Space warfare is the conduct of conflict between belligerents in space. The scale of space warfare ranges from exoatmospheric fighter skirmishes and boarding actions to battles between fleets of warships, which often decide the outcome of a given engagement or conflict.
Space warfare evolved from engagements on a world's surface or in its atmosphere. With the invention of human space travel in the 20th century, many organizations and nations began to consider or invest in possible military operations conducted in space. In the late 21st century, humanity had become an interplanetary-faring species with colonies established in their home system. The new outlet of travel and exploration would eventually lead to conflict. The dawn of the Interplanetary War and its associated engagements saw the formation of the United Nations Space Command's Navy following the Mars Campaign. The campaign marked a turning-point in space warfare through dedicated utilizations of Marine forces in ground assaults and ship-boarding operations that would follow during the war.
In the late 23rd century, humanity invented and began to utilize the Shaw-Fujikawa Translight Engine on their spacecraft, allowing human ships to travel through slipstream space to reach destinations light-years away. The UNSC Navy only conducted low-level operations, such as anti-piracy actions, until the Insurrection, which forced the Navy to develop a modern space warfare doctrine. Following the Callisto Incident of 2494, the numerous small-scale space engagements occurred between the UNSC Navy and Insurrectionists across human space. While Unified Ground Command (UNICOM) oversees planetary campaigns, orbital defenses and space-based combat is directed by UNSC Naval Command (NAVCOM).
The Covenant races, meanwhile, have been spacefaring for significantly longer than humanity. The Sangheili had been a spacefaring civilization for some time by 938 BCE, when they encountered the San'Shyuum. The resulting conflict was fought on both planetary surfaces and in space engagements, where the San'Shyuum held the distinct advantage due to their use of the Forerunner Dreadnought, a Forerunner keyship fitted by the San'Shyuum with offensive armament. In 1342, the Covenant fought the many Kig-Yar pirate and militia groups around Eayn, including naval engagements against space-based raiders in their homeworld's asteroid belt, where their smaller ships and intimate knowledge of their environment benefited the Kig-Yar until they agreed to be employed by the Covenant. Covenant warships also took part in the glassing of Balaho during the Unggoy Rebellion, though likely faced little serious naval opposition. The Jiralhanae were a spacefaring species, before they were reduced by their First Immolation to a pre-atomic stage, and it is likely that this war included space combat.
As with warfare in general, the level of a given polity's technological advancement plays a considerable role in space engagements, and a technological edge can easily overcome superior tactics once the technological gap is substantial enough. During the Human-Covenant War, UNSC warships and weapon systems were decidedly inferior to their Covenant counterparts. This has changed in the post-war era with the introduction of new, more advanced technologies to UNSC Navy service as well as the Covenant's reduction into various smaller splinter groups with lessened access to the bleeding edge of Covenant technology.
Human starship weapons follow a similar trend as their ground armament and are largely based around ballistic impacts and chemical reactions. Meanwhile, Covenant weapons employ directed energy weapons, such as magnetically-guided superheated plasma, in their various weapon systems, a major contributor to their significant edge over the UNSC during the Human-Covenant War.
Human starship weapons are, for the most part, projectile-based, consisting of guided missiles with variable conventional or nuclear warhead yields or magnetically accelerated unguided projectiles. In combat, UNSC warships employ Magnetic Accelerator Cannons as their primary armaments, powerful coilguns built into the superstructure of the ship capable of accelerating a ferric tungsten shell to a significant fraction of the speed of light. These are supplemented by a range of missile types, from smaller-yield ship-to-ship Archer, Rapier and Howler missiles to more powerful nuclear Hyperion, Rudra, FENRIS, HAVOK or Shiva missiles. UNSC naval strategy emphasizes massed firepower to overwhelm the Covenant's powerful defenses - typically an initial missile salvo to penetrate Covenant point defense, followed up with a timed MAC strike against the vulnerable ship. Single MAC strikes by even smaller UNSC warships are capable of crippling or destroying an unshielded Covenant vessel. The velocity of a MAC round can be adjusted to deliver ordnance from orbit against planetary targets, though the still-powerful kinetic energy they impart on impact means their use is limited. UNSC prowlers are the only known UNSC warship class to use pulse laser turrets, though as stealth ships their primary offensive role is their ability to lay HORNET space mines.
