Covenant spacecraft design

The Covenant have access to a large number of technologies not available to the UNSC. The most obvious of these are energy shields and faster slipspace drives, but the Covenant enjoy numerous advantages that laymen observers easily overlook.

Sangheili origins
As the primary caste and co-founding species of the Covenant, most spacecraft naturally trace their design lineages back to the legacy established by Sangheili starfarers prior to the War of Beginnings. When the Sangheili first began their space travel pursuits in the 1820s BCE, spacecraft followed design techniques and styles that may be familiar to a 20th century human observer. This was due to the sheer issue of physics dictating the design of spacecraft; the need for rounded hulls for pressure containment and aerodynamic forms were all designed for safety and practicality. These spacecraft were built in a largely function-over-form attitude in this era, with the Joorian Reconquest seeing great advancements in the development of such vessels ultimately culminating in the development of the Blinker drive - a rudimentary form of slipspace travel that opened up the stars for Sangheili explorers.

As industrialisation and mastery of space grew, the Sangheili became able to place a greater importance on aesthetic in spacecraft design. While primarily seen in civilian and luxury spacecraft, some elements of curvilinear architecture began to make their way into spacecraft of the era. Notable design features, such as radiators, slowly began to take the form of extravagant "fins", often seen glowing a dull red against the darkness of space. Later advancements allowed for the employ of more advanced kinds of radiator such as liquid droplet cooling; employing magnetic fields to guide droplets of magnetic liquid through space to siphon off thermal energy into the vacuum. As the mastery of this technology grew, so did the fanciful applications of it - trajectories could be altered depending on cooling needs. Ships began to see their reliance on external fins and spines lessen as droplet cooling became the norm, with the aforementioned fin structures slowly growing smaller and less prevalent over time. As such, ships relying on droplet coolant were able to adjust their radiation to suit demand, and a ship engaged in heavy burns or combat might unfurl a large "sail" of arcing droplets to vent more heat. Droplet cooling also held another advantage over fins; these systems were less vulnerable to being destroyed by weapons fire, allowing ships employing them far more endurance in space warfare.

A common side effect of the magnetic systems employed in these era was the tendency of ships to capture interplanetary and interstellar hydrogen; over time this hydrogen would accumulate in the magnetic fields, heating up over time. When combined with the hot metallic droplets in the radiation system, the glowing gas and particles were able to form brilliant displays of colourful light, which was eventually adopted by the Sangheili as part of an aesthetic display.

Mastery of metallic droplet technology also saw early Sangheili spacecraft experimenting with electromagnetic weaponry; a common weapon in this era consisted of superheated metal droplets, streams or particles fired through space on paths controlled by magnetic fields.

By the time of the War of Beginnings, assembly forges, first introduced during the preceding centuries, represented the peak of the Sangheili's shipbuilding capability. The forges were a Sangheili innovation, the peak of the species' science at the time, as they sought to perfect their own unique methods of making in accordance with their faith and the one commandment most of the species subscribed to: thou shalt not tamper with holy relics. The emergence of the assembly forges proved to be a huge breakthrough in the construction of spacecraft, allowing ships to be built as collections of skeletal compartments than their exteriors "filled out" by the forges. Initially, the forges were not large enough to construct large capital ships, and were instead used to construct individual ship components. Although the forges were initially pioneered by one of the major Sangheili polities active at the time, active trade and industrial espionage ensured that the major states that would come into conflict with the San'Shyuum all had some form of assembly forge technology. Assembly forges were among the most prominent native Sangheili innovations maintained into the Covenant and never replaced by Forerunner-sourced technologies; not only because of the scarcity of intact Forerunner manufacturing centers, but also due to the sheer versatility and efficiency of the forges.

Covenant Antiquity
By the time of first contact with the San'Shyuum at Ulgethon in 876 BCE, the conventions of Sangheili spacecraft design had become well-established. However, the resulting conflict with the San'Shyuum and their dreadnought Anodyne Spirit saw the Sangheili spacecraft hopelessly outmatched in space, despite fierce resistance. Spacecraft of this era were slowly beginning to adapt to the usage of paragravity in their design, though many ships retained internal layouts indicative of a reliance on thrust or centrifugal force to provide gravity.

