

July 26th
 * Sword Base, an Office of Naval Intelligence research facility, comes under attack by a Covenant corvette. UNSC Army forces, with the help of Noble Team, successfully repel the attack. The corvette is destroyed by orbital support.

August
Unknown date
 * After discovering Reach, the Covenant move on to glass the other planets in the system, including Tribute, resulting in the prolonged Battle of Tribute.
 * During the Battle of Tribute, SPARTAN-II Team Black is sent to Verge to destroy a Covenant Beacon supplying helium-3 to the ships laying siege on Tribute. The team successfully destroys the beacon.
 * After the mission on Verge, Fireteam Black is assigned to Operation: BLOWBACK, a covert mission in Covenant-occupied space. Their ship, as well as a Covenant carrier, crash-land on an unknown moon, igniting the Battle of Line Installation 1-4.

Early August (sometime from the 6th to the 12th)
 * The crashes in lunar orbit, a Slipspace Anomaly knocking out communications within the Solar System for seven seconds.

August 12th
 * John-117 and Corporal Harland are debriefed by ONI at Camp Hathcock, Reach, on the events on Côte d'Azur during the Battle of Sigma Octanus IV.
 * Battle of Viery: UNSC forces assault an amassing Covenant invasion force in the Viery Territory on Reach. A cloaked Covenant supercarrier (the Long Night of Solace) that spearheaded the Covenant invasion is revealed.

August 13th
 * 60% of the remainder of the UNSC fleet is recalled to Reach, with the first battle group arriving in 48 hours.

August 14th
 * Operation: UPPERCUT is initiated, as Noble Team retakes the Sabre Program Launch/Research Range and joins the battle in orbit, eventually capturing the Covenant corvette Ardent Prayer and using it to deliver the 's Shaw-Fujikawa Translight Engine, used as a makeshift bomb, to the Long Night of Solace . The Solace is destroyed at the cost of Jorge-052, who sacrifices himself to detonate the drive manually. Moments after the carrier's destruction, a massive Covenant fleet enters in-system.

August 18th
 * Siege of New Alexandria begins as the Covenant lay siege to the city of New Alexandria.

August 23rd
 * Noble Six participates in the Battle of New Alexandria on Reach. Six rescues civilians by helping them escape. Noble Six eventually meets up with the rest of Noble Team, and the Covenant begin glassing the city. As Noble Team is on their way to a fallout shelter under the Olympic Tower, Catherine-B320 is killed by an Elite Zealot's sniper fire.

August 25th
 * Dr. Halsey and Cortana choose the, with Jacob Keyes as its commander, for a secret mission Halsey is planning.

August 27th
 * All available SPARTAN-IIs gather at the FLEETCOM Military Complex on Reach, where they learn of their next mission: to acquire a Covenant vessel, navigate to the Covenant home world, and return with captured Covenant leadership.

August 29th
 * John-117 receives a neural interface upgrade, MJOLNIR Mark V armor, and is introduced to Cortana.
 * Noble Team is ordered to destroy Sword Base in a torch-and-burn op. During the operation, Noble Team makes their way inside Sword Base where they encounter Dr. Halsey, who asks them to protect her lab. Noble Team is then given direct orders to escort a fragment of Cortana holding crucial data from the Babd Catha Forerunner Complex to the Pillar of Autumn. Halsey is then escorted back to CASTLE base by Jun-A266.

August 30th
 * Cortana has ONI Colonel James Ackerson illicitly transferred to the front. This is her revenge for his attempts to eliminate both her and SPARTAN-117.
 * First Lieutenant Jake Chapman, along with most of Charlie Company is killed during the Fall of Reach.
 * The Covenant, despite sustaining heavy losses, wins a crushing victory at the Fall of Reach. Many of the remaining SPARTAN-IIs are killed.
 * The surviving SPARTAN-IIs on Reach are separated into two groups. One recovers Vice Admiral Whitcomb and goes into hiding at Camp Independence. The others are admitted into CASTLE Base by Dr. Halsey and receive parts of the MJOLNIR Mark V upgrade and new weapons.
 * Dr. Halsey learns of Colonel Ackerson's mysterious plans that seem to involve "her" Spartans.
 * SPARTAN-B312 destroys a CCS-class Battlecruiser with a mass driver to allow the Pillar of Autumn to escape Reach. The Spartan is killed by Sangheili soon after. The Autumn jumps away from the system, with Cortana using Forerunner navigation data from the Sigma Octanus IV Artifact as well as the Babd Catha Forerunner Complex.