The Covenant, on the other hand, employ more arcane weaponry derived from even more advanced Forerunner technology. The typical offensive armament for a Covenant warship consists of plasma torpedo turrets and energy projectors to engage enemy combatants. Plasma torpedoes are a form of superheated plasma contained and shaped by a magnetic field and guided to the target. While the magnetic field has been created by the ship, plasma torpedoes have been known to continue tracking their targets after the destruction of the warship that launched them. A single plasma torpedo is capable of burning through UNSC hull plating and even through several deck layers in a matter of seconds. Energy projectors are powerful particle accelerators, akin to a larger focus rifle, typically used as long-range armaments. They have been known to cut through even UNSC carriers with little difficulty, but require more power to operate, especially on warships with more than one energy projector. Both of these weapons systems can be used by the Covenant to bombard planetary positions from orbit, in a process known as glassing.
UNSC warships use various forms of Titanium-A armor (an enhanced form of titanium) as their exterior battleplate. Covenant vessels are covered in nanolaminate hull plating, which is significantly stronger and more resilient. Most Covenant ships are further protected by energy shielding, which has seen limited adoption among UNSC Navy warships—including the UNSC Infinity and the Strident-class heavy frigates—in the post-war era. Both sides also make use of point defense weapons, designed to target and destroy singleships and missiles. UNSC ships use a number of different magnetic-accelerator point defense systems, while Covenant point defense is usually performed by more advanced pulse laser turrets. UNSC point defense, among other tasks, is usually handled by onboard ship AIs, capable of performing threat assessment and target designation faster than humans can react. The Covenant have been slower to adopt AIs, due to the example of Mendicant Bias's role in the defeat of the Forerunners by the Flood. Despite this, the Covenant had installed their own versions aboard some warships and the space station Unyielding Hierophant by 2552, though they were of inferior quality to both Forerunner or UNSC AI constructs.
Both the UNSC and the Covenant are known to use dedicated space stations to defend their worlds. UNSC orbital defense platforms are anchored to a geosynchronous orbit and are armed with a powerful "super" MAC gun powered by a groundside generator. Covenant equivalents use versions of the energy projectors used on their warships.
Most space warfare is conducted by warships, supported by resupply ships, fighters and dropships, and space stations that serve as static defenses around planetary orbit. The UNSC Navy designate their ships along similar lines to planetary-based navies. UNSC corvettes are generally the fastest warship classification, too small to carry craft larger than an SKT-13 Shuttlecraft, used by the UNSC Navy and colonial system defense forces. Frigates and destroyers are larger combat warships equipped with heavier armaments, used for fleet escort and recon, and tend to make up the bulk of the UNSC fleets because they are cheaper to build, faster to replace, and can cover a greater volume of space than larger ships. Frigates tend to be faster and more evasive, while destroyers feature thicker armor and heavier armaments. Larger capital ships are build for dedicated ship-to-ship combat. Cruisers tend to form the cores of UNSC fleets, serving as fleet command and control ships in the absence of larger carriers. Carriers are large but lightly armed warships that transport and deploy large numbers of fighters and dropships in support of both space combat and planetary assaults. After the Human-Covenant War the UNSC operated at least one battleship class.
The Covenant operate a number of warship classes, but their classification systems are more esoteric, and the UNSC have struggled to correctly determine their roles. The Covenant designate their own ships according to primary, secondary and tertiary roles, using a three-letter designation system. The UNSC designate them according to their estimated roles analogous to their own ships. Covenant fleets tend to be built around powerful cruisers of various sizes designed to engage enemy fleets and support ground forces and bombard enemy positions from orbit, escorted by smaller but powerful frigates and destroyers. Covenant fleets tend to use carriers, assault carriers or supercarriers as flagships, though the largest ships are also the rarest. While the Covenant deployed its modern ships against the UNSC during the Human-Covenant War, it also kept a large number of pre-Covenant Sangheili-designed ships in service in rear-echelon duties escorting shipping, deterring and responding to piracy, and responding to local problems to free up modern ships for active duty. In the post-war era, these ships have assumed frontline roles among both Covenant and Swords of Sanghelios service as both sides have struggled to maintain and replace combat losses of newer, more powerful ships. They use a different designation system to either the Covenant or the UNSC, tending to be named for pre-twentieth century ships, such as the Blockade Runner and the Man O' War. While upgraded to modern technological standards, these ships are built for specific mission roles, like UNSC ships, and less capable in multirole service.