As the Covenant alliance began to solidify itself, technology exchanges between the Sangheili and San'Shyuum saw the spacecraft employed by the empire begin to take the forms recognisable and iconic in the empire's later years. What had once been gracefully arcing magnetic fields became the curvilinear forms of the ships' hulls, and the radiator fins evolved into sweeping wings and sensor vanes.

Some early schools of Covenant shipbuilding were inspired by the Forerunner keyship, both the sacred vessel's stacked-deck layout (which was shared by prominent Sangheili traditions) and the trilateral symmetry of the Forerunner vessel. As antigravity technology became established and even large capital ships took on roles as planetary assault vessels, operating in an atmosphere became easier and was prioritized in doctrine for most ministerial ships. This meant that "horizontal", thrust-parallel deck layouts became increasingly common, even as some early planetary assault ships were structured more akin to the Forerunner keyship.

Over the course of Covenant history, the advancement of ship design followed a broadly similar pattern as other Covenant technologies. As the hegemony's technological doctrines became more and more restrictive over time and power was centralized under the Prophets of High Charity, the independent development of spacegoing technologies slowed. As the Covenant uncovered and reverse-engineered Forerunner technology caches, starship design would often advance by great leaps over the span of an Age, to be followed by centuries of stagnation or merely incremental progression. While older ships still became outdated over time, the Covenant still kept ships in service for inordinately long periods of time by human standards. Depending on the technological schema of the time, ships over a thousand years old may still be found in service. While outdated vessels were phased out of ministry use, they found new lives in the service of regional polities and lesser lords, eventually being relegated to Vestige status.

Structure and construction
Covenant spacecraft range in size from singleships to colossal worldships dozens, sometimes hundreds of kilometers in length. While Covenant ships are larger than their UNSC counterparts, ships expected to partake in combat usually peak at around seven kilometers; beyond this, a ship is considered less of a warship and more of a mobile station or transport barge. This is due to many factors, including maneuverability, maintenance considerations, crew size, etc.

Power and propulsion
The Covenant have a variety of propulsion options for both sublight and superluminal travel.

Power generation
Most Covenant ships are powered by pinch fusion reactors, which use fine-tuned electromagnetic fields to induce fusion. The most common reactor designs use spin-polarized deuterium-tritium or deuterium-deuterium fuels, with gravitic fields used to moderate the resulting neutron flux, allowing them to achieve higher efficiencies than conventional pinch fusion would allow. The plasma generated as a byproduct of the fusion process can be fed into a ship's weapons network and fired as plasma torpedoes. Despite the rather exotic gravitic component of the reactors, UNSC engineers have noted that Covenant pinch fusion reactors are surprisingly primitive and ineffective for their power needs; indeed, they are one of the several Covenant technologies derived from a pre-Covenant Sangheili lineage rather than Forerunner sources. Because the power output of individual pinch fusion reactors is limited, large ships and facilities use clusters of multiple reactors arranged in parallel. Large worldships may house as many as several hundred reactors in one unit.

Although exceedingly rare, some Covenant ships and facilities have access to Forerunner power cores, which use exotic means such as matter-antimatter annihilation or vacuum energy siphoning to provide unprecedented amounts of power.

Repulsor engines
Repulsor engines are a category of maneuvering drives found on most Covenant vessels and craft. Repulsor drives energize small quantities of exotic matter to conjure virtual neutrons and protons from the quantum vacuum, which are then expelled as a relativistic plasma flow. These virtual particles blink out of existence fractions of a second after being expelled from the drive, though large repulsor drives in particular create hazardous quantum fluctuations in their wake due to their interactions with the local quantum vacuum.

The quantities of exotic matter required as a catalyst are minute compared to traditional propellants, and repulsor engines have no need for conventional reaction mass at all, being limited mostly by the power generation capabilities of the craft they are mounted on. This makes repulsor engines highly versatile and efficient. However, the manufacture of propellant for repulsor engines is a complicated and specialized process, which allowed High Charity to effectively control the distribution of such drives. Like most Covenant technologies, repulsor engines are an imperfect imitation of a Forerunner equivalent.

Antimatter drives
Antimatter drives are a form of high-efficiency, high-impulse propulsion used on some Covenant spacecraft.

