UNSC Marine Corps

"We're going in! Get tactical, Marines!"

- Sergeant Major Avery Johnson

The UNSC Marine Corps is branch of the United Nations Space Command Defence Force primarily responsible for land-based military operations, and protecting UNSC Navy starships and bases from attack.

Introduction
A rugged and diverse assortment of warriors, the Marines of the United Nations Space Command Defense Force are fighting a losing war against the Covenant's far superior technology and numbers. Under the leadership of notable commanders, they continue to wage a furious struggle against the Covenant, even as their numbers dwindle. They're the best of the best, unfortunately, they're only Human.

First Encounters


The first documented Marine Corps encounter with the Covenant was the Battle of Harvest, where the UNSC Marine Corps deployed to battle Covenant ground forces on the colony world before it was glassed by the Covenant Fleet. One of the soldiers deployed was Avery J. Johnson.

Another one of their first encounters occured on an arctic world, where the Marine Corps quickly established a home base while an outfit of Marines reconnoitered the nearby area, but were slaughtered by camoflagued Energy Sword-wielding Special Operations Elites. In response, a detachment of Scorpions and Warthogs were sent to investigate, but were too late, and were met, head on, only by a heavy Covenant battle force, with large numbers of Banshee attack fighters and Elite warriors, and the UNSC suffered heavy air casualties. Later, the Marine presence was reinforced by Spartan Group Omega, but the outcome of this battle was unknown.

Battle of Sigma Octanus IV
There was a Marine presence on Sigma Octanus IV. In the first stage of the battle, while the UNSC Destroyer UNSC Iroquois destroyed one Covenant Destroyer and two Covenant Frigates in an ambitious naval tactical manuever, a Covenant Carrier was able to land a large contingent of troops on the northern pole of the planet.

The Covenant were able to take Côte d'Azur, a major population center. Fortunately, almost all of the civilian population was able to be evacuated beforehand, and UNSC Marine Corps General Kits launched an assault by 0700 hours to retake the city. It was unsuccessful.

Meanwhile, three Marine squads, nearby Côte d'Azur and under the command of Lieutenant McCasky, were dispatched for a light reconnaissance of Sigma Octanus IV Grid 13 x 24. They were engaged by Covenant forces, including Hunters, and a sole UNSC M12 Warthog LRV of the reconnaissance force survived with four Marines by the names of Harland, Walker, Fincher, and Cochran. Shortly afterwards, Firebase Bravo was destroyed by the Covenant, and the Warthog was forced to divert to Marine HQ, (Alpha Headquarters). It, too, had been attacked, though the Covenant attack had been repulsed, though not without suffering heavy casualties. Harland promptly requested reinforcements from the Marathon-class Cruiser in orbit, the UNSC Leviathan. The Leviathan sent a team of twelve SPARTAN-IIs commanded by SPARTAN-117 to reinforce.

The surviving Marines of Marine HQ protected a Pelican Dropship while the SPARTANs detonated a HAVOK Nuclear Warhead in Côte d'Azur, cleaning the Covenant ground presence from Sigma Octanus IV, and then retreated back to the Marine-secured Pelican Dropship, which promptly took off with other Pelicans holding other Marine survivors for the UNSC Leviathan.

Battle of Reach
The UNSC Marine Corps maintained a sizeable presence of Reach when the Covenant stormed the planet, bypassing the defense fleet in orbit and landing large numbers of soldiers on the north and south poles. By 0555 hours, the Covenant had overrun FLEETCOM HQ on Reach, destroying the perimeter and swarming the Marine defenders with Banshees, Wraiths, and battalions of infantry. The objective of the Covenant ground armies was to destroy a series of fusion reactors on Reach's surface that powered the orbiting Super Magnetic Accelerator Cannon-equipped Orbital Defense Platforms, and thus, disabling the UNSC's sole major defensive asset and allowing the Covenant fleet to occupy Reach's airspace.

By 0622 hours, the situation was critical enough that the UNSC Halycon-class Cruiser sent a full detachment of SPARTAN-II supersoldiers to Reach in a Pelican Dropship to defend the fusion generators. The Orbital Defense Platforms were already being vaporized in space, and if they were compromised from the ground, the meager remaining UNSC defense fleet would swiftly fall.

Meanwhile, Charlie Company, a Marine detachment, was charge of defending Orbital Defense Generator Facility A-331. They were forced to defend against a massive Covenant attack, using chainguns and missiles to fight off superior forces. Lieutenant Buckman, the CO of Charlie Company, flanked the Covenant, but FLEETCOM was alarmed that the Covenant overrun ODG A-331, and bombed the area, eliminating the Covenant as well as most of Charlie Company.

There were four survivors of Charlie Company that held their position until they met with the SPARTANs. The survivors were sent with several heavily wounded SPARTANs to a fallback position at Mechanite Mountain, but all four Marines died from the Covenant, ending the UNSC Marine Corps's involvement in the Battle of Reach.

Landfall
A sizable Orbital Drop Shock Trooper special forces detachment and a standard Marine detachment was assigned to the UNSC Pillar of Autumn for its intended operation to infiltrate Covenant High Command and kidnap a Prophet as leverage for negotiating a peace treaty between the UNSC and the Covenant. However, the ambush over Threshold forced the Pillar of Autumn to crash land on the Forerunner installation known as Installation 04 (Alpha Halo). The Pillar of Autumn's ODST detachment consisted of four 130-man companies: Companies A, B, C, and D, for a total of approximately 520 operators. During the Covenant boarding of the Pillar of Autumn, they were assigned to defend the engine room of the warship against the boarding parties. They were extremely efficient in their defense, suffering only several dozen casualties while successfully holding off the Covenant at the two entrances to the massive engine chamber. However, the standard Marines did not fare as well in their defense, setting up multiple lines of defense around the periphery of the Pillar of Autumn and utilizing Combat Barriers and urban combat techniques in the restrictive environment to hold off the enemy Elites, Hunters, Jackals, and Grunts. Ultimately, they were unsuccessful, and the Covenant were able to infiltrate many compartments of the warship before Captain Jacob Keyes, commander of the Pillar of Autumn, decided it was a lost cause to hold off superior numbers of attacking Covenant warships as well as internal boarders and ordered all hands to evacuate. .