While naval combat is the purview of capital ships, smaller craft are used by the UNSC Navy, UNSC Air Force, and Covenant fleet in a number of roles. The most common human starfighter, the GA-TL1 Longsword, is able to perform a wide range of combat operations including escort, minelaying, spacefighter interdiction and direct action against even capital ships, using a range of variable armaments. The smaller F-41 Broadsword is similarly capable of performing a number of mission roles. The advanced YSS-1000 Sabre fighter saw use during the Fall of Reach and is still employed in more limited numbers by the Office of Naval Intelligence to protect classified sites. The spacefighter class pioneered the use of energy shielding on human spacecraft, which was later adopted by modernized Broadswords. Both use a combination of 30mm and 35mm autocannons (respectively) and ST/Medusa missile payloads to engage enemy forces. During boarding operations, UNSC forces use specialized Pelican dropship variants to cut through the outer hull of a ship and deploy forces within to secure it.
The Covenant's primary spacefighter is the Type-31 Seraph fighter, used in a similar role to the Longsword in escort, interdiction and direct action engagements by the less durable but more numerous Type-27 Banshee and heavily armed Phantom gunboats. Covenant troops use Type-44 and Type-52 Phantom dropships and other boarding craft to deliver boarding teams to secure hostile ships or space stations.
The conduct of space warfare varies significantly between the Forerunners' height and modern times due to the impact of the more advanced technologies employed in the former era in both strategic and tactical contexts. In addition, both the Covenant and UNSC fleets emphasize different strategies and tactics governed by technological capability.
Space engagements carried out by Forerunners and their technologically equivalent contemporaries—most prominently ancient humans—were dazzlingly complex yet controlled affairs, involving seamless coordination across large distances as well as weapon systems and defenses extending through higher space-time branes. These battles unfolded at speeds impossible for baseline individuals to follow and often involved copious numbers of often automated attack craft, with each maneuver adjusted to fit the current tactical situation according to constantly shifting predictive higher-dimensional calculations; biological commanders could effectively contribute to these engagements due to sophisticated neurocognitive enhancement and mind-machine integration, enabling them to simultaneously perceive numerous differing viewpoints. Individual Warriors would typically command up to a million weapon-ships during fleet engagements, while the numbers of attack ships such as harriers could easily be in the hundreds of thousands. In addition to physical weaponry, opposing ships also deployed weaponized AI systems and confinement fields against one another with the intent of eliminating the enemy vessel's capacity for resistance. Higher-level combat skins such as war sphinxes blurred the line between infantry, aerial attack craft and space fighters and were used to a great effect in battles waged over planets.
The Didact devised a well-known strategic doctrine known as "star-hopping" which involved the selective targeting of strategically significant worlds while ignoring less important targets. This strategy allowed the Forerunners to gradually dismantle the prehistoric human empire piecemeal during the human-Forerunner wars, eventually leaving only their capital Charum Hakkor as a significant military bastion. During fleet engagements, the Didact favored the fleet spiral formation which enabled a fleet to respond to threats from any direction. Late into their war with ancient humanity, the Forerunners took advantage of their superior understanding of slipstream space to catastrophically increase their human opponents' space-time debt, effectively cutting the Charum Hakkor system off from the rest of the ancient human empire. Over three years, the Didact fought the Lord of Admirals' forces across the Charum Hakkor system in a constant battle of attrition for superior orbital paths and optimal slipspace pathways.
During the Forerunner-Flood war, the Forerunner forces led by the Falchion at the 78th Thema used their numerous attack harriers' cloaking capability to catch a Flood fleet by surprise, utilizing gravity slings to propel asteroids at the arriving Flood ships rather than attack with traceable energy weapons, allowing them to attain victory. However, the conventional rules of space combat ceased to apply once the Flood began to use reactivated Precursor structures to systematically cripple and devastate Forerunner fleets. Additionally, the computing power of Flood Key Minds allowed the logic plague—the Flood's information equivalent—to eventually infest nearly any Forerunner ancilla, severely hampering their largely AI-driven fleet operations. Because of the Flood's rate of expansion, Forerunner fleets would often resort to triggering stellar collapses once an infestation had been detected in a system.
Space battles between the major factions in the modern era are fought almost exclusively within the context of normal space-time, although precision slipspace jumps and faster velocities within the slipstream offer increased tactical maneuvering options as well as considerable strategic benefits. The vessels involved are typically directed by individuals with baseline reflexes delivering tactical commands verbally, placing certain upper limits on the speeds at which ships and fleets can respond to threats and changing tactical situations; under the control of an AI, a warship becomes far more combat-effective due to the constructs' significantly faster reactions and information processing capabilities.
