Planetary warfare

Planetary warfare is the conduct of conflict between armed belligerents on the surface of a planet, using land, air and sea-based forces for invading, defending and controlling important strategic areas. Ground warfare varies widely in scale and type, ranging from small skirmishes, to asymmetric combat against nonconventional forces, to large-scale engagements between two or more large forces.

Forerunner Era
Despite possessing powerful spacecraft, the Forerunners and ancient humans continued to deploy ground and air forces in their wars with each other during planetary engagements, the earliest known wars humanity engaged in. The defence of Charrum-Hakkor by combined human and San’Shyuum forces lasted fifty-three years, even after the San’Shyuum leadership surrendered, and included both an orbital defence using advanced Precursor technology and then a brutal ground campaign against Forerunner invaders after those defences fell. Many human and San’Shyuum soldiers chose to commit suicide rather than be captured by the enemy.

After defeating humanity, Forerunner ground forces would face a long, desperate war against the Flood, which depended on planetary engagements to infect and assimilate more victims and increase its capabilities. These engagements invariably ended in a total Flood victory - Forerunner forces eventually resorted to destroying entire star systems, rather than engage them on the ground. While organic Forerunner soldiers proved far too susceptible to infection, towards the end of the war the Forerunners developed sapient machine soldiers to conduct their ground campaigns. However, it was too late to have an effect, and depended on composing too many of the depleted Forerunner Warrior-Servant rate to create their Promethean forces, and the Didact eventually turned to composing humans to try and buy more time, an action that saw the Librarian seal him in a Cryptum on Requiem for his betrayal. Promethean forces would guard Requiem and a number of other Warrior-Servant locations well into the 26th century C.E., long after the activation of the Halo Array.

Post-Activation
In a post-Halo universe, the species returned to their homeworlds developed at different rates. The Sangheili developed an intensely martial culture, and their history has been dominated by a competing system of allied keeps in a constant state of war with each other over resources and old grudges. The species was unified only by their war against the San’Shyuum, where they held the advantage in planetary combat, but the war ended with a stalemate and alliance between the two for mutually beneficial goals, creating the Covenant. The Covenant would encounter many other species during its expansion and exploration of the galaxy, including the Lekgolo and Yanme’e, who would stubbornly resist Covenant intrusion until their assimilation. After their assimilation into the Covenant, the Unggoy’s tensions with the Kig-Yar would boil over into the Unggoy Rebellion, which was fought on numerous fronts across Covenant space, forcing the creation of an Arbiter who threatened to glass Balaho if the Unggoy didn’t lay down arms immediately. Nevertheless, the Sangheili were impressed by the Unggoy’s tenacity, and began conscripting them as soldiers. The Jiralhanae reduced themselves to a pre-industrial state through massive, planetary warfare almost as soon as they had achieved spaceflight, devastating their planet through the use of nuclear weapons, and were ripe for assimilation when they were discovered by the Covenant. The Covenant would have to respond to numerous brushfire rebellions and uprisings during its long history, including the Sixteenth Unggoy Disobedience, and the “heretical” pirate-prince Krith, long before it discovered humanity, which they responded to with military force, often spearheaded by Arbiters created specifically for the task.

Humanity achieved spaceflight much later than most Covenant races, and their history is marked by numerous wars which were exclusively fought on the land, in the air, and on the sea until the development of spacecraft and early colonisation of the solar system. The industrial revolution made the production of highly effective firearms in large numbers cheaper, and marked the end of horse-mounted cavalry and archer volleys. The Interplanetary Wars of the 23rd century were fought in a number of theatres across the solar system: the Jovian Moons campaign on the moons of Jupiter; the Rainforest Wars on Earth; and the Argyre Planitia campaign on Mars. The end of the war would see the unification of Earth’s nations into a single planetary body, the Unified Earth Government, and the creation of the united Nations Space Command. Humanity would subsequently experience a period of peace until the late 25th century, as colonial resentment at exploitation by wealthy Inner Colonies bubbled over into massive and widespread planetary uprisings against Earth rule. While occasionally fought in space, the Insurrection would largely be fought on the surface of the worlds involved, involving prolonged counter-insurgency operations and military occupations in areas recaptured from Insurrection control, with strong air and orbital support.