September

 * The planet Coral is reported glassed by the Covenant.
 * The Battle of New Jerusalem takes place. After a chain of events involving a group of ODSTs attempting to steal gold from a bank vault, the 26th Marine Expeditionary Force is nearly wiped out, leaving the Rookie as one of few survivors. Eventually, the UNSC forces cut their losses and fall back to Earth.

September 4th
 * Lieutenant Wagner returns to Earth and reports on the evident destruction of Reach to Colonel James Ackerson, Admiral Hood, and Major General Strauss at HIGHCOM Facility Bravo-6 in Sydney, Australia.

September 14th
 * Earth's Orbital Defense Platforms are scheduled to come online.

September 19th
 * The arrives at Alpha Halo.
 * The Battle of Installation 04 begins.
 * SPARTAN-117 is awoken from cryo sleep and tasked with preventing Cortana's capture by the Covenant.
 * SPARTAN-117 and Cortana escaped the ship aboard a Bumblebee-class Lifepod, which later crashed on the ring.
 * The is forced to crash land on the ring. A significant portion of its crew survives to continue the fight on the ground.


 * Captain Keyes and the others in his escape pod are captured by the Covenant. Only Keyes escapes summary execution, and is taken to the Truth and Reconciliation.

September 20th
 * SPARTAN-117 leads a Marine force to board the Truth and Reconciliation. They recover Keyes and escape aboard a Covenant dropship. Keyes orders SPARTAN-117 to find the "Silent Cartographer", a map room that will reveal the location of the Control Room. Keyes leaves to lead an assault on a Covenant weapons cache.
 * Having found the map room and the pertinent information, Cortana directs a Pelican to take them to the area where the ring's Control Room is. Upon reaching the Control Room, Cortana transfers to the Control Room's computer and directs SPARTAN-117 to stop Keyes from accessing the 'weapons cache', really a Forerunner research and quarantine facility.
 * SPARTAN-117, without Cortana, enters the facility but is unable to locate Keyes. Instead, he discovers the "Flood" and is forced to retreat. He links up with marines and takes command of the surviving members of Keyes' team and together they fight their way to the extraction point. However, the Spartan is conscripted by the "Monitor of Installation 04" and teleported away before he can be evacuated with the surviving members.

September 21st
 * The Monitor takes John-117 to the ring's "Library" to retrieve the "Index", a device needed to activate the ring's primary weapon. Having retrieved the Index, the Monitor teleports the Spartan back to the Control Room where an irate Cortana confiscates the Index and prevents the ring from firing. SPARTAN-117 and Cortana flee a now-hostile 343 Guilty Spark and Sentinels.
 * To forestall the ring from being activated manually, SPARTAN-117 disables the ring's three Pulse Generators. This is to buy time to destroy the ring by activating the auto-destruct on the Pillar of Autumn. Only Keyes neural interface can activate the ship's self-destruct, and SPARTAN-117 embarks once more to rescue the captain.
 * Cortana teleports the Spartan to the Flood-overrun Covenant cruiser where Jacob Keyes is being held. Alas, the pair arrives too late to save Keyes, who has been merged into a Brain Form. SPARTAN-117 retrieves the neural interface by punching in the former-captain's head. Cortana downloads the necessary codes, and the duo returns to the Pillar of Autumn on a captured Banshee.

