Battle for Earth

"Earth...is all we have left."

- Lord Terrence Hood

The Battle of Earth was a very large and prolonged engagement between the Covenant and the United Nations Space Command, which occurred on and above the planet Earth, inside the Sol System from October 20, 2552 to November 17th, when the Prophet of Truth's Dreadnought left Earth through the Portal.

Truth Strikes Toward Earth
The Covenant discovered the location of Earth after the Battle of Reach. The Prophet of Truth withheld knowledge of this discovery from the Covenant and other high ranking officials. . To attack the UNSC homeworld, he ordered an assault fleet to secretly assemble at Unyielding Hierophant station in the Tau Ceti System. The fleet would overwhelm Earth's defenses in a single decisive strike.

The Covenant assault fleet was discovered by the UNSC AI Cortana. A pre-emptive strike led by Vice Admiral Danforth Whitcomb and SPARTAN-II John-117 destroyed Unyielding Hierophant and almost the entirety of the assembled fleet, some 500 ships. Earth was granted a small reprieve.

Regret Strikes Toward Earth
The Prophet of Regret also learned of the location of Earth, albeit indirectly. He discovered the location of the Portal, a Forerunner artifact leading to the Ark, and set off to uncover it. The Prophet was not aware that the Portal was located on Earth; not being privy to Truth's information, Regret unknowingly led his small fleet, a mere two Assault Carriers and 13 s, straight into Earth's formidable defenses.

Truth belatedly learned of Regret's attack, and dispatched a large Jiralhanae-led fleet to reinforce the attack. They arrived only after Regret had fled.

Regret Arrives
"Something's not right. The fleet that destroyed Reach was fifty times this size!"

- Fleet Admiral Terrence Hood

Regret's fleet was detected near Io, Jupiter, as a series of Slipspace "whispers". Probes were sent to investigate, but shortly afterward the Covenant fleet reverted to realspace near Earth, just outside the killzone of the planet's Orbital Defense Platforms (ODPs). UNSC forces went to TACCON Alpha 2. Fleet Admiral Harper ordered his fleet to attack, but quickly received new orders from Fleet Admiral Terrence Hood to fall back and defend the ODPs.

The Assault Carriers converged on the battle cluster including Athens Station, Cairo Station and Malta Station. The ODPs opened fire as the enemy entered range. Covenant troops boarded the stations bringing, intending to demolish them with an Antimatter Charge each. As each bomb was planted the Covenant withdrew. Athens and Malta were demolished in quick succession. Cortana, aboard Cairo, deduced the nature of the threat and John-117 was despatched to prevent the same fate from befalling Cairo.

Cortana directed the SPARTAN-II to the bomb's location in Cairo's fire control center. En route to the bomb, John-117 rescued Commander Miranda Keyes and allowed her to board. The frigate departed Cairo to join the fray.

The Covenant Break Through
The two Assault Carriers began to break through toward Cairo. Cortana directed Cairo SMAC against Regret's Carrier, but the ship did not stop to engage and instead made directly for New Mombasa on the surface. Admiral Harper led the attack on the second carrier and depleted its shields. Keyes volunteered to attack the carrier immediately, but Hood was unwilling to pit a single frigate against so large a target.

The solution to the second carrier came from an unexpected angle. John-117 and Cortana managed diffuse and capture the Covenant antimatter bomb aboard Cairo, and the Spartan volunteered to go EVA and personally plant the bomb on the last carrier. Hood agreed. John-117 leapt out of an airlock with the bomb using only the initial explosive decompression for impulse. Longsword interceptors opened a breach in the carrier's hull and allowed the Spartan to infiltrate and plant the bomb internally. The detonation destroyed the ship. John-117 escaped using the same means he had arrived and free fell to the UNSC In Amber Clad.

Ground Battle


"Dear Humanity, we Regret being alien bastards, we Regret coming to Earth, and we most definitely Regret the Corps just blew up our raggedy-ass fleet!"

- Avery Johnson commenting on Regret's message.

Regret's carrier came to a stop above the city of New Mombasa in the East African Protectorate. From there the first Covenant troops to ever set foot on humanity's homeworld engaged in the first land engagement of the Battle of Earth. The UNSC In Amber Clad descended near Mombasa, and deployed three Pelicans, one with Spartan-117 onboard, with the intent of infiltrating the Carrier and capturing the Prophet of Regret. However, all of the dropships were shot down by a Covenant Scarab in Old Mombasa. Spartan-117, with the assistance of numerous Marines, made his way through Old Mombasa, to NM 105E, and across the bridge to New Mombasa Sector B, where the Scarab was eventually trapped and destroyed. During the battle's final moments, the Covenant forces started to retreat back to the Carrier.

