UNSC Marine Corps

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

- Staff Sergeant 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.

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.

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, this ending the UNSC Marine Corps's involvement in the Battle of Reach.

Battle of Installation 04
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, in light of the events of the Battle of Reach, the Pillar of Autumn was forced to change its operational plans and 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 warhip before Captain Jacob Keyes, commander of the Pillar of Autumn, decided it was a lost cause to hold off superior numbers of attacking Covenant warhips as well as internal boarders and ordered all hands to evacuate, systemically ordering operations personnel to escape in lifepods while Marine combat teams continued to fall back to secondary defensive positions before Captain Keyes sounded the final evacuation alert.

Naval crewmen and standard Marines evacuated in Bumblebee lifepods while the ODST companies utilized Human Entry Vehicles - low-profile high-risk insertion pods, to evacuate the crashing Pillar of Autumn and land on Installation 04. The landings were in haste and uncoordinated, however, and technological failures and piloting errors killed dozens of UNSC soldiers and crewmen alike. Major Antonio Silva, the ODST Commander, ordered all surviving ODST units to converge on a lightly-defended Covenant-held butte, which he planned to secure and fortify into a coordinating home base for the UNSC resistance to come against the Covenant. The butte was quickly taken, and defensive trenches were dug and ODST commandoes established perimeter security, ensuring that the butte would be a strategically defensive 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 with M19 SSM Rocket Launchers and Sniper Rifles.

Meanwhile, SPARTAN-117, one of the last UNSC soldiers to leave the ship, left in a Bumblebee lifepod, but the lieutenant who was piloting the craft was unable to land the pod safely, and in the ensuing crash landing, SPARTAN-117 was knocked unconscious and the Marines in the pod were killed. However, eventually, SPARTAN-117 awoke, and evaded Covenant patrols, managing to rescue about a dozen Marines that had safely landed in nearby crashed lifepods, defending each of the four groups of Marines until Echo 419 could ferry them back to Alpha Base to join the rest of the UNSC survivors on the ring world.

However, while most of the surviving Marines and naval crewmen were able to call for evacuation by Pelican Dropships after their crash landings, not all were able to be evacuated. Captain Keyes, the senior command staff of the Pillar of Autumn, and several Marine guards, were together in a lifepod and landed without incident when the Covenant recognized that Keyes was the highest-ranking UNSC officer on the ring, and was a major theat. Eventually, Keyes and his senior staffers were captured by the Covenant before they could be evacuated, and all but the captain were executed, and shortly afterwards, Keyes was taken prisoner on a grounded Covenant warship, the CCS-class Battlecruiser Truth and Reconciliation.

After SPARTAN-117 managed to save the survivors of four of the most proximal crashed lifepods, he too was taken back to Alpha Base, but shortly afterwards, after the limited UNSC intelligence efforts revealed that Keyes was a prisoner under interrogation aboard the Truth and Reconciliation, the UNSC resistance sent a small team of Marine regulars (including Fire Team Charlie) and SPARTAN-117 aboard Echo 419 to set down a short distance from the Covenant battlecruiser, and then to infiltrate the ground sentries defending the only accessway into the warship (the Gravity Lift), and to then subsequently find Captain Keyes, rescue him, and evacuate from the Truth and Reconciliation. Surprisingly, the plan went almost flawlessly. SPARTAN-117 was able to use his exceptional marksmanship with the sniper rifle to clear out most of the enemy Shade defense turrets, and then the team of five Marines, lead by Sergeant Parker, was able to follow him in. At the base of the Gravity Lift, there was a large brawl, as Covenant forces were heavily fortified there with Shade turrets. Even after the UNSC raid team neutralized the defenders, the Covenant sent over two waves of reinforcements from a Spirit dropship and sent some of the garrison of the Truth and Reconciliation down the Gravity Lift, including a pair of Hunters that considerably damaged the small UNSC attack force. However, after SPARTAN-117 and the surviving Marines secured the area around the Gravity Lift, Echo 419 air-dropped another team of five reinforcing Marines, and the reinforced UNSC force went 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. With Keyes and the emancipated Marines in tow, SPARTAN-117 treaded back to the bridge, to find his previous Marine allies slain by several Energy Sword-wielding Elites. After defeating them, SPARTAN-117, Keyes, and the freed Marines entered the hangar bay. Echo 419 attempted to dash into the hangar bay to daringly exfiltrate the UNSC force, but Covenant air patrols were too substantial to facilitate that, so the small cluster of UNSC soldiers were forced to hijack an enemy Spirit dropship that was laying dormant in the hangar bay, and used it to escape to Alpha Base, with Captain Keyes freed and secured.