September 22nd
 * 343 Guilty Spark overrides the auto-destruct codes, forcing SPARTAN-117 to manually destabilize the ship's still-functioning fusion cores. SPARTAN-117 and Cortana then escape the resulting explosion and the fragmentation of the ring aboard a Longsword.
 * Staff Sergeant Johnson, Lieutenant Haverson, Warrant Officer Polaski, Corporal Locklear also escape the destruction of the ring aboard a Pelican.
 * SPARTAN-117 and Cortana rendezvous with Johnson's group in Installation 04's debris field. They also recover a set of cryotubes, one which contains SPARTAN-058.
 * The Battle of Installation 04 ends. Gunnery Sergeant Stacker and PFC Chips Dubbo survive, but it is unknown how they do.
 * Skirmish over Threshold: As the Longsword and Pelican are not jump capable, the UNSC survivors assault and capture the Ascendant Justice, a Covenant warship and apparently the flagship of the Covenant Fleet sent to Installation 04. They then set course for Reach.

September 23rd
 * A Time/Date Record Anomaly continues from this point in the narrative, resolved above on Sep 7, 2552.

September's Anomaly
After the recovery of a Forerunner device on Reach, the members of an organized resistance comprised of SPARTANs from Reach and survivors of the Battle of Installation 04 are in some sort of time anomaly, causing them not to be in the "correct timeline". What is known is that the events taken place with the possession of the device take place after September 7th.

September 7th
 * The Time/Date Record Anomaly of Sept 23, 2552 most likely rejoins the correct timeline.
 * Dr. Halsey and members of Red Team discover an enigmatic shard in a Forerunner installation below CASTLE Base. They are besieged by Covenant forces who seek to possess the shard.
 * The remaining Spartans, Admiral Whitcomb, Dr. Halsey, Sgt. Johnson, Lieutenant Haverson, Warrant Officer Polaski, and Corporal Locklear jump to Slipspace on board the Covenant/Human hybrid ship Gettysburg-Ascendant Justice, and discover that the shard seems to have the ability to bend both space and time.

September 12th
 * The Gettysburg/Ascendant Justice arrives for refit and provisioning in Eridanus system and meets with the rebels under Governor Jiles. Dr. Halsey sedates Spartan 087, Kelly, and absconds with her on Governor Jiles' personal ship, the Beatrice. Before she goes, she gives the alien artifact to Corporal Locklear, with implicit instructions to destroy it.

September 13th
 * UNSC forces aboard the Gettysburg/Ascendant Justice win a crucial victory at the Battle of the Unyielding Hierophant. SPARTAN-093, Lieutenant Haverson of ONI and Vice Admiral Whitcomb are killed. The survivors, now aboard the singular and with a captured Covenant slipspace drive, depart for Earth to warn of the impending Covenant invasion.

October
Unknown Date
 * An Edict from the Office of the High Prophet of Truth orders that in the virtue of the Jiralhanae, all Sangheili posted with the Fleet of Profound Solitude, the Fleet of Tranquil Composure, and the Fleet of Inner Knowledge to be completely replaced by Jiralhanae. Each removed Sangheili to be assigned other duties. In celebration, all imprisoned or criminal Jiralhanae were released, rehabilitated, and pardoned.
 * The is sent to Installation 04's debris field in the Soell System to scout the area for survivors. They detect the prison ship  and deploy Marines into the ship. Soon after, it is revealed that the ship is infested by the Flood and was used by the Office of Naval Intelligence as a laboratory to test the parasite on prisoners. The infestation is contained as the Red Horse unleashes a Shiva-class Nuclear Missile on the Mona Lisa, destroying it.