Naval crewmen and standard Marines evacuated in Bumblebee lifepods while the ODST companies utilized Human Entry Vehicles. The landings, however, had numerous problems and killed dozens of UNSC soldiers and crewmen alike. Major Antonio Silva, the ODST Commander, ordered all surviving ODST units to secure a lightly-defended Covenant-held butte, which he turned into a coordinating home base for the UNSC resistance to come against the Covenant. After securing it, the ODSTs worked to make it a strategically defendable point for the UNSC survivors. It was christened Alpha Base, and Major Silva ordered all remaining UNSC forces to rendezvous there to make a stand. The Covenant launched a large vehicular raid on Alpha Base of nearly a hundred Ghosts, but the 500 or so remaining ODSTs were able to repulse the poorly led assault.

The Covenant placed as high a priority on recovering UNSC lifepods as the UNSC forces did. Many of the successful landings were soon sieged by Covenant attacks in an effort to minimize the number of UNSC personnel on the ringworld. Individuals and teams such as SPARTAN-117's group spent a considerable amount of time securing lifepods throughout the installation. However, it was soon learnt that Captain Jacob Keyes had been captured by the Covenant.

Truth and Reconciliation
SPARTAN-117 led Fire Team Charlie to rescue Keyes from the grounded Covenant CCS-class Battlecruiser Truth and Reconciliation. They would set down a short distance from the Covenant battlecruiser, and then infiltrate through its Gravity Lift. From there, they would find Keyes, rescue him, and then evacuate.

Surprisingly, the plan went almost flawlessly. Despite a pair of Hunters being deployed by the Gravity Lift, the approach was simple. From there, they were able to go up the Gravity Lift into the belly of the Truth and Reconciliation. The UNSC forces tenaciously fought their way through alien corridors for fifteen minutes before reaching a spacious hangar bay. However, before they could continue, the Covenant were able to lock the doors on the Marines and the Master Chief, continually sending in waves of reinforcements to kill the trapped UNSC soldiers in the locked hangar bay. After losing a significant amount of soldiers, Cortana was able to use her computer countermeasures to force open a door that lead from the hangar to the bridge of the warship. SPARTAN-117 ordered his Marine comrades to wait in the bridge while he assaulted a Covenant brig, freeing Keyes and also three other captured Marines. However, by the time they returned to the bridge, Energy Sword-wielding Elites had slain the rest of the recuse team. They headed to the Hanger Bay for evacuation, but Covenant air patrols prevented their rescue. Instead, the team chose to hijack an enemy Spirit dropship that was laying dormant in the hangar bay, with Captain Keyes freed and secured.

Shortly afterwards, the UNSC Marine forces stationed at Alpha Base, under the judgment of Major Silva, decide to embark on a risky raid on the crashed hulk of the Pillar of Autumn to get much-needed supplies and ammunition, vehicular support, and fuel for the ferrying Pelican Dropships. A small ODST force under the leadership of Lieutenant McKay raided the Covenant-patrolled crash site of the Pillar of Autumn, using sniper fire to eliminate most of the defending Ghost attack vehicles and infantry, and then securing the ship with minimal difficulties, securing supplies for the UNSC forces. However, the Covenant learned about this, and before McKay's force can return to Alpha Base and drop off the newly-seized supplies and vehicles that they had secured from the wreck of the Pillar of Autumn, they were intercepted by a superior Covenant force in a rocky terrain. The tide of battle is turned to the UNSC's favor, however, by discipline, organization, and luck. The UNSC's four Scorpion Tanks used shell bombardment to destroy the attacking Covenant Wraiths, while UNSC Warthogs fought off waves of assailing Banshee attack craft and Ghosts. The Covenant's aggressive tactics were no advantage, and the well-coordinated UNSC rocket units and a particularly bold feint by Second Lieutenant Oros destroyed the dozens of Covenant Banshees, and Marine sharpshooter Lance Corporal Jones took a serendipitous sniper rifle shot, killing a Covenant Elite officer, disorienting and fragmenting the Covenant resistance as UNSC forces plowed through the Covenant remnants. .

The Flood
"Ahh... augh! Get it off! Get it-augh!"

- Private Riley, first UNSC casualty to the Flood

Meanwhile, a Covenant Elite, 'Qualomee, surrendered to the UNSC and yielded intelligence about a Covenant arms cache in a faraway swamp. After Captain Keyes meets Major Silva and congratulates him and his ODST special forces operators for establishing Alpha Base for the UNSC, Keyes decides to lead a team of two squads of Marines under the leadership of Sergeant Avery J. Johnson to secure this Covenant arms cache while SPARTAN-117 is ordered to a remote island where a Forerunner construct named the "Silent Cartographer" is stationed - a construct that is believed to hold an entire and fully-detailed map of Installation 04. Securing the intelligence would give the UNSC an inestimable edge in their resistance efforts. Two Pelican Dropships inserted two squads of Marines (lead by Gunnery Sergeant Waller) and SPARTAN-117 to an edge of the island. They were deployed under fire, but managed to secure a beachhead and a landing zone for the UNSC to land further reinforcements (including an M12 Warthog LRV). SPARTAN-117 and two Marines, Hosky and an unnamed Marine corporal, took the Warthog, driving it to a cliff that was the entrance to the facility that housed the Silent Cartographer. However, the Covenant knew that the UNSC was attempting to secure the intelligence, and locked the entranceway, forcing the trio to make a detour to a security substation, deactivating the locked door before finally being able to tunnel their way through the Covenant defenses stationed inside the subterranean facility and retrieving the intelligence.