Meanwhile in orbit, Regret's fleet was nearly defeated, with the UNSC taking heavy casualties. Ships of the Home Fleet, including the in Earth's low orbit, deployed teams of ODST, most of which were tasked with assaulting the Carrier by breaching its hull. However, one of these teams was chosen by an ONI operative to partake in a mission to secure the city's infrastructure A.I. the Superintendent from falling into enemy hands.

Regret's Retreat
"Slipspace rupture off the target's bow! It's going to jump - inside the city!"

- A bridge officer reporting to Commander Keyes.

Seeing the Carrier was retreating, Commander Keyes ordered Spartan-117 to be extracted back to the In Amber Clad. Moments after this, the Carrier jumped into slipspace while still above the city, with the In Amber Clad following in its wake. The ODSTs were still on their way, and could do nothing but watch as the carrier's slipspace rupture generated a massive shockwave, which severely damaged the city, as well as an EMP, which disabled the ODSTs' drop pods' electronic systems, plunging the pods into uncontrolled freefall. They were scattered around the city, the ones close to the carrier presumably killed by the slipspace rupture.

Covenant Occupation
"The Covenant have found Earth. They own New Mombasa. Anyone that could've driven them off is dead, or gone. I'd say that makes for desperate times."

- Edward Buck

Immediately following the slipspace event, Prophet of Truth's Jiralhanae-led reinforcements arrived. Under orders from Truth, the Jiralhanae took command over the remaining ships from Regret's fleet, killing their Sangheili crews. A Jiralhanae-led occupation force was also inserted into New Mombasa, where they killed any remaining Sangheili infantry. This was a part of the Prophet of Truth's plan to eventually replace the Sangheili with Brutes as the Covenant's primary warrior race.

The surviving UNSC and NMPD clashed with this force for control of the city. A squad of ODSTs, with the assistance of Marine and NMPD survivors, as well as the city's AI Superintendent, participated in various battles. Despite their efforts, the city was eventually lost to the Covenant due to their overwhelming force. After this, the recently-arrived Covenant ships started uncovering the Portal to the Ark, glassing the Mombasa area along with its surroundings.

In the following weeks, the desperate battle for Earth was far from over. More Covenant occupation ships arrived, attacking targets and digging for Forerunner artifacts around the globe, with ships in orbit battering the UNSC Home Fleet. The Spartan Blue Team, SPARTAN-104, SPARTAN-058, and SPARTAN-043 partook in numerous battles around Earth, including many orbital zero-gravity operations, the Battle of Ross Island in the Antarctica where they neutralized a Covenant excavation with a HAVOK tactical nuke. Operating from Base Segundo Terra in Mexico City, they performed an underwater mission off the Yucatan Peninsula, and on November 3, they partook in the Battle of Havana in Cuba, which ended in the Centennial Orbital Elevator collapsing. After this, the team was re-directed to aid Dr. Halsey on Onyx. They captured the Bloodied Spirit and headed straight for Onyx.

With the Spartans gone, during the weeks that followed, almost the entire UNSC resistance on Earth was crushed, at least in the East African Protectorate. The Covenant set up heavy defenses around their excavation for the Ark Portal, including heavy AA Batteries in Voi and the surrounding regions. The constant orbital battle left the UNSC Home Fleet's numbers greatly reduced. During this time, unbeknownst to the Covenant, the UNSC reactivated an old military base, Crow's Nest near Voi.

Truth's Arrival
"Master Chief, you mind telling me what you're doing on that ship?"

- Fleet Admiral Terrence Hood

"Sir, finishing this fight."

- Master Chief

On November 3, the Prophet of Truth left High Charity in the Forerunner Dreadnought, destined to arrive at the Sol System on November 8, unknowingly carrying the stowaway John-117, returning to "finish the fight". The Prophet of Truth's intention was to activate The Ark, fire the Halo rings, and begin what he thought would be the "Great Journey".

During the ongoing battle in Sol system, the Covenant forces invaded the city of Cleveland on Earth, looking for an artifact known as the "Key of Osanalan", which eventually turned out to be a hoax. During this time, Sergeant Major Avery Johnson, Arbiter and Commander Miranda Keyes arrived at Earth from Installation 05, Commander Keyes taking command of Crow's Nest on the ground.