October 20th
 * SPARTAN-117 is outfitted with the MJOLNIR Mk. VI aboard Cairo Station.
 * The Fleet Commander of Particular Justice is deemed a Heretic by the Covenant High Council and sentenced to death.
 * SPARTAN-117 and Staff Sergeant (now promoted to Sergeant Major) Johnson are decorated at a ceremony aboard Cairo Station. Captain Keyes is awarded posthumously and the decoration is entrusted to Commander Keyes.
 * The Battle of Earth begins.
 * The High Prophet of Regret's fleet arrives at Earth, not expecting any human presence. The vastly outnumbered Covenant force attacks without seeking support from other Covenant forces.
 * SPARTAN-117 foils a Covenant attempt to demolish Cairo Station and commandeers the Covenant bomb to destroy an assault carrier.
 * The High Prophet of Regret's assault carrier breaks through the orbital defenses and initiates a ground assault on New Mombasa and the surrounding area.
 * SPARTAN-117 deploys to New Mombasa in an attempt to capture the High Prophet of Regret. Before this can happen, the assault carrier initiates a slipspace jump within the city, escaping Earth and severely damaging the city in the process. The, with SPARTAN-117 aboard, successfully pursues the carrier through slipspace.
 * Immediately after Regret's retreat, an additional Jiralhanae-led Covenant occupation force is inserted to New Mombasa, as a part of the Prophet of Truth's plan to eventually replace the Sangheili with the Brutes as the Covenant's primary warrior race. For the rest of the day, UNSC and Covenant forces battle for control of the city. Meanwhile, the Covenant fleet begins the process of uncovering the Ark Portal.
 * The former Fleet Commander of Particular Justice is made the Arbiter by the High Prophets of Truth and Mercy.
 * The Arbiter destroys a heretic group and 'recovers' the Oracle.

October 21st
 * The Battle of Mombasa ends with a Covenant victory.
 * In the dawn, Covenant reinforcements sent by the Prophet of Truth continue arriving at Earth to uncover the Portal.
 * Dare's Shock Trooper Squad escapes New Mombasa as the city, along with its surroundings are glassed by the Covenant excavation fleet.

October 20th through November 2nd
 * The Spartan-II Blue Team is deployed to defend Earth during the two weeks that follow the initial Covenant invasion. They participate in numerous combat missions on and around Earth, including Battle of Ross Island in the Antarctica and an underwater operation in the Yucatan Peninsula.

October 31st
 * The Battle of Onyx begins.
 * The standby signal rouse the Sentinels of Onyx, who destroy the UNSC base on the world.
 * Kurt, Mendez, and some Spartans battle to survive the Sentinel's onslaught.

November
November 2nd
 * The Battle of Installation 05 begins.
 * The UNSC In Amber Clad arrives at Delta Halo, following the High Prophet of Regret's assault carrier. SPARTAN-117, aided by ODSTs and marines, pursue the High Prophet to a Forerunner temple and assassinate him. However, orbital bombardment from the escorting fleets of the newly arrived High Charity destroys the temple. SPARTAN-117 is thrown into a lake and captured by Gravemind.

November 3rd
 * The UNSC Dusk arrives at Delta Halo and witnesses the final stages of the Battle of Installation 05. She retreats to Earth via a Slipspace Wake caused by the Forerunner ship.
 * Dr. Halsey and SPARTAN-087 arrive at Onyx and are trapped along with the rest of the human survivors. Halsey sends a distress signal piggybacked on Cortana's October 28 signal.
 * The Battle of Havana is fought. Having received Halsey's signal, SPARTAN-043, SPARTAN-058, and SPARTAN-104 redeploy from Earth to Onyx aboard a captured Covenant ship. They rendezvous with Halsey. The UNSC survivors are forced to retreat underground as a newly arrived Covenant fleet beings landing troops.
 * The Dusk arrives at Earth after mere hours. Upon arrival, she is re-assigned to Battlegroup Stalingrad. The group jump to Onyx via the captured Covenant Ships Slipspace wake.
 * Battlegroup Stalingrad arrives at Onyx to retrieve the survivors, but is unsuccessful due to the Covenant presence. The UNSC battlegroup is destroyed.
 * Onyx is found to be an artificial Shield World built by the Forerunners.
 * Kurt-051 dies after detonating 2 FENRIS warheads inside the Onyx Shield World structure.
 * Halsey and the other survivors hold off pursuing Covenant troops long enough to flee to the safety of the Shield World and seal the entrance.
 * Sentinels annihilate the remaining Covenant forces as Onyx's artificial landmass disintegrates.
 * The Battle of Onyx ends.
 * The Arbiter is sent to Delta Halo to retrieve that installation's Index. The Arbiter is successful, but is then betrayed by Tartarus, who casts the Arbiter into the depths of the ringworld. The Arbiter is subsequently captured by Gravemind.
 * Gravemind sends John-117 and the Arbiter to secure the Index and prevent the installation from being activated. SPARTAN-117 is teleported to High Charity while the Arbiter is teleported close to the Control Room.
 * The High Prophet of Truth transfers command of the Covenant Military to the Jiralhanae, and Tartarus orders them to wipe out the Sangheili. The Great Schism begins with the San 'Shyuum/Jiralhanae lead faction supported by the Kig-yar, Yanmm'e, and some Unggoy and Mgalekgolo, with the Sangheili supported by some Unggoy and Mgalekgolo.
 * The Gravemind manages to take control of the uses it to infest High Charity, which attack the High Prophet of Mercy, who is abandoned by the High Prophet of Truth. SPARTAN-117 is unable to stop Tartarus from leaving with the Index. Instead, on the advice of Cortana, the Spartan stows away aboard the Forerunner Dreadnought that is carrying the High Prophet of Truth to Earth. Cortana remains behind to ensure the destruction of Installation 05, should that become necessary.