The Human-Covenant War
The Human-Covenant War brought a screeching halt to most Insurrection activity, though small, stubborn cells would continue to cause the UNSC headaches through the conflict. On the whole, though, humanity as a whole had to contend with the military juggernaut of a technologically advanced, numerically superior, previously unknown alien hegemony that embarked, in 2525, on a war of total extermination against the human species for religious reasons. While the UNSC was heavily outmatched in space, human forces tended to fare much better on the ground against Covenant infantry, armored fighting vehicles and aircraft, though the Covenant’s sheer numbers still tended to overwhelm human planetary forces. Even when the UNSC could score decisive victories on a planet’s surface, the overwhelming technological advantage the Covenant had in space meant that these were usually short-lived, buying time for the UNSC Navy to evacuate as many civilians as they could before the plasma bombardment. The Fall of Reach marked the second-largest campaign of the conflict, and the most devastating one for the Covenant, which lost a considerable portion of the forces it deployed to conquer the planet through heavy human resistance, including widespread Spartan deployments across the planet. The largest campaign would be the Battle of Earth, which saw humanity’s space forces smashed early in the conflict, and the invasion of several locations across the planet before the Covenant withdrew to occupy East Africa. Battles would also be fought on the surface of several artificial planets: UNSC forces from the Spirit of Fire would fight the Covenant on Shield World 9458 in 2531; the Covenant would fight resistance forces from the UNSC Pillar of Autumn in September, 2552 on the surface of Alpha Halo, and later escaped Flood forces; the UNSC In Amber Clad would follow a Covenant Assault Carrier from Earth to Delta Halo, deploying its forces on its surface to secure the Activation Index and assassinate the Prophet of Regret; and after a tentative alliance, UNSC and Sangheili forces would pursue the Prophet of Truth’s forces through a Forerunner portal in East Africa to The Ark, where UNSC ground forces secured a Cartographer facility to locate the Installation’s Control Room, and a combined human-Sangheili strike killed the Prophet of Truth, ending the war.

Though the Covenant would fall apart in the absence of a coherent leadership, numerous factions would continue fighting against humanity and other former Covenant factions. Sanghelios fell into civil war in 2555 with a massive and prolonged uprising against the Arbiter by Sangheili traditionalists across the planet, supported by orbital forces, and the UNSC would fight planetary campaigns against this resurgent Covenant on Draethus V, Requiem, and a number of smaller engagements on small Outer Colonies. These conflicts would see the return of Forerunner Prometheans to galactic prominence, deployed by the Didact on Requiem and subsequently allied to the Covenant after his defeat over Earth, engaging Spartan forces on Requiem’s inner surface during the UNSC’s campaign to secure the artificial planet for the UNSC. The Covenant would face a major setback during the Battle of Kamchatka when Spartan Fireteam Osiris assassinated their leader, Jul ‘Mdama, and the Sangheili civil war would end with the Arbiter’s victory, with the assistance of Osiris, during the Battle of Nuusra and the Battle of Sunaion.

Forerunner
The Forerunners primarily fought their wars using powerful starships, but did deploy forces in planetary environments when they had to, consisting of infantry who used Combat Skins of various tiers, equipped with a variety of handheld firearms, automated support in the form of Sentinels and Armigers, and powerful and agile air support provided by weapon-ships controlled by remote operators. Forerunner forces were at least on par with ancient human forces, and were able to engage them on a roughly equal footing, but had considerably more trouble facing the Flood since their own troops would fill its ranks, using their own technology and equipment against them. The Forerunners responded by creating the Prometheans that were immune to organic infection, using composed Warrior-Servants and unwilling humans to provide them with sophisticated artificial intelligence.

Flood
The Flood is primarily dependent on the capabilities of its enemies to supplement its own. Any living compatant it infects provides with intel and whatever equipment and expertise it possessed when it was assimilated, which is then shared by the Flood hivemind. The physical remnants of its victims become combat forms, serving as basic infantry, until the infection process allows the Flood to begin crafting them into more specialised forms. Infection forms are the primary agent of infection, though in later stages the Flood begins converting local atmosphere to be more hospitable, and releases spores into the air.