The surviving Marines still awaiting on the landing zone were scheduled to be reinforced by Pelican Bravo 22 when it was shot down by ground fire. Shortly afterwards, a pair of Spirit dropships converged on the Marines by the landing zone, slaughtering them all on the exposed terrain of the beachhead while SPARTAN-117 was still within the bowels of the underground facility. The lack of a UNSC-held landing zone on the surface of the island meant that Echo 419 could not extract SPARTAN-117 and his vital intelligence. However, Cortana finds that there is a massively honeycombed system of massive open corridors that permeate the ground of Installation 04, allowing a vehicle that entered the system to travel essentially anywhere undetected. Echo 419 is able to slip into the system and rescue SPARTAN-117. Using this system, SPARTAN-117 was able to be transported to the installation's Control Room.

Captain Keyes's team, meanwhile, landed near the site of the supposed weapons cache. The two Marine teams cleared the Covenant defenses and began to search the underground facility where the arms were supposedly stored. One team stayed back while the other team, led by Sergeant Johnson, searched the facility. Eventually, they ran across a door that had been electronically locked by the Covenant. Keyes ordered the door be opened. Shortly after entering the room, however, the advance team, including Captain Keyes, weas attacked by the Flood. Sergeant Johnson would be left to play dead as Flood Infection Forms took over his fellow soldiers as his body was unsuited for infection. Private Jenkins would also survive the attack due to a failed infection attempt and was rescued by UNSC forces.

Cortana had already learnt of the threat the Flood possessed and sent SPARTAN-117 to save Keyes. However, the Spartan would only find Jenkins' helmet and it's mission log. When he finally evacuated, he ran into several Marines and began retreating with them. He would then disappear after encountering 343 Guilty Spark. .

Meanwhile, Alpha Base came under heavy attack from a Covenant force. The Covenant had identified that SPARTAN-117 was responsible for the majority of the hundreds of casualties during the raid on the Truth and Reconciliation, and an ambitious Special Operations Elite named Zuka 'Zamamee was tasked with leading a platoon of Special Operations Elites into the bowel of Alpha Base to assassinate the SPARTAN-II while a much larger Covenant force distracted the UNSC defenders. Using a captured Pelican dropship, Charlie 217, 'Zamamee infiltrates the UNSC HQ, but SPARTAN-117 is nowhere to be found. Meanwhile, Spirit dropships hit the UNSC defenses hard, but are repulsed by mass sniper rifle fire and several Scorpion Tanks. Furthermore, the ODSTs organize several hunter-killer teams to re-secure the HQ, murdering all the Special Operations Elites save 'Zamamee, who is able to rescue a UNSC-captured grunt named Yayap and escape with Yayap in a Banshee fighter.

Containment
While SPARTAN-117 journeyed through various areas in Installation 04, Cortana was able to briefly contact Alpha Base, informing them that SPARTAN-117 will use the Pillar of Autumn's fusion reactors to trigger a thermonuclear explosion that would destroy Installation 04. However, the explosion would kill all life on the ringworld if the UNSC forces failed to escape before the detonation. Major Silva came up with an audacious plan: to recapture the damaged Truth and Reconciliation, already taken to launch readiness by a Covenant repair team, and to use it to escape the ring while SPARTAN-117 sets off the delayed thermonuclear reaction and escapes as well. Afterwards, SPARTAN-117 will rendezvous with the UNSC-controlled Truth and Reconciliation and then they will return to Earth, heralding a glorious victory for the UNSC: a superweapon destroyed, a Covenant armada annihilated, and the first Covenant warship ever captured.

However, the plan was not perfect. Alpha Base's contingent learned of the Flood as a brief skirmish with nearby Covenant patrols leads to an exaggerated battle as the Flood attack, and the UNSC personnel are mostly horrified by the Flood's combat potential and viciousness. After it was learned that Flood are aboard the Truth and Reconciliation, ODST Lieutenant McKay and UNSC AI Wellsley were convinced that the UNSC survivors should not risk severe casualties boarding a Flood-held starship...and even if they prevail and bring the warship to Earth, if any Flood managed to invade Earth, it would "fall". However, Silva, the commanding officer of all of Alpha Base's forces after Keyes's untimely death, demurs, and instead assaults the Truth and Reconciliation, with his ODST special forces operators securing the ship with minimal casualties and the noncombat personnel in tow. Surviving senior naval officers from the Pillar of Autumn are sent in after the ODSTs deem the warship as "secure", and they move swiftly to undersee last-minute repairs to the Truth and Reconciliation before it takes off.

However, McKay still holds doubt - even if the Truth and Reconciliation took off successfully and reached Earth without incidence, the epidemiological threat of the Flood meant that if even one parasite managed to infect a human on Earth, it would be a disaster of a galactic scale. McKay, in conscience, is forced to damage the Truth and Reconciliation's reactors and destroy the warship, killing herself and all the UNSC personnel and surviving Flood beings onboard.