November 3rd through November 7th
 * Cortana sends a slipspace message to Earth informing them that SPARTAN-117 is en route.
 * The Arbiter reaches the Control Room but is unable to prevent Tartarus from activating the ring. With the help of humans and the Elites, the Arbiter kills Tarturus. This allows Commander Keyes to physically remove the Index from the Core, temporarily interrupting the firing sequence.
 * Due to the interruption, Installation 05 automatically sends a signal to all other Forerunner installations in the galaxy, activating and placing them in standby mode.

November 8th
 * The Prophet of Truth arrives in the Sol System aboard the Forerunner Dreadnought, and proceeds on course towards Earth at near-relativistic speeds.

November 8th through November 17th
 * Before the Forerunner Dreadnought lands to Earth, Covenant Loyalist forces assault the human city of Cleveland, Ohio in the United Republic of North America on Earth. The Loyalists look for the Key of Osanalan, a mysterious Forerunner device related to the Halo Installations, which eventually turns out to be nonexistent.
 * Sergeant Major Johnson arrives back on Earth and gets clearance from Lord Hood to question Vergil about the artifact the High Prophet of Truth is digging up near Voi.

November 17th
 * The Forerunner Dreadnought enters Earth's atmosphere. Onboard is Master Chief Petty Officer John-117, who ejects from the ship, using a hatch as a heat shield upon re-entry. Meanwhile, Battle of Sector Six takes place at Pawa, Afghanistan. There, numerous Marines of the 2nd ODST Battalion track SPARTAN-117's descent. SPARTAN-117 eventually lands in the East African jungle near Mount Kilimanjaro, going unconscious for hours.
 * The Prophet of Truth's Dreadnought lands in the middle of The Artifact near Voi, Kenya. During the last few weeks, Truth's fleet of twenty-odd s and two Assault Carriers have almost entirely uncovered the artifact and occupied the entire region surrounding it.
 * SPARTAN-117 leads a UNSC counterattack to regain lost UNSC ground, retaking a jungle near Mount Kilimanjaro and securing the area around Crow's Nest, an underground facility used by the UNSC Defense Force to coordinate local Army, Navy, and Marine forces. The UNSC organize a small strike force led by SPARTAN-117 to attack the Covenant Loyalist-held Tsavo Highway, and thus have a platform for a strike at Voi.
 * The UNSC Marine Corps is able to retake the Tsavo Highway, and it serves for a staging ground for the battalion that would retake Voi. The UNSC forces stationed already at Voi have suffered severe casualties, with only pockets of Marines drawn in a scattered last defense against numerically superior and vehicle-supported Loyalist forces.
 * Fleet Admiral Sir Terrence Hood declares that it is imperative that SPARTAN-117's attack force retake Voi. Lord Hood's plan is that he will launch a low-level aerial strike on Truth's fleet above the Forerunner artifact, and prevent him from activating the presumed Ark. However, a Loyalist anti-aircraft emplacement stationed at Voi is preventing Hood's fleet from advancing; SPARTAN-117 is to retake Voi and destroy the anti-aircraft emplacement to allow Hood to attack Truth's fleet, and prevent him from activating the Ark.
 * They later defeat the AA guns, opening up a pocket in the Loyalist Defenses for the Home Fleet to come in and engage Truth's forces. They are unsuccessful in damaging the Dreadnought, and it escapes through the Portal. At the same moment, a Flood-controlled ship slips in, crashing in Voi.
 * Commander Miranda Keyes orders her troops to fight to the core of the Flood Battlecruiser and overload its reactors, destroying the ship and the town and any Flood along with it. The Fleet of Retribution, having followed the Flood infected ship from their blockade at Installation 05 to its arrival at Earth, begins to drop forces to push towards the ship, seeking something that lay within it. It isn't until they come back into Traxus Facility that the Sangheili tell the UNSC that Cortana, the AI formally attached to the Spartan-IIs, the, and companion of John-117, is supposedly on the downed ship.
 * The joint UNSC/Separatist force press on to the crash site and eventually break through, fighting past hordes of Flood. With the remaining forces giving cover to the Chief, he enters its Flood created carcass and retrieves what is believed to be Cortana. After the ground forces are evacuated safely the Elites begin to glass the immediate area, annihilating the Flood and eliminating any chance of further Flood infection, effectively ending the Battle of Voi.