On November 17, the Forerunner Dreadnought reached Earth. SPARTAN-117 - the Master Chief, escaped by jumping from the ship and entered Earth's atmosphere, crashing into an East-African jungle. Meanwhile, a battle took place in Earth's Sector Six, Afghanistan, where a group of Marines struggled to retrieve a Laser Designator, which they used to track the Spartan's fall, making locating him easier.

Turning point
"The Commander's come up with a good plan. But without you, I wasn't sure we could pull it off."

- Lord Hood to John-117 at Crow's Nest

In the morning, the Master Chief was retrieved by Sergeant Johnson, along with the Arbiter and a group of Marines. The company then fought their way through the Covenant captured territory and were extracted and taken to the Crow's Nest - one of the last UNSC strongholds and bastions in Africa. Here, Commander Miranda Keyes and Lord Hood planned a last-ditch and last-resort effort to cease Truth's activation plan.

Shortly after the Chief's arrival, however, the outpost was discovered and quickly attacked by Covenant forces. After the base was taken over, the UNSC forces decided to destroy it using a bomb, killing all the Covenant in the base. The Master Chief activated the bomb and was barely able to escape the explosion.

Scattered, the UNSC forces then fled the base along the Tsavo Highway, regrouping on their way out. Soon, they were given orders by Commander Keyes to head to the city of Voi. Spartan-117, with the help of Marines, crushed Covenant resistance on the Highway, clearing the way to Voi.

Counterattack
"Marines, the Prophet of Truth doesn't know it yet, but he's about to get kicked right off his throne. You will take our city back. And drive our enemy into the grave they've been so happily digging. One final effort is all that remains."

- Admiral Terrence Hood

Upon reaching Voi, the Humans, with almost all organization collapsing, launched one last desperate plan. With the help of the Master Chief, the human forces destroyed a small section of the defenses around Truth and the artifact, allowing Lord Hood to lead the last reserves of ships in an attempt to destroy it.

Nothing came out of this however, because the human ships did seemingly no damage to Truth's ship, who activated the artifact, creating a large Slipspace portal into which most, if not all of the Covenant Loyalist ships on Earth retreated.

Flood on Earth
"Quickly! Let us find their ship. Make short work of this abomination!"

- Thel 'Vadam

At this exact moment, a Flood-controlled ship arrived at Earth, crashing in Voi. It infested the area around the Portal, quickly spreading throughout the city of Voi.

The UNSC decided to contain the infestation by detonating the Flood ship's reactor, a task which was assigned to Spartan-117. Soon after this, Covenant Separatists arrived from their quarantine of Delta Halo, having chased the Flood ship. They deployed teams of Elites to the ground, to retrieve the UNSC AI construct, Cortana, which they believed was being held inside the Flood-controlled ship, and after this, glass the area to destroy the Flood threat. Spartan-117 and the Arbiter, with the assistance of several Elites, fought their way through the Flood-infested city to retrieve Cortana's message (which they thought was Cortana) from the Flood ship, after which they were extracted to the Separatists' flagship, the Carrier Shadow of Intent, as the city of Voi and surrounding countryside were glassed by the Separatist fleet, destroying the Flood threat.

Aftermath
"And you, Shipmaster just glassed half a continent! Maybe the Flood isn't all I should be worried about."

- Terrence Hood

"One single Flood spore can destroy a species. Were it not for the Arbiter's counsel, I would have glassed your entire planet!"

- Rtas 'Vadum

After retrieving the storage device which was believed to contain Cortana, Spartan-117, met by the monitor 343 Guilty Spark, joined the remaining UNSC Navy leadership, Lord Hood and Commander Keyes, aboard the Shadow of Intent, to see if Cortana's damaged storage device could be repaired.

It turned out to be just a message, recorded by Cortana who was held captive by Gravemind in High Charity. Cortana had acquired information about the Portal, and that on its other side there was a solution to stop the Flood once and for all. She also warned about the flood-infested High Charity, which was approaching Earth. From this, Admiral Hood decided to remain on Earth and desperately attempt to defend it against the Flood, while the Covenant Separatists, along with UNSC forces led by Commander Keyes would go through the Portal, as they realized there was no way to win if the Flood would attack humanity's homeworld.