Escape
While almost all of Alpha Base's personnel are eliminated in the tragic self-detonation, Avery J. Johnson did not make it onto the Truth and Reconciliation after surviving the Flood attack. He was able to join three other UNSC personnel that were, likewise, not aboard the Truth and Reconciliation as well: Office of Naval Intelligence Lieutenant Elias Haverson, ODST Corporal Locklear, and Warrant Officer Sheila Polaski. Together, the four escaped Installation 04 in a Pelican Dropship before SPARTAN-117 set off the thermonuclear detonation, himself escaping in a C709 Longsword-class Starfighter.

After Installation 04's destruction, Cortana conducted a scan of the interstellar debris of Installation 04, and found an echo of Polaski's dropship. SPARTAN-117 was able to link up with the four other UNSC survivors of the cataclysm, but seven Covenant warships: six Covenant Cruisers and one 3-kilometer Covenant Flagship, entered the system and opened fire at the fighter and the Pelican. SPARTAN-117 ordered everyone into the Longsword while the Pelican was sent ahead as bait, drawing plasma fire from the Covenant starships while Cortana remotely hacked into the Covenant taskforce's Battlenet, causing electronic mayhem that temporarily stunned the weapons aboard the warships while the Longsword, with SPARTAN-117, Johnson, Locklear, Polaski, and Haverson on board, slipped into the hangar of the Covenant Flagship. The small group of unprepared UNSC warriors fight through Elite defenders while Cortana slips into the Covenant Flagship's computer systems from a fiber optic port, and then proceeds to drain atmosphere from most segments of the ship, asphyxiating most of the Covenant guards. However, the bridge's crew still remains oxygenated, and seal the doors to the bridge, barricading themselves from the UNSC raiders. This measure is futile: SPARTAN-117 uses a plasma grenade to electromagnetically scramble the locks to the doors, and the UNSC forces seize the understaffed bridge with minor difficulties...SPARTAN-117's personal energy shields fail just as an Energy Sword-wielding Zealot appears. SPARTAN-117 is severely wounded in the resulting wrestle, but Marines Johnson and Locklear are able to kill the Zealot.

Cortana interfaces with the bridge's navigational controls to let the now UNSC-controlled flagship, Ascendant Justice, flee from the system, but a Covenant AI counters her, physically disabling the Slipspace drive of the Ascendant Justice and preventing Cortana from executing a jump out of the system before the six other Covenant Cruisers vaporize the flagship. SPARTAN-117, however, makes a journey through the damaged warship to kill the Grunts guarding the disabled Slipspace drive, and then forces a Covenant Engineer to repair the drive, allowing Cortana to program the Ascendant Justice to jump from the system, barely surviving the bombardment of the six Covenant Cruisers, thus ending the UNSC retreat from the wartorn system.

First Battle of Earth
"We're taking this fight to the surface."

- Commander Miranda Keyes

The UNSC Marine Corps remained in large force on Earth and its geosynchronous Orbital Defense Platforms, and were thus mostly prepared repulse a Covenant invasion when fifteen Covenant capital warships - Assault Carriers and thirteen Covenant Cruisers - invaded the Sol System.

Because the large number of orbital Magnetic Accelerator Cannons made it almost impossible for any of the Covenant warships to reach Earth unscathed, the Covenant sent boarding craft to board a number of Orbital Defense Platforms. The boarders were to swiftly penetrate the platform's infantry defenders and set bombs in the core of the stations and then detonate them, destroying the defense station inside-out with minimal losses. Malta Station and Athens Station fell almost immediately to the internal sabotaging, and Covenant forces invaded Cairo Station as well, the command center for UNSC fleet operations during the battle. The crew of the Cairo held out longer, ableit with heavy casualties, and Marines and crewmen fought a coordinated holding action, trying to force the boarders out of the peripheral hangars and the intermediate common rooms, but their defenses were penetrated by a small force of Elites and Grunts that planted a bomb in the Fire Control Center of Cairo Station. Only SPARTAN-117's timely reinforcement of the Marine garrison and his assault on the Fire Control Center managed to disarm the bomb in time, thus saving Cairo Station from destruction.

However, despite the fact that Cairo Station and hundreds of others of Orbital Defense Platforms still stood, the loss of the Malta and Athens allowed a Covenant Assault Carrier to penetrate the UNSC Navy's defensive web around Earth, and this Assault Carrier attacked Mombasa, Africa. However, the 405th Marine Infantry Division, some of whose elements were stationed at Mombasa at the time, were able to battle against the Covenant as the Assault Carrier landed Phantoms, Orbital Insertion Pods, and used its Gravity Lift to directly deploy reinforcements. Furthermore, the UNSC In Amber Clad was also able to use its Pelicans to deploy Marines to assist the 405th Marine Division.

The In Amber Clad sent three Pelican Dropships to reinforce and to drop off Marine and ODST fireteams at Grid Kilo 23, where SPARTAN-117 would lead a coordinated Marine assault to liberate the Covenant-contested city center, when the Pelicans were unexpectedly attacked by a Scarab walker en route. Two of the Pelicans were forced to break off when one of the In Amber Clad's Pelicans, which contained SPARTAN-117 and Sergeant Johnson, crashed into a building. Miraculously, everyone aboard the Pelican save the pilot survived, and SPARTAN-117 was able to rally the Marine passengers, holding a nearby battle-damaged building against multiple Covenant attacks until the Marines could be evacuated at a nearby clearing. SPARTAN-117 meanwhile proceeded to liberate a small ODST force, under Gunnery Sergeant Pete Stacker, at Hotel Zanzibar, and then fought through a Covenant-controlled tunneled highway. Meanwhile, a Covenant Scarab walker brushed aside Marine defenses, walking over the highway, and then past a large bridge and into the midsections of the city completely unopposed by Marine small arms fire.