Suspension drives
Suspension drives or suspensors are contragravitic devices that are used to counteract the effects of gravity on a vessel, allowing them to effortlessly operate within a gravity well. However, they cannot generate gravity gradients, and as such have little use outside a gravity well.

Plasma thrusters
Plasma thrusters or plasma engines are a far older lineage of drives, dating back to pre-Covenant times. Fundamentally similar to magnetoplasmadynamic thrusters, they use electromagnetic fields to accelerate an ionized propellant. While far less powerful and efficient than repulsor engines, their propellants are also far easier to come by, with many models able to use water or noble gases such as argon and xenon. This makes plasma thrusters a common choice for non-ministerial craft as well as various independent fringe elements.

Fusion thrusters
Fusion thrusters are a category of direct fusion propulsion drives. Fundamentally based on the same basic principles as human fusion drives, several varieties of fusion drives served as the primary form of propulsion on most War of Beginnings-era Sangheili ships. By the Covenant's later ages, few to no ministry vessels use fusion thrusters; they are limited to secondary polities, being common among the Kig-Yar in particular.

Sensors
The Covenant have access to more sophisticated sensor technology than the UNSC, although the hegemony's restrictions on artificial intelligence and machine learning limit these systems from being used to their full potential.

Most Covenant warships are equipped by sensor systems known to the UNSC as hyperscanners. Rather than a single type of sensor, these comprise an array of precise passive and active sensing equipment which collectively feed the ship with enormous volumes of data. Due to the Covenant's strictures on advanced computing, however, most of this data is effectively unfiltered and there are no automated pattern-recognition algorithms for detecting enemy vessels, for example. The data has to be manually sifted through by sensor operators, and it takes considerable skill (and a fair degree of intuition) to filter out the relevant information in any given situation. This is likely the result of much of the hyperscanner array being reverse-engineered from a Forerunner equivalent, which utilized sophisticated AI to filter the data.

One of the sensors included in the hyperscanner array is a type of highly sensitive and reliable radiation detector. While they have had such sensors for a long time, the Human-Covenant War saw them harnessed more widely as the Covenant caught on to the UNSC's use of nuclear weapons, including attempts to carry nukes aboard prowlers or launch them from slipspace. This imposed a hard limit on prowler capabilities, and the UNSC only managed to develop consistently effective means of masking radiation in the later years of the 26th century. Prowlers and other stealth vessels were consequently forced to circumvent this by relying on conventional explosives (such as octanitrocubane charges) and magnetic accelerator weaponry even as their stealth systems improved.

Should the opportunity arise or be deemed tactically prudent, it is also common practice for fleets to deploy observation buoys across a system to supplement a vessel's onboard sensor suite. Many models of these buoys are equipped with superluminal communications capabilities, allowing them to relay sensory data to the ship in real-time across many light-hours. Covenant-held systems, particularly those of their military and industrial hub worlds, are saturated with such sensors and constantly monitored. Prior to the Human-Covenant War, few in the Covenant expected an enemy to infiltrate one of their major systems. This changed with Operation: SILENT STORM and the destruction of Zhoist's orbital ring. This incident shook the Covenant out of their complacency, and every strategically important system (particularly in the spinward side of the Holy Ecumene) had its sensor capabilities subsequently augmented, with legions of operators per system trained solely to watch for human infiltration attempts day and night.

The most powerful sensor in Covenant use is the Forerunner-derived Luminary, a highly advanced and versatile superluminal sensor capable of scanning large volumes of space in real-time. Though little escapes a Luminary's notice, they cannot be used indiscriminately due to several limitations. By the Human-Covenant War, most Covenant ministerial vessels were equipped with Luminaries.

Outside ministerial vessels, sensor systems are often more eclectic and conventional.

Communications
Covenant warships rely near-excluisvely on wavespace-based superluminal communications, with conventional, lightspeed transmissions being reserved for short-range devices and backup options.

Gravitics and paragravity
It goes without saying that the Covenant have a much finer understanding of gravity, and their control of it outstrips what UNSC scientists have ever considered possible. Far beyond simulating gravity in space habitats and starships, the Covenant can move massive objects with gravity lifts and lock them in place with tow fields. Otherwise impossible structures can be sustained with active gravitic support, and ships can endure otherwise fatal maneuvers with the aid of deft inertial control. Paragravity technology may be used for the most mundane of applications, but the Covenant's byzantine logistics systems would grind to a halt without them.