Apparently, the Flood attack to Earth never came. Upon arriving at Earth, High Charity went straight through the Portal, without launching an assault on Earth. It eventually arrived at Installation 00, joining the battle raging on the installation.

Despite having suffered enormous military and civilian losses, the UNSC regained control of Earth and with the defeat of the Covenant Loyalists and the Flood on Installation 00, the war finally ended in a human victory. The humans have initiated reconstruction in order to repair the damage inflicted on humanity as a result of the Battle of Earth.

Timeline
The following is a timeline of the battle.

October 20, 2552
 * Lord Hood awards SPARTAN-117, Sergeant Johnson and Jacob Keyes (posthumously) medals for their efforts during the Battle of Installation 04 and subsequent actions. Miranda Keyes received the medal posthumously given to her late father, Captain Keyes. The ceremony takes place on Cairo Station.
 * A Covenant task force of 2 Assault Carriers and 13 s exits Slipspace just beyond the range of the MAC satellites.
 * It is speculated that at this time, the warning sirens heard in the ilovebees storyline begin shortly after this Covenant sighting.
 * Fleet Admiral Harper, in charge of the Earth defense fleet, responds rapidly with an attempt at a counter attack, preparing all available vessels to engage the Covenant. This order is overruled by Lord Hood.
 * The Covenant launch waves of boarding craft toward the orbital defense stations. Several UNSC vessels and stations are destroyed by boarding Covenant forces.
 * The MAC platform Malta, after sending elated communications that they have repelled all Covenant boarders, is annihilated in a cataclysmic explosion. The shockwave of which is felt by the crew of the Cairo station, demonstrating just how large the detonation was. Shortly afterward the Athens MAC platform experiences the same fiery fate.
 * It is deduced that both explosions came from within each of the stations - the Covenant boarding parties had brought with them a bomb. As a result, all personnel on orbital platforms redouble their efforts against Covenant boarders.
 * The Cairo MAC platform is saved by the heroic efforts of Spartan-117, single-handedly disarming (with the aid of Cortana who was acting as the platform's AI) and removing the Antimatter Charge from the orbital platform. The Master Chief removes the explosive device by jettisoning it, along with himself, out of a docking bay airlock. He then uses this same bomb to destroy a Covenant Assault Carrier that had just broken through the UNSC's defensive perimeter.
 * During a protracted naval engagement, a Covenant Assault Carrier blows through the Malta's debris field and heads straight for Earth. It comes to a stop above the city of New Mombasa in the East African Protectorate.
 * From there, the first Covenant troops to ever set foot on humanity's homeworld engage in the first land engagement of the Battle of Earth.
 * UNSC forces engage the Covenant on the ground and wage a bloody street-by-street skirmish in both Old and New Mombasa.


 * After some time of ground battle and complete evacuation of Mombasa, SPARTAN-117, along with several Marines, are sent to crush the Covenant resistance in the city and infiltrate the Prophet of Regret's Assault Carrier above the city, complimented by an ODST force which would be inserted from orbit directly into the Assault Carrier, though one squad's mission was actually separate.
 * The arduous ground war is ended with the Prophet of Regret's Assault Carrier making a sudden Slipspace jump only hundreds of meters above the city of New Mombasa. His motivations for doing so were, at the time, unknown. The Assault Carrier is followed by the, which, upon arrival begins the Battle of Installation 05.
 * This atmospheric Slipspace jump severely damages the City of New Mombasa. The ODSTs' drop pods are scattered around the city, most of them presumably killed by the slipspace rupture.
 * Immediately following the slipspace event, Truth's backup fleet arrives and engages UNSC forces in orbit. The Jiralhanae overtake the Sangheili on both the ground and in space while continuing to engage the UNSC. A Jiralhanae-led occupation force is also inserted into New Mombasa. The surviving UNSC and NMPD forces clash with the Covenant for control of the city.

October 21, 2552
 * Eventually, the city of New Mombasa occupied and its surroundings glassed by the Covenant, to uncover the Artifact, ending the battle of Mombasa in a Covenant victory. However, the UNSC manages to extract a defecting Huragok from the city and use it to gain intel on the Covenant's goals.

October 20 through November 3, 2552
 * SPARTAN Blue Team is deployed to defend Earth during 's disappearance. They participate in numerous combat missions around the world, including the Battle of Ross Island in Antarctica.