SPARTAN-117 and a small team of Marines pursued the lumbering walker, fighting through long segments of Covenant-controlled city locations until reaching the city center, where "A" Company of the 405th Marine Division defended against waves of Covenant Ghosts, Wraiths, and Phantoms in a fortified industrial building. Completely undeterred by UNSC Marine Corps Scorpion Tanks or .50-caliber machine guns, the Scarab too brushed aside "A" Company in its fortified building, until it was caught in a nearby canal system and physically trapped. Pelicans commenced air strikes on the trapped walker, but the armor was barely scarred, and there was no other choice but to board the Scarab itself and destroy internally. While "A" Company's remnants provided suppressive fire, SPARTAN-117 jumped aboard the enemy walker, killing its crew and destroying it.

Battle of Installation 05
"This...is another Halo."

- Cortana

"So this is what my father found..."

- Commander Miranda Keyes

After the Slipspace cataclysm over New Mombasa involving the Prophet of Regret's Assault Carrier, the UNSC Frigate UNSC In Amber Clad pursued the Prophet of Regret's carrier through Slipspace to Installation 05 (Delta Halo), where Regret was determined to sermonize and then activate the ring world and bring about The Great Journey to all of the Covenant and lead them to a believed transcendence. While the carrier sent Phantom dropships to the surface to land a Covenant army on Installation 05 and to allow Regret to begin his religious ceremony in a Forerunner temple before activating the ring, the In Amber Clad passed over the approximate position where Regret's temple was, deploying ten Human Entry Vehicles, and shortly afterwards, a group of Pelican Dropships.

While only a handful of HEV pods survived the insertion, the surviving ones contained SPARTAN-117 and several heavily armed Orbital Drop Shock Troopers. Together, they cleared a small area of Shielded Plasma Cannons and a small group of Covenant soldiers, establishing an LZ for a Pelican Dropship to deploy an M12 Warthog LRV and another pair of ODST operators. SPARTAN-117 took the Warthog, and with the help of the ODSTs, fought through a Covenant-controlled bridge before another Pelican deployed a Scorpion Tank that provided extra firepower for a UNSC offensive to push through two large Forerunner temple ruins, where yet a third Pelican from the In Amber Clad dropped off ammunition-resupplying Resupply Canisters and Marine reinforcements. After battling through a rivered ravine entrenched by aerial Drones and Jackal Snipers, the UNSC force reached a small Forerunner temple, where SPARTAN-117 and two remaining Marines fought off a pair of Honor Guard Elites before continuing onwards through a series of closed temples before reaching an open circular platform where a fourth Pelican was scheduled to air-drop additional armaments. However, before that could happen, SPARTAN-117 and whatever surviving Marines were attacked by an airborne Phantom dropship that deployed two heavy Hunter warriors that savagely assailed the UNSC personnel before they were fought off and the fourth Pelican arrived to bring BR55 Battle Rifles, Sniper Rifles, and M19 SSM Rocket Launchers. SPARTAN-117 continued to take a gravitic gondola from the open platform, fighting off enemy Banshee fighters and Ranger Elites to reach a series of submerged temple structures and finally another gondola to the temple where Regret was sermonizing, and fighting off Energy Sword-armed Honor Guard Elites, managed to assassinate the Prophet of Regret before the Prophet of Truth and Prophet of Mercy ordered an Assault Carrier to use an Energy Projector to vaporize the temple in a vain attempt to kill the "Demon", afterwards which contact was lost with SPARTAN-117 and whatever remaining Marines that were accompanying him at the time.

Meanwhile, at High Charity, the Changing of the Guard occured, and the Arbiter was deployed to the Sentinel Wall to deactivate the containment shield that prevented any being from journeying to the Library and retrieving the Index. After the Containment Shield was deactivated, appearantly several Marines were sent to the Flood-Infested Wall to try to make their way to the Library, but were overwhelmed by the Flood and assimilated. However, while the Arbiter punched through heavy Flood defenses surrounding the Library, the UNSC tried again to attack the Library and secure the Index to ensure that the Covenant would not use it to activate Installation 05 and cleanse the galaxy of sentient life in their misguided religious quest. While the Arbiter cleaned out the Flood infestation barring way to the Library, the UNSC were able to slip a small force of Marines directly next to the Forerunner structure, who managed to infiltrate it, but took casualties from Flood infection forms. Corporal Perez, and McKenzie, both UNSC Marines, died from infection forms at the periphery of the Library. At the end, only Miranda Keyes and Avery Johnson survived, but while Commander Keyes secured the Index, the Arbiter managed to race into the Library, incapacitating Perez and MacKenzie before launching a sneak attack on Johnson and Keyes, knocking them both unconscious before securing the Index for the Covenant.


 * See the main article: Battle of High Charity

However, SPARTAN-117 had survived the Covenant vaporization of Regret's Temple, but had a more insidious fate: decieved by the Flood overlord creature known as the Gravemind, he became the Flood's pawn, being teleported to High Charity in an attempt to battle through legions of Covenant troops to capture or kill the Prophet of Truth and secure the Index to ensure that Truth would not activate Halo. Early on during the Battle of High Charity, however, Cortana detected the CNI wave signatures of several UNSC Marines inside the bowels of High Charity. SPARTAN-117 took a short detour, launching an attack on a four-story Covenant detention facility and rescuing five UNSC Marines from a pair of heavily guarded Covenant detention blocks, who aided him in his battles through High Charity. In the end, however, none of the five survived, and the Prophet of Truth escaped from SPARTAN-117's grasp, fleeing in a Phantom dropship while Tartarus, Chieftain of the Brutes, took the imprisoned Keyes and Johnson, along with a cohort of Honor Guard Brutes, in two seperate Phantoms to Installation 05, where Tartarus planned to use the Index to activate Halo at the Control Room of Installation 05.