Late November through December
The end of 2552 saw the bloodiest period of the Great War and the beginning of the end. The Prophet of Truth was killed in the later months along with a sizable Covenant armada, leaving the Covenant forces crippled and leaderless as well as the full destruction of Gravemind and its Flood forces.

Battle of Installation 00

 * The Prophet of Truth, having successfully activated the artifact in Kenya, left Earth through a Slipspace portal to the Ark, a Forerunner structure that could be used to fire all of the Halo installations at once.
 * Despite Lord Hood's urging, Commander Keyes took ships from the Home Fleet with a small fleet of Separatist cruisers led by the carrier Shadow of Intent and proceeded through the Slipspace portal and arrived at the Ark.
 * The Separatists on arrival immediately engaged the Loyalist fleet stationed to protect the Prophet while the Forward Unto Dawn deployed Marine Shock Troopers to locate Truth. Despite being outnumbered 3-to-1 in space, the Separatist fleet made short work of the Loyalist space forces, likely due to the Elites' superior tactical skills. The Covenant Loyalist Fleet had been destroyed and the only Loyalists left alive were Truth and his forces on the Ark. 343 Guilty Spark, now working with the UNSC-Separatist Alliance, led SPARTAN-117 and the Arbiter to the Ark's Cartographer where they pinpointed the Prophet's location. By then Truth had already holed himself in a secure facility near the core of the Ark and had activated a large barrier around the entire core to ward off the attacking forces.
 * The UNSC ground forces, along with Separatist reinforcements, assaulted three emitter pylons that powered a small section of the barrier. When the defending forces were eliminated and the pylons shut down, the Shadow of Intent began its attack on Truth. At the same time the former Covenant city ship High Charity arrived from slipspace and crashed on the Ark. Debris, spread from the city-ship, heavily damaged the Shadow of Intent and helped spread a new Flood infestation on the Ark as a means to stop Truth and to be safe from the Halo activation array. Without any heavy support, SPARTAN-117 and the Arbiter personally attacked the facility where Truth was to activate the Halo installations.
 * Sergeant Major Johnson, who had disappeared during the assault on the towers, was in fact captured by Truth's forces and was being tortured into pressing the final switch to activate the other Halos, as fail-safes within the structure prevented anyone other than a Forerunner or a Reclaimer to do so. With SPARTAN-117 and the Arbiter too far away to stop Truth, Commander Keyes grabbed a Pelican dropship and crashed into the facility to rescue Johnson, but was killed soon thereafter by Truth himself. The Gravemind dispatched Flood forces to assist SPARTAN-117 and the Arbiter in order to prevent the activation of the Halo Array system; their support enabled the Master Chief and the Arbiter to reach Truth in time. The Arbiter personally killed Truth with his sword. However, the Gravemind betrayed the two of them after knocking them out of Keyes' Pelican,(then piloted by Johnson and also carrying the Commander's body), thwarting their plan of escape and forcing SPARTAN-117 and the Arbiter to fight their way outside.