November 3, 2552
 * SPARTAN-104, SPARTAN-058, and SPARTAN-043 partake in the Battle of Havana. Shortly thereafter, they use a captured Covenant Destroyer to depart for Onyx.
 * The Forerunner Dreadnought, with the Prophet of Truth aboard, departs High Charity for Earth.

November 8, 2552 November 17, 2552
 * The Forerunner Dreadnought arrives in the Sol system and proceeds to Earth at near-relativistic speeds.
 * The Forerunner Dreadnought arrives at Earth. Spartan 117 ejects, landing in Kenyan jungle. In the following morning, Spartan-117 is recovered by a group of Marines led by Sergeant Johnson.
 * The Marines, with Spartan-117, make their way to Crow's Nest, where a plan for a counterattack is devised. The base is invaded by the Covenant, and eventually destroyed by the UNSC.
 * The UNSC forces regroup along Tsavo Highway, eventually assaulting the Covenant-held town of Voi.
 * UNSC Forces neutralize Covenant Anti-Air defenses in Voi. A battle group from the UNSC Home Fleet initiate the assault on the Forerunner Dreadnought, with no effect. The Artifact is activated. Covenant Loyalist forces flee to Installation 00 through the Portal.
 * Immediately thereafter, a Flood-controlled ship emerges from Slispace over Voi, crashing to the town. Flood infestation starts spreading around the region. Covenant Separatist fleet, having given chase, arrives at Earth and glasses Voi as well as its surroundings.
 * A transmission from the UNSC AI Cortana is retrieved from the Flood ship. The Covenant Separatist forces, with several UNSC forces with them, go through the Portal to the Ark.

UNSC

 * ODA-143 Malta Station
 * ODA-142 Cairo Station
 * ODA-144 Athens Station
 * Nassau Station

Covenant

 * Forerunner Dreadnought
 * Pious Inquisitor (Pre-Great Schism)
 * Regret's Carrier
 * Harbinger of Piety
 * Triumphant Declaration

UNSC Marine Corps

 * 2nd Shock Troops Battalion (Unknown Regiment)
 * 7th Shock Troops Battalion (Unknown Regiment)
 * 1st Platoon (Unknown Company and Regiment)
 * 3/1 Bravo
 * 405th
 * A Company
 * 17th Marine Regiment
 * 77th Marine Regiment
 * E2-BAG/1/7
 * M/LAT-16
 * S/VRC-8
 * S4/BLCE/1/7
 * S4/BRT/1/7
 * Alpha Company
 * Charlie Company

UNSC Navy

 * UNSC Home Fleet
 * Second Fleet
 * Seventh Fleet
 * Sixteenth Fleet
 * 6th Battle Group
 * Harper's Fleet

Covenant

 * Regret's Fleet
 * Truth's Fleet
 * Fleet of Furious Redemption

Covenant Separatists

 * Fleet of Retribution

UNSC

 * Fleet Admiral Sir Terrence Hood
 * Fleet Admiral Harper
 * Unnamed UNSC Navy Captain
 * Captain Veronica Dare
 * Commander Richard Lash
 * Lieutenant Commander Miranda Keyes
 * Lieutenant Commander Julian Waters
 * Lieutenant Commander Xaing Cho
 * Lieutenant Bethany Durruno
 * Lieutenant Joe Yang
 * Lieutenant Parisa
 * Lieutenant Junior Grade SPARTAN Frederic-104
 * Master Chief Petty Officer SPARTAN John-117
 * Sergeant Major Avery Junior Johnson
 * Gunnery Sergeant Pete Stacker
 * Petty Officer Second Class SPARTAN Linda-058
 * Petty Officer Second Class SPARTAN William-043
 * Unnamed Marine Officer
 * Staff Sergeant Marcus Banks
 * Gunnery Sergeant Edward Buck
 * Gunnery Sergeant Pete Stacker
 * Corporal Taylor H. Miles
 * Corporal Palmer
 * Corporal Perez
 * Corporal T. Rymann
 * Lance Corporal Kojo Agu
 * Lance Corporal "The Rookie"
 * Lance Corporal Morton
 * Lance Corporal Pineada
 * Private First Class Michael Crespo
 * Private First Class Chips Dubbo
 * Private First Class Locke
 * Private First Class Galliard
 * Private First Class Sullivan
 * Private McKenzie
 * Private Emerson
 * Private Jemison
 * Private Scottlee
 * Private S. Hartley
 * Corpsman R. Coney
 * Unnamed Corpsman

Covenant

 * High Prophet of Regret
 * High Prophet of Truth
 * Minister of Inquisition
 * Lepidus
 * Vergil

UNSC

 * 12-9F5
 * 957-A3
 * Echo 51
 * Kilo 23
 * Oscar 6

Additional Notes And Theories
At the beginning of the battle, fifteen ships and their personnel, led by the Prophet of Regret were defeated by a much larger and more powerful human fleet and ground forces. The battle itself was caused by miscommunication and lack of co-ordination between members of the Covenant, specifically the failure of the Prophet of Truth to inform the Prophet of Regret that Earth was in fact very heavily and well defended. The lack of information available to Regret meant that he was surprised and outgunned by the human defenses.