Meanwhile, the In Amber Clad had not fared well after Keyes's team's departure from the frigate. Flood forces managed to storm aboard by unknown means, killing the human crew and using their unprecedented sentience to crew the ship, managing it to crash it onto a high tower on High Charity, spreading Flood into the Covenant planetoid, and also crew its Pelican dropships, which also scattered and crashed, providing the Flood with extensive routes to invade High Charity. A number of its crew were assimilated into the insula of the parasite, fighting against SPARTAN-117 as the Master Chief battled through a Flood-infested High Charity to secure access to the Forerunner Ship.

While Tartarus took the Index and Miranda Keyes in one Phantom to the Control Room, the other Phantom, carrying Johnson, diverted its route...when Johnson appearantly managed to overpower the Brute crew and escape the Phantom, managing to slip through to an inactive Scarab walker while two nearby Marines fought off a large pack of Brute Captains with Plasma Pistols. These two Marines were saved when the Arbiter arrived, slaying the Brutes. However, Johnson pointed the Scarab's main cannon at the Arbiter...but not in bad will. The Arbiter and Johnson made a truce. Johnson would use the main cannon of the Scarab to punch a hole in the surface of the Control Room while the Arbiter would charge in with a Banshee and defeat Brute Captains and Brute Honor Guards before confronting Tartarus while Johnson would unmount from the Scarab, joining a large number of Covenant Seperatist Councilors, Zealots, and Special Operation Elites in aiding the Arbiter to kill Tartarus and prevent him from using the Index to activate Halo.

However, Tartarus put up a significant resistance, and despite being heavily outnumbered by the Arbiter's Elite comrades, used his personal energy shield and the gargantuan Hammer of Rukt to defend himself. In the end, however, Tartarus was unsuccessful. Johnson used his exceptional marksmanship with a sniper rifle to take down Tartarus's powerful shields from afar with a Particle Beam Rifle while the Arbiter and his allies attacked the unshielded Tartarus, finally killing him and bringing an end to the Chieftain of the Brutes and preventing the firing of the Halos, terminating the UNSC Marine Corps's involvement at Installation 05.

Second Battle of Earth
The UNSC Marine Corps had a substantial involvement in the defense of Earth during the Second Battle of Earth, being the majority of the UNSC's ground defenses when the Covenant landed on Earth in multiple locations, which included the continent of Africa.

A scattered Marine presence appeared to remain in force in the immediate vicinity of New Mombasa, where a Slipspace disaster wiped off a significant number of Marine assets, including at least a portion of the 405th Marine Infantry Division. A number of Marines were present in an African jungle, where they aided SPARTAN-117's mission to destroy a nestled Covenant Loyalist encampment. Later, after SPARTAN-117 broke out into a UNSC base on the outskirts of Voi, he was dispatched with a pair of Marine-crewed Mongooses to punch through Covenant Loyalist blockades in New Mombasa and Tsavo Highway and reach the cliffs of the excavation site of the Ark, and was aided by Warthogs.

Afterwards, the UNSC sent a Warthog convoy to Voi, reinforcing the weak UNSC forces there and to penetrate Covenant anti-aircraft defenses patrolling the outskirts of the Ark. First, SPARTAN-117 and a dozen Marines loaded in Mongooses moved to destroy a lumbering Covenant Scarab walker in the area, with the aid of Banshee and Hornet aerial vehicles, and then, with the Arbiter, destroyed a Covenant anti-air emplacement that was heavily guarded by Brutes and Hunters, and allowed a corridor for Miranda Keyes to journey to the heart of the Ark in a Pelican Dropship, unimpeded by anti-aircraft weaponry.

Armor


Marines have few bio-augmentations and usually wear passively camouflaged armored uniforms. They wear dark-colored metal-alloy armor to shield them from gunfire. Marine helmets are mounted with display holographic text-displaying eyepieces and helmet recorders. As well as helmets, Marines on field operations in more humid locales sometimes choose to wear boonie covers, or those in colder environments don visored and thicker helmets.

Marine NCOs are easily recognized by the hat that has the Eagle, Globe and Anchor of the Marine Corps that they wear. They often times substitute this command hat for a protective helmet, although they occasionally wear helmets in Halo 2, although in Halo: Combat Evolved, they are portrayed as always wearing the hat. Sergeants are (usually) more tactically adept, are better shots, and are tougher to kill than normal Marines, though these differences in gameplay, if any, are largely unnoticed.

In Halo: Combat Evolved, Marines sported gray fatigues, and over that, pieces of brown armor plating covering the head, shoulder, and shins. At times, they only wore their fatigues, even forgoing helmets or even body armor plating in hazardous combat operations. At times, their helmets were also subsituted for boonie covers. Some Marines had small backpacks built into their back chest armor plating, although these backpacks appeared to be part of a medical uniform, as the text "EMP" (Emergency Medical Pack) was written on the back.

The UNSC Marine armor was much different in Halo 2. Marines appear to wear an armored suit underneath jungle camoflague-patterned padding, and a conspicuous green load-bearing armored vest over their chest pading for additional protection. The standard-issue armor is more efficient than the body armor issued to the Marines of Halo: Combat Evolved. The Marines apear as less of a rag-tag group in Halo 2 than they were in Halo: Combat Evolved. They no longer wear boonie covers and are never in combat without their armor. In fact, in Halo 2, the only times Marines are seen without any armor is during the awards ceremony aboard Cairo Station during a noncombat situation. In that case, they were wearing their dress whites.