Covenant
The Covenant have a very simply policy when it comes to ground warfare: total victory, at any cost. While possess superior technology to the UNSC, and superior numbers, Covenant commanders tend to be wasteful of their troops. Unggoy infantry are particularly considered expendable, and often sent against suicidal odds to overwhelm human defenders, or at the least distract them from Sangheili flanking. Kig-Yar mercenaries are employed, often serving as scouts equipped with wrist-mounted shields, or as sharpshooters. While Yanme’e were only introduced into combat roles late into the war, and were lightly armed and rarely armored, they provided effective air support for allies, harassing human forces from the air while dodging incoming fire. While technically considered infantry, Mgalekgolo are equipped with devastating fuel rod cannons, deployed in pairs to support infantry in areas where larger vehicles would be impractical.

Sangheili officers are not original thinkers, tactically or strategically speaking, but they are rarely stupid. Many commanders are capable of using effective strategy and tactics, although most are raised by traditional military doctrine to observe their own honor codes, which demand Sangheili officers to be present in battle to serve with their troops, needlessly endangering the chain of command. Furthermore, the Covenant denote their ranks using a very clear and observable color-coded system that makes officers highly visible. When the Jiralhanae replaced the Sangheili, they began using more brutal tactics in battle, partially to demoralise human forces and partially to satisfy their own more unrestrained violent nature, including eating captives taken in battle, and continued the use of a color-coded tiered rank system. Both Sangheili and Jiralhanae troops use powered armor that features energy shields, providing limited protection against firearms. While the Covenant typically rely on massed infantry, they also deploy a range of other military forces, including long-range Wraith mortar tanks, and fast and nimble Banshee fighters to provide air superiority and close air support. Troop transport is provided by well-armed and protected dropships, particularly the Spirit and Phantom models, or by armored, and heavy firepower is provided by a range of massive walkers, ranging from light units like the Locust, to larger units like the infamous Scarab, to rare but extremely large units like the Harvester and Kraken. During planetary conquest, the Covenant often bombard a position with plasma from the air or from orbit, devastating large areas and extremely difficult, though not impossible, to survive.

Human
The UNSC features four major military branches, tasked with different duties: the Army, Air Force, Navy and Marine Corps. The Army and Air Force are primarily deployed in defensive roles, garrisoning colonies and holding recaptured territory, while the Marine Corps is the UNSC’s primary expeditionary branch, supported by the Navy. Since the end of the Human-Covenant War, these four have been joined by a fifth branch: the Spartans, staffed by surgically and cybernetically augmented supersoldiers equipped with powered armor, who have become the UNSC’s elite special forces unit. While humans use technologically inferior equipment to the Covenant or the Forerunner forces they’ve fought, they have relied on superior tactical and strategic ability to make their forces effective. While the average UNSC Marine or Army trooper is generally better armed and trained than the most common Covenant infantry, Unggoy or Kig-Yar, they are less effective against Mgalekgolo, Sangheili or Jiralhanae unless supported by UNSC special forces, particularly Orbital Drop Shock Troopers and Spartans. While Spartans were rarely seen during the Human-Covenant War, they have become far more common since, to the point of establishing themselves as their own military branch, on an equal footing with the others. UNSC forces often feature integrated air support and artillery to reinforce infantry or armored units. While the UNSC is capable of fielding extremely powerful armored vehicles, such as the M850 Grizzly, it prefers the tactical flexibility of lighter, highly mobile units such as the M12 Warthog and the M808 and M820 Scorpion tanks which can be transported more easily by dropship. Air support is provided by a variety of VTOLs, helicopters and jet aircraft, and many craft, such as Pelican or Albatross dropships and Broadsword and Longsword fighters, are at home in both atmospheric and vacuum environments, allowing effective orbital support by the UNSC Navy.

The UNSC is not the only military force humanity has by any means. Before its dissolution, the Colonial Military Administration served to enforce Earth’s authority over the Outer Colonies, and was the first military to face the Insurrection before it was subsumed within the UNSC. Many colonies also maintained their own self-defence forces or militias for internal security and disaster relief, often equipped with UNSC surplus military equipment and trained by UNSC advisors. The Insurrection also raised a number of paramilitary forces, using black market or captured weapons, vehicles and ships, though most Insurrection units preferred to operate as guerrilla forces.