UNSC High Command found it puzzling, to say the least, that a Covenant fleet of such small size, carrying a Prophet, would be their first engagement in the defense of Earth. The fleet that glassed Reach was fifty times the size of this new threat. To attack such a heavily prized and defended world, a fleet of greater size than the fleet at Reach would be required.

Not only this, the fact that only one city on Earth was attacked left UNSC strategists baffled. At the bare minimum the invading force would have to attack and occupy multiple areas, providing at least some strategic benefit, synchronously. Given the Covenant's tactical history it seemed unlikely that they would be prone to overconfidence.

Compared to the invasion force at Reach the two simply did not match up. The Covenant force at Reach was not only massive in numbers, it was knowledgeable of the terrain. The invasion force at Earth was small and displayed confusion (not an attribute the Covenant are known for).

The fleet that attacked Reach even took their time glassing the surface prior to sending in ground forces. Again the fleet that attacked Earth did almost the exact opposite, rushing to get to the surface. These observations could suggest that this Covenant fleet was not an invasion fleet at all but rather a planetary reconnaissance, search, and dig team.

Although capable of combating a small colony and/or aggressive native lifeforms, the expeditionary fleet lacked the strength in force or numbers for a full-scale invasion attempt. Speculation arose that, following the Covenant's discovery of Delta Halo, they found some form of Forerunner technology that led them to the location of a Shield World.

Another possible scenario explaining the events, but highly inadmissible due to lack of timeline during the events of Halo 2, is that after the seizure of 343 Guilty Spark, and subsequent interrogation, the location of the end of their pilgrimage was located. Even if the specific name "Earth" was used by the monitor, it would have raised no caution in the Covenant ranks; to their knowledge, the location of planet Earth was unknown to humans. It could be hypothesized that due to the assuming nature of Forerunner Monitors, Guilty Spark would have made no mention of Humans living there unless specifically asked.

There is also the suggestion that the Covenant were following a signal which emanated from the Forerunner Deep-Space Artifact brought to Earth aboard the Apocalypso when it was deactivated by Jersey Morelli. The burst of EMP, Slipspace, and Realspace signals could be what drew the Covenant to Earth. This would make sense if Regret's fleet came to Earth looking to recover the artifact and knew nothing about the planet itself. While it had been previously revealed that the Covenant knew the location of Earth, it is not known what value they assigned to it. To them, it may have simply been the location of the artifact in Chawla Base, not the human home world.

The Covenant's extensive knowledge of the MAC stations orbiting Earth might be seen as evidence that the Covenant knew the planet was at least occupied by human forces. However, Covenant forces had already encountered such orbital MAC platforms before, over Reach. Recognizing the serious danger these platforms represented, the fleet halted just beyond their firing range and commence boarding and sabotage actions using smaller craft.

Although losses weighed more heavily on the Humans than the Covenant, the UNSC nevertheless fought a successful holding action at New Mombasa. However, it is probable that UNSC High Command deliberately neglected to tell the medium and lower ranks that the Covenant task force was really but a vanguard of a much larger invasion fleet that would surely be imminent now.

According to the Halo Encyclopedia, "the entire population of Earth was cut in half as the First Battle of Earth began." It does not however specify whether it means half of Earth's population were killed, or if a significant number were evacuated.

Trivia

 * Based off the events of Halo 2 and Halo 3 and before the release of additional information in Halo: Ghosts of Onyx and later, Halo 3: ODST, it was assumed that there were two separate Covenant invasions on Earth; Regret's failed invasion on October 20th and later, the arrival of Truth's forces in late November. As newer sources have shown, reinforcements sent by Truth arrived only mere hours after Regret's failed assault. Consequently, this led to classifying the battles as the "First" and "Second" Battles of Earth. This is also the way the battle is listed in the Halo Encyclopedia.