In Halo 3, the Marines sport armor that is an evolution from that of Halo 2, with heavier and well-articulated woodland-colored full body armor (chest plate, back plate, shoulder plates, elbow pads, and knee pads) over camoflagued fatigues, allowing them to passively camoflague well in jungle terrain. Marines sometimes don boom mikes or black-phased sunglasses on their helmets, and others carry backpacks.

Orbital Drop Shock Troopers, otherwise known as "Helljumpers", are a special operations group within the UNSC Marine Corps. They wear full body armor with a dark black camoflague scheme. They sport heavy and articulated black body armor, which is also believed to be pressure armor that allows for safe transport in small ships in turbulent atmospheric entry and also fully-covering and fully-visored black helmets.

Marines operating in cold environments wear environmentally-tailored armor, with snow camoflague scheme heavily thickened and fully-covering body armor and visored helmets with bacaclavas.

Halo: Combat Evolved

 * MA5B ICWS Assault Rifle
 * SRS99C-S2 AM Sniper Rifle
 * M90 Assault Shotgun
 * M41 SSR MAV/AW Rocket Launcher
 * M9 HE-DP Grenade

Halo 2

 * M6C Magnum Sidearm
 * BR55 Battle Rifle
 * M7/Caseless Sub Machine Gun
 * SRS99C-S2 AMB Sniper Rifle
 * M41 SSR MAV/AW Rocket Launcher
 * M90 Assault Shotgun
 * M9 HE-DP Grenade
 * M247 GP Machine Gun

Halo 3

 * M6G Magnum
 * MA5C Assault Rifle
 * BR55HB SR Battle Rifle
 * M7/Caseless Sub Machine Gun
 * W/AV M6 Grindell/Galileian Nonlinear Rifle "Spartan Laser"
 * SRS99D-S2 AM Sniper Rifle
 * M41 SSR MAV/AW Rocket Launcher
 * M90 Assault Shotgun
 * M9 HE-DP Grenade

Halo Wars

 * BR55 Battle Rifle

Halo: Combat Evolved

 * M12 Warthog LRV
 * M808B Scorpion Main Battle Tank
 * D77-TC Pelican

Halo 2

 * M12G1 Warthog LAAV
 * M12 Warthog LRV
 * M808B Scorpion MBT
 * D77-TC Pelican

Halo 3

 * Elephant
 * M274 ULATV Mongoose
 * M12 LRV Warthog
 * Troop Transport Warthog
 * M808 Scorpion MBT
 * D77H-TCI Pelican

Halo Wars

 * M12 LRV Warthog
 * M808 Scorpion MBT

Miscellaneous

 * CH252 Helmet
 * M52B Body Armor
 * VZG7 Armored Boots
 * S90 Gas Mask
 * Spoofer
 * VX7 Nerve gas
 * PG000E Portable Electricity Generator

Halo: Combat Evolved
In Halo: Combat Evolved, almost all Marines carry MA5B Assault Rifles, though occasionally they can be seen with a Sniper Rifle or the Shotgun, or very rarely the Covenant Needler or Plasma Rifle when no UNSC armaments are available. They are relatively accurate with these weapons, with a hit percentage of 50% of upwards, often firing in terse burts with the Assault Rifle, killing a Grunt in one or two bursts, knocking a Jackal's shield of position with repeated bursts, or cooperatively working with other Marines to take down an Elite. Marines also often utilize Fragmentation Grenades in combat.

Marines will strafe and avoid fire but not usually seek cover. They will roll out of the way of a vehicle but they will not pick up different weapons, Health Packs, or additional ammunition. Marines are also good pathfinders, often able to manuever around obstacles such as boulders or fallen crates in their paths.

Marines are conscious of back stabbing. After you have killed two humans of any type, the rest of the Marines in the campaign level will attack the player. If one kills Captain Keyes or any other members of the bridge crew in the campaign level The Pillar of Autumn, Cortana will lock the doors and summon a squad of invincible Marines to destroy one.

Marines hitch rides on player-driven Warthogs and Scorpion Tanks but are only capable of piloting Ghosts by themselves. They will exit Scorpions when the player leaves the driver seat, but will stay in a Warthog until they are ordered to get out.

Interestingly, the enemy Marines are most vulnerable to in Halo: Combat Evolved are the Infection Forms of the Flood. Once one is attached to a Marine, it cannot be shaken off and kills the soldier.

Halo 2
In Halo 2, the Marines are intelligent in different ways than in Halo: Combat Evolved. They are more adept with vehicles, and are able to drive the Warthog, the Ghost, the Wraith, the Spectre, and the Scorpion, albeit a bit clumsily. They can now melee sleeping Grunts or enemies with their backs turned, a vast improvement over the Halo: Combat Evolved Marines, who had to fire their weapons in such situations and ruin operational covertness.

However, their firearm prowess has decreased, and most Marines are unable to achieve greater than a 25%-50% hit percentage with semiautomatic weapons such as the Covenant Carbine, and are instead more effective with close-range weaponry such as the M7/Caseless Submachine Gun or with heavy weaponry such as the M19 Rocket Launcher or the Fuel Rod Cannon. Although their friendly fire incidents are decreased, Marines do not use fragmentation grenades in combat, and are unaware of splash damage from heavy weapons, sometimes firing a rocket into a nearby wall and killing themselves in the operation.