Naval engagements between the UNSC and the Covenant have typically been one-sided affairs. During the Human-Covenant War, the Covenant possessed an overwhelming technological advantage, with superior weaponry, defenses and slipspace navigation. In large-scale engagements, the UNSC has been forced to rely on overwhelming numerical superiority just to fight the Covenant to a standstill. In its first engagement with the Covenant at Harvest, the UNSC fielded forty warships and lost thirteen to destroy a single Covenant warship. By 2530, it took a fifteen UNSC ships to destroy three Covenant ships. By 2552, an advantage of three-to-one was the general rule to ensure a UNSC victory.
Human fleets have also been forced to rely on innovative use of strategy and tactics to counter Covenant naval doctrine, which has largely remained unchanged throughout the war, resulting in surprising UNSC victories. Admiral Preston Cole won the Battle of Psi Serpentis by using complex slipspace maneuvers, and unexpected Insurrectionist help to cover the retreat of the UNSC fleet and lure a Covenant fleet around the gas giant Viperidae, then launching a hundred Shiva nuclear missiles, triggering stellar fusion and briefly turning Viperidae into a brown dwarf, annihilating more than three hundred Covenant ships to seventy UNSC and 14 Insurrectionist ships and the presumed loss of UNSC Everest with Admiral Cole aboard her. During the Battle of Sigma Octanus IV, Captain Jacob Keyes' use of a complicated and risky maneuver allowed a single UNSC destroyer to defeat two Covenant frigates and a destroyer, forcing the unsupported DDS-class carrier to withdraw after deploying ground forces. In the second large-scale engagement, the UNSC massed its fire for a coordinated MAC salvo, using a repair station as cover against the Covenant's plasma torpedoes to buy time for a second, devastating salvo, reducing the Covenant fleet from twenty ships to eight, allowing the forty eight UNSC ships to engage the enemy in a clear advantage, a tactic repeated on a larger scale during the Fall of Reach. During the Battle of Onyx, Admiral Patterson's battlegroup used innovative tactics to destroy a disproportionate number of Covenant warships. After using intelligence gathered by the prowler UNSC Dusk to destroy a destroyer, the battlegroup encountered a much larger force attempting to ambush them. Faced with a plasma torpedo salvo, the fleet accelerated into it to forestall a second volley, allowing five ships to survive to escape through the Covenant fleet. A number of Covenant ships were destroyed by the self-destruction of the UNSC Iwo Jima, taking two warships with it and damaging another six. While the Covenant fleet was distracted fending off an attack by the native Onyx Sentinels, the Dusk laid a HORNET minefield. The battlegroup lured the Covenant fleet into the field, destroying all but two before Covenant reinforcements arrived, destroying all UNSC ships except for Dusk. In all, the UNSC battle group, consisting of one carrier, one Marathon-class cruiser, six destroyers and a prowler managed to destroy a total of twenty Covenant warships, a staggering number.
In general, the Covenant employ straightforward strategy and tactics, standing their ground, even to the death, and accepting no surrender. More complicated maneuvers are generally unnecessary given the Covenant's overwhelming edge in most engagements. This is not a hard rule, however. The withdrawal of the carrier from Sigma Octanus after deploying ground forces was remarked upon as unusual, a tactic repeated during the main invasion of Reach, and the Covenant used a number of innovative tactics during the Fall of Reach, managing to insert a cloaked CSO-class supercarrier past Reach's defenses to surreptitiously land ground forces and heavy corvette support in its search for Forerunner artifacts in advance of the main Covenant fleet. Then-Supreme Commander Thel 'Vadamee was considered by the Office of Naval Intelligence as the Covenant's best strategic asset, resulting in the loss of at least seven colonies and more than a billion casualties, and was marked for assassination before the end of the war concluded hostilities.
In the post-war galaxy, humanity's adoption of accurate slipspace drives and energy shields have considerably improved their capabilities against warships employed by Covenant remnant factions. Notably, the UNSC Infinity intervened to support Thel 'Vadam during the Blooding Years, effortlessly destroying a number of ships loyal to the Servants of the Abiding Truth. During the New Phoenix Incident, the UNSC fleet engaged the Forerunner warship Mantle's Approach and the Infinity used its MAC weapons to create a hole in the ship's hull large enough for the Master Chief to pilot a Broadsword fighter deep into it. During the Requiem Campaign, Infinity collided with an RCS-class armored cruiser, plowing through it with no hull damage and shields intact. It should be noted however that the Infinity is the UNSC's most advanced current starship, and uses Forerunner technology to power its systems, and is likely not representative of overall UNSC naval capabilities.
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