Raid on High Charity

 * 343 Guilty Spark had managed to facilitate the making of a new Halo through the Ark, explaining that a tactical pulse from it would eliminate the Flood infestation. However, this new Halo lacked an Activation Index. The only way they could get another Index was to rescue Cortana from High Charity since she still possessed the Index from Installation 04. Through a tough battle, SPARTAN-117 and the Arbiter successfully entered the ruins of High Charity and recovered Cortana, using a partly-damaged Pelican to escape while High Charity was destroyed when its reactors went critical after the Spartan blasted them.

End of Human-Covenant War

 * With the Index secure, the Arbiter ordered that the remaining UNSC forces relocate to the Separatist ships and escape back through the Slipspace portal to Earth while he, SPARTAN-117 and Sergeant Major Avery Junior Johnson moved in on the Control Room of the incomplete Halo, the latter coming in alone aboard the Forward Unto Dawn. The Dawn was left behind as the only means of escape. By now what was left of the Gravemind had relocated to the new Halo. The Arbiter, Johnson, and SPARTAN-117, along with 343 Guilty Spark made it through waves of Flood to the Control Room. 343 Guilty Spark explained that the new Halo would be ready to fire within a few days, but with Flood moving in all around them Johnson explained the necessity of firing the ring immediately, prompting Guilty Spark's protest that activating Halo now would destroy both the Ark and the installation, and Johnson's subsequent reply of, "deal with it," as he prepared to activate the ring. Unwilling to let "his" ring be destroyed again, Spark went rampant, attacking Johnson, SPARTAN-117, and the Arbiter. However, with the help of mortally-wounded Johnson and his laser, SPARTAN-117 managed to destroy Guilty Spark and start the firing sequence for the new Halo. Just after Johnson's final remarks to SPARTAN-117, he died. SPARTAN-117 and the Arbiter then escaped the control room by taking Johnson's Warthog to the Forward Unto Dawn. Due to the unstable, incomplete nature of the ring as it fired, the Slipspace portal collapsed as the Dawn entered it, causing it to be sheared in two. The forward half with the Arbiter made it to Earth, crashing into an ocean (presumably the Indian Ocean). Cortana and SPARTAN-117 were in the hangar area at the time of the separation, and were thus left in the aft section of the ship, which fell out of Slipstream space at an unknown location, eventually drifting towards an unidentified planet.

December
December 31st
 * Codename: SURGEON filed a report to Codename: USUAL SUSPECTS entitled "Historical/Psychological Analysis of Cole, Preston J." The report was filed from in synchronous orbit on the far side of Luna.

Battles
Human-Covenant War
 * Battle of Sigma Octanus IV
 * Battle of Reach
 * Battle of Installation 04
 * Raid on the Truth and Reconciliation
 * Battle of the Silent Cartographer
 * Massacre at Eridanus Secundus
 * Operation: FIRST STRIKE
 * Battle of Earth
 * Battle of Mombasa
 * Battle of Havana
 * Battle of Cleveland
 * Battle of Sector Six
 * Battle of Voi
 * Battle of the Gas Mine
 * Battle of Installation 05
 * Battle of Onyx
 * Battle of Mare Erythraeum
 * Battle of Installation 00

The Great Schism
 * First Battle of High Charity

Quarantine of the Flood
 * Quarantine of Installation 05
 * Battle of the Quarantine Zone
 * Second Battle of High Charity