The Marines are far more interactive, sometimes speaking to each other while in combat and wield a greater variety of weapons. The player can also easily switch weapons with the Marines to make sure that they are well armed or that the player is. As in Halo: Combat Evolved, the Marines are aware of backstabbing, and will attempt to kill you after you kill a few of their comrades. The number of Marines that can be killed before the others turn against you oddly seems to vary depending on the weapon used and the way they are shot. For example, taking out three Marines with head shots usually won't make them see you as an enemy, but meleeing three Marines usually does. However, if the player progresses through the level and meets another group of marines a distance away from where the betrayal was performed, they will be marked as allies once again. Also, if the player does not harm any marines who are shooting at him/her for a certain amount of time the Marine(s) will reluctantly return to an allied condition.

Halo 3
It is unknown what the Marines' abilities will be in Halo 3. All that is known about them AI-wise is that they are better drivers and more capable of surviving without the player's aid. Also, when a Marine is manning the turret on the Warthog, the player can tell the Marine where to shoot by repeatedly turning or driving in a specific direction, towards another enemy.

Their audio clips have also been vastly expanded, and profanity is used to indicate critically wounded status.

List of Marines

 * Lance Corporal Janet Adams KIA, Evacuation of Troy
 * Al-Thani KIA, Battle of Installation 04
 * Staff Sergeant Marcus Banks ACTIVE DUTY
 * Private Bisenti KIA, Battle of Installation 04
 * Lieutenant Buckman KIA, Battle of Reach
 * Company Sergeant Tink Carter KIA, Battle of Installation 04
 * Lieutenant Jake Chapman KIA, Battle of Reach
 * Private Cochran ACTIVE DUTY
 * Sergeant Corly KIA, Battle of Installation 04
 * Second Lieutenant Dalu KIA, Battle of Installation 04
 * Dawkins KIA, Battle of Installation 04
 * Private Chipps Dubbo ACTIVE DUTY
 * Major Easley ACTIVE DUTY
 * Corporal C. Errera KIA, Battle of Reach
 * Private Fincher ACTIVE DUTY
 * Private First Class M. Fitzgerald KIA, Battle of Installation 04
 * Lance Corporal Gobi ACTIVE DUTY
 * Corporal Harland ACTIVE DUTY
 * Private First Class Hosky KIA, Battle of Installation 04
 * Private First Class Wallace A. Jenkins KIA, Battle of Installation 04
 * Sergeant Major Avery J. Johnson ACTIVE DUTY
 * Lance Corporal "Snaky" Jones KIA, Battle of Installation 04
 * Private Kappus KIA, Battle of Installation 04
 * General Kits KIA, Battle of Sigma Octanus IV
 * Lindemuth ACTIVE DUTY
 * Master Sergeant Lister KIA, Battle of Installation 04
 * Corporal Locklear KIA, Operation: FIRST STRIKE
 * Corporal Lovik KIA, Battle of Installation 04
 * Second Lieutenant McCasky KIA, Battle of Sigma Octanus IV
 * First Lieutenant Melissa McKay KIA, Battle of Installation 04
 * Private McKenzie ACTIVE DUTY
 * Private Manuel Mendoza KIA, Battle of Installation 04
 * Staff Sergeant Marvin Mobuto KIA, Battle of Installation 04
 * Corporal Benjamin M. Nunez ACTIVE DUTY
 * Private O'Brien KIA, Battle of Installation 04
 * Second Lieutenant Oros KIA, Battle of Installation 04
 * Sergeant Parker KIA, Battle of Installation 04
 * Corporal Perez ACTIVE DUTY
 * Private Marie Postly KIA, Battle of Installation 04
 * Parsons ACTIVE DUTY
 * Private Riley KIA, Battle of Installation 04
 * Private Satha KIA, Battle of Installation 04
 * Major Antonio Silva KIA, Battle of Installation 04
 * Sergeant Stacker KIA, Battle of Installation 04
 * Gunnery Sergeant Pete Stacker ACTIVE DUTY
 * Major General Nicolas Strauss ACTIVE DUTY
 * Private First Class Suzuki KIA, Battle of Installation 04
 * Medic "Doc" Valdez KIA, Battle of Installation 04
 * Private Walker KIA
 * Gunnery Sergeant Waller KIA, Battle of Installation 04
 * Corporal Wilkins KIA, Battle of Installation 04
 * Yutrzenika KIA, Battle of Installation 04
 * LindemuthACTIVE DUTY
 * Unnamed Master Gunnery Sergeant KIA, First Battle of Earth
 * Unnamed Lieutenant KIA, Battle of New Mombasa
 * Unnamed Marine Officer MIA, Battle of Mombasa

Marine Units

 * 405th Marine Infantry Division
 * 17th Marine Regiment
 * 77th Marine Regiment
 * Alpha Company (Battalion unknown)
 * 105th Shock Division
 * 7th ODST Battalion
 * 1st Platoon (Company and Regiment Unknown)
 * 105th Drop Jet Platoon
 * Charlie Company
 * Tango Company

Fire Teams

 * Fire Team Zulu
 * Fire Team Charlie

Trivia

 * In Halo: Combat Evolved, the Marine's faces were modeled on Bungie employees.
 * Bungie went to great lengths to ensure that the Marines reflected the diversity of Earth; some Marines look and sound American, while others appear Asian, African,Australian, Hispanic and Italian.
 * In the Halo: Combat Evolved level "Truth and Reconciliation", Captain Keyes tells a Marine to "Stow your belly aching...! Remember you're a leatherneck." Leatherneck was a nickname earned by U.S. Marines in the 19th century.
 * Rarely, after a Marine is killed in Halo 2, his/her eyes will continue to blink.