Shortly afterwards, the UNSC Marine forces stationed at Alpha Base, under the judgement 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 raid 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 learn about this, and before McKay's force can return to Alpha Base and drop off the newly-seized supplies and also the UNSC vehicles they secured from the wreck of the Pillar of Autumn, they are 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 use accurate shell bombardment to destroy the attacking Covenant Wraiths, while UNSC Warthogs fight off waves of assailing Banshee attack craft and Ghosts. However, the Covenant's aggressive tactics were no advantage, as well-coordinated UNSC rocket units and a particularily bold feint by Second Lieutenant Oros destroy 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.

Meanwhile, a Covenant Elite, 'Qualomee, surrenders to the UNSC and yields intelligence about a Covenant arms cache in a faraway swamp. After Captain Keyes greets 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 insert two squads of Marines (lead by Gunnery Sergeant Waller) and SPARTAN-117 to an edge of the island. They are deployed under fire, but manage to secure a beachhead and an LZ for the UNSC to land further reinforcements to secure the island and obtain the information from the Silent Cartographer. The surviving Marines establish a perimeter for the LZ while Echo 419 air-drops a 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 SPARTAN-117 to make a detour to a security substation, deactivating the locked door before finally being able to tunnel his way through the Covenant defenses stationed inside the subterranean facility and retrieving the intelligence.

The surviving Marines still awaiting on the LZ are scheduled to be reinforced by Pelican Bravo 22 when it is shot down by ground fire. Shortly afterwards, a pair of Spirit dropships converged on the Marines by the LZ, murdering them all while SPARTAN-117 is still within the bowels of the underground facility. The lack of a UNSC-held LZ on the surface of the island meant that Echo 419 could not exfiltrate SPARTAN-117 and his vital intelligence. However, SPARTAN-117 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. However, instead of being exfiltrated to Alpha Base, SPARTAN-117 reveals that the ringworld is a weapon, a weapon that if secured for the UNSC, could be a tremendous boon to the war effort. According to the Silent Cartographer, the Control Room that coordinates the firing of the weapon is set in a distant snowy environment whose exact coordinates SPARTAN-117 has secured. Echo 419 is able to transport SPARTAN-117 through the massive underground air pathways to a location near this "Control Room".

SPARTAN-117 fights his way through heavy resistance - the Covenant have set up a strong defensive perimeter around the Control Room consisting of Wraith tanks, Ghost attack vehicles, Banshee aerial fighters, Shade turrets, and hundreds of soldiers. UNSC Marine forces, including Fire Team Zulu, are also scattered in the immediate area, and are holding out against superior Covenant forces. SPARTAN-117 rescues each of the Marine fireteams in turn, and then fights up a final hill of entrenched Covenant forces before reaching the Control Room. SPARTAN-117 inserts his armor's Artificial Intelligence, Cortana, into the supercomputer that nests within the room, and inquires Cortana about how Halo can be used as a UNSC-held weapon in the war effort. Cortana, however, does not answer his question, but insists that the supercomputer has written that there is a terrible, menacing, vague "threat" hidden beneath the surface crust of Installation 04, and that Captain Keyes's Marine team's "weapons cache", when "secured", would unleash this insidious enemy. SPARTAN-117 calls for an aerial evacuation from the Control Room, leaving Cortana behind in the Control Room to learn more about the weapons capability of Halo while Echo 419 transports him to the swampy weapons cache that Keyes and his Marine guards travelled to.

However, they are too late. Keyes's strike force of two Marine squads quickly eliminates the weak Covenant defenses, and penetrates into the underground facility that houses the arms cache, with Sergeant Johnson's squad taking point into the structure while the second Marine squad stayed behind in the swamp, with Keyes nestled in Johnson's squad. Eventually, the first Marine squad hits a locked door. The squad's technical specialist, Kappus, uses a Spoofer, an electronic lockbreaker, to open the door. Johnson then orders his Marines to move out into the room beyond and secure it, with Keyes behind them. However, they have not found their arms cache, but instead, have unlocked the galaxy-destroying parasite known as The Flood. Flood Infection Forms overwhelm Johnson's squad and also Keyes, assimilating them as Flood Combat Forms. SPARTAN-117, however, is several hours late. He battles through Covenant defenses outside and inside the facility, before encountering the formerly locked room, and a fallen Marine's combat helmet, with the mission recorder within intact. Viewing the mission recorder, SPARTAN-117 learns that Keyes and the Marines are MIA, and then the Flood attack SPARTAN-117, who defends himself and fights his way out of the facility, with the Flood following him. After he evacuates from the facility, he is greeted in the swamp by the Marines of the second squad, who reported that after they lost contact with Keyes's squad, they headed for the RV point. Echo 419 attempts to evacuate SPARTAN-117 and the second squad to Alpha Base, but they are beset by the Flood, who murder every Marine. Then, SPARTAN-117 meets with the mysterious Forerunner intelligence known as 343 Guilty Spark, who teleports the Master Chief away against his will before Echo 419 can evacuate SPARTAN-117.