Notable deaths
Human


 * Amey
 * Ackerson, James - Colonel
 * Ackerson, Ruwan
 * Benti, Ngoc - Hospital Corpsman
 * Bisenti - Private
 * Buckman - Lieutenant
 * Carter, Tink - First Sergeant
 * Chapman, Jake - First Lieutenant
 * Charleston
 * Clarence
 * Corly - Sergeant
 * Brien, Connor
 * Courage, Jake - War Photographer
 * Dale
 * Dalu - Second Lieutenant
 * Dowski, Ellen - Ensign
 * Endesha - Doctor
 * Fitzgerald, M. - Private First Class
 * Hague
 * Hale, Rick - Lieutenant
 * Haverson, Elias - Lieutenant
 * Herzog - Colonel
 * Hikowa, Aki - Lieutenant
 * Hosky - Private First Class
 * Keyes, Jacob - Captain
 * Jenkins, Wallace - Private First Class
 * Jiles, Jacob - Governor
 * Johnson, Avery - Sergeant Major
 * Jones - Lance Corporal
 * Kappus - Private
 * Keyes, Miranda - Lieutenant Commander
 * Kits - General
 * Lister - Master Sergeant
 * Locklear - Corporal
 * Lovell, William - Ensign
 * Lovik - Corporal
 * Marcus, Samuel - Petty Officer Third Class
 * McCasky - Second Lieutenant
 * McKay, Melissa - First Lieutenant
 * McKenzie - Private
 * Mendoza, Manuel - Private
 * Mitchell - Corporal
 * Mobuto, Marvin - Staff Sergeant
 * Nixaliz
 * O'Brien - Private
 * Oros - Second Lieutenant
 * Orrin
 * Parker - Sergeant
 * Perez - Corporal
 * Rimmer, Patrick
 * Riley - Private
 * Postly, Marie - Private
 * Polaski, Shiela - Warrant Officer
 * Rawley, Carol - Flight Officer Captain
 * Purdy, Gail - Lieutenant Commander
 * Sanderson, Felicia - Colonel
 * Silva, Antonio - Major
 * Shephard, Thom - Chief Petty Officer
 * Satha - Private
 * Santiago, Eric
 * Sita
 * SPARTAN-051: Kurt - Lieutenant Commander
 * SPARTAN-052: Jorge – Warrant Officer
 * SPARTAN-?293: Thom - Unknown
 * SPARTAN-A239: Emile – Warrant Officer
 * SPARTAN-A259: Carter - Commander
 * SPARTAN-B312 - Lieutenant
 * SPARTAN-B320: Kat – Lieutenant Commander
 * Teller - Teller
 * Vern
 * Waller - Gunnery Sergeant
 * Whitcomb, Danforth - Vice Admiral
 * Yevgenny, Gage

Sangheili
 * Imperial Admiral Xytan 'Jar Wattinree (Presumed dead by the NOVA activation near Joyous Exultation)
 * Fleet Master Voro Nar 'Mantakree
 * Field Master Noga 'Putumee
 * Heretic Commander Sesa 'Refumee
 * Shipmaster Orna 'Fulsamee
 * Special Operations Officer Zuka 'Zamamee
 * Ado 'Mortumee
 * Isna 'Nosolee
 * Soha 'Rolamee

San 'Shyuum
 * High Prophet of Regret
 * High Prophet of Mercy
 * High Prophet of Truth
 * Prophet of Stewardship
 * Minister of Etiology
 * Minister of Inquisition

Jiralhanae
 * Chieftain of the Jiralhanae Tartarus
 * Ceretus
 * Jiralhanae Chieftain Parabum
 * Maladus
 * Facius
 * Hammadus
 * Jupentus
 * Brunus
 * Golubus

Unggoy
 * Gagaw
 * Linglin
 * Yayap
 * Zawaz
 * Kwassass
 * Flipyap

Yanme'e
 * Hopalong

Forerunner
 * 343 Guilty Spark
 * 032 Mendicant Bias (Presumed destroyed with the Ark)

Flood
 * Gravemind

Trivia

 * The first and second parts of 2552 equal 2+5=7 and 5+2=7, another one of Bungie's 7 references.