Meanwhile, Alpha Base comes under heavy attack from a Covenant force. The Covenant have 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 is 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 distracts 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.

While SPARTAN-117 journeys through various areas in Installation 04, Cortana is able to briefly keep in touch with Alpha Base, logging that SPARTAN-117 will use the Pillar of Autumn's fusion reactors to trigger a thermonuclear explosion that will destroy Installation 04 and prevent it from being use to annihilate sentient life. However, the explosion will kill all life on the ringworld if they do not escape before the detonation, so Major Silva has 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 is not perfect. Alpha Base's contingent learn 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 is learned that Flood are aboard the Truth and Reconciliation, ODST Lieutenant McKay and UNSC AI Wellsley are 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.

While almost all of Alpha Base's personnel are eliminated in the tragic self-detonation, Avery J. Johnson, the Marine Sergeant that lead the disasterous fray into the supposed Covenant arms cache, survived the Flood infection through a pathology called Boren's Syndrome, but did not make it onto the Truth and Reconciliation after surviving the Flood attack...and therefore, not dying in the detonation. However, he was able to join three other UNSC personnel that were not onboard 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 Longsword 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 Pelican, 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.

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.

Equipment
Marines have few bio-augmentations and usually wear passive camouflage uniforms. They wear dark-colored metal-alloy armor to shield them from plasma fire and the few occasional bullets. Marine helmets are mounted with display eyepieces and helmet recorders, which give them information about their surroundings. As well as helmets, Marines on field ops in more humid locales sometimes choose to wear boonie covers. Orbital Drop Shock Troopers or "Helljumpers," distinctive in their black-based camouflage scheme and more protective body armor, are a special operations group within the UNSC Marines Corps.

Marine NCOs are easily recognized by the hat, not helmet, that has the Eagle, Globe and Anchor of the Marine Corps that they wear. They occasionally wear helmets, although in Halo: Combat Evolved, they are portrayed as never wearing them. 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.

The UNSC Marine armor is much different in Halo 2. The utilities worn under the armor are now camouflaged. The standard issue armor is more efficient and is a rough offshoot of the original armor used by Master Chief in 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 on the first level. In this case, they are wearing their dress whites, and one armored Marine is missing the armor for his arms. It should be noted, however, that the full gray Marine armor with additional pockets/backpack in Halo: Combat Evolved was a medical uniform, as suggested by the letters EMP (Emergency Medical Pack) written on the back.

In the Halo Wars trailer, Marines are seen wearing helmets, balaclavas, and environmentally-suited armor to protect them from the cold.

List of equipment

 * 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, Needler, Shotgun, or Plasma Rifle. They are relatively accurate with these weapons, but incidents of friendly fire commonly occur. 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 ammo.

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

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. Be careful of Marines piloting Ghosts. They are occasionally prone to running you over. In Halo: Combat Evolved, the only practical way of getting a Marines' weapon, unfortunately, is by killing them.

Interestingly, the enemy Marines are most vulnerable to in Halo: Combat Evolved are the Infection Forms. The Infection Forms normally appear in overwhelmingly large numbers in the one level where Marines combat them, and cannot be shaken off once attached to a Marine.

Halo 2
In Halo 2, the Marines are much more intelligent. They 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.

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.

They will seek cover behind boxes and walls, though this mainly only happens when the Marines are desperate, so they don't use cover as the player does. Plus, Friendly Fire incidents with standard weapons are very rare. Marines with Rocket Launchers on foot will sometimes kill you, fellow Marines, or themselves by accident.

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. Their armor appears to be metallic like in Halo 1, but with the High-Tec, woodland green armor and camoflauge of Halo 2.

Weapons

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

Vehicles

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

Weapons

 * 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

Vehicles

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

Weapons

 * 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

Vehicles

 * M274 ULATV Mongoose
 * M12G1 LAAV Warthog
 * M12 LRV Warthog
 * M808 Scorpion MBT
 * D77H-TCI Pelican

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
 * 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.