The Covenant possess gravitic weapons such as Brute hammers and gravity cannons, but the largest of these are mounted on small ground vehicles. Power and control requirements scale exponentially with size, and the Covenant simply do not possess the technology to build starship grade weapons. Gravitic starship weapons have been a holy grail of warship designers for thousands of years. Such weapons bypass shield and armor, and the Covenant have encountered Forerunner defense drones armed with such weapons. Usually fatally.

Holograms
Although the Covenant do make use of holoprojections for their infantry forces, they are comparatively rare on naval vessels. This is largely down to the sheer difficulty to replicate something as complex as a starship - not only does it need to fool the sophisticated sensor suites available even to lowly freighters, but it also needs to behave as expected and maintain its image over dozens, if not hundreds of kilometers. It is also because of religious limitations, as the only way to achieve this is with the use of highly-advanced AI software.

Still, the Covenant is not above its use. By its end, some shipmasters could requisition disposable holographic missiles for select missions, though the overbearing bureaucracy made them very, very rare sights. More commonly, the technology was found aboard specialized 'ghost ships', although even these were uncommon.

The sole exception is in the field of low-frequency holograms, which by the Consolidation Period are carried on all modern Ministry warships. Near-imperceptible to the vision of most species, these are instead used to generate false images on sensor screens. None of these are powerful enough to generate complete, independent copies of the mothership, with their range restricted to within a hundred meters of their emitters. Instead, they are used for deception and jamming purposes, to obscure hull damage and to subtly alter the ship's profile and shape to convey false course changes and throw off aim. Though useful at extended fighting ranges, at close distances it is easy to tell the difference between the projection and the actual ship.

Weaponry
Like the hegemony's ground forces, Covenant starships mainly rely on directed-energy weapons. These include pulse lasers for point defense, both guided and unguided "bolide-type" plasma weapons (plasma cannons and plasma torpedoes) as well as "beam-type" plasma projectors (excavation beams, plasma beams and plasma lances). The most common projectile-based weapons are various types of missiles, most of them also carrying a plasma payload.

Plasma torpedoes
Plasma torpedoes, known to the Covenant as seeker spears or energy spears, are a category of guided, bolide-type plasma weapons. Rather than being conventional projectiles as their UNSC moniker might suggest, plasma torpedoes are composed entirely of superheated plasma held in a globular electromagnetic envelope projected from the ship. The individual torpedoes are fast, highly maneuverable, and difficult to dodge. As humanity quickly found out, they are also impossible to counter with kinetic point defense. The only reliable defense is to absorb the shot with a physical or energy shield or somehow remotely disrupt the EM envelope; early UNSC options included forms of chaff and superheated gas, while later developments focus on targeted magnetic gradients or point-defense missile screens with plasma-based payloads. Plasma for the torpedoes is drawn directly from the ship's reactor, and the weapons also have a highly variable yield that can be fine-tuned by the operator. Both this and the steering of the torpedoes is usually manually controlled, and skilled gunnery operators turn the fine-tuning and steering of energy spears into an art. Indeed, spear-steering is one of the most treasured martial skills within the Covenant fleet. At the higher settings, plasma torpedoes are devastatingly powerful weapons, easily gutting UNSC vessels with single hits.

Like their advantages, the downsides of the plasma torpedoes also come from their unconventional nature. The operational range of the magnetic field emitters used to control them limits the weapons' effective range. A torpedo loses effectiveness and cohesion the further it is from the ship, along with becoming increasingly vulnerable to magnetic interference, which makes them most effective at short ranges. Though some patterns of energy spear sacrifice power for range, this can only go so far, lending torpedoes their niche as short to medium-range heavy-hitters. Another downside is the power drain their use imparts on the ship's overall energy budget, especially when used at higher settings, forcing shipmasters to balance between weapon effectiveness, shielding, and maneuvering. As they are held together by magnetic fields, plasma torpedoes are also sensitive to magnetic fields, ambient ionization and atmospheric turbulence, the magnetic fields used to hold them together unraveling upon encountering such disturbances on all but the shortest distances. Anti-plasma torpedo point defenses seek to take advantage of this phenomenon, while in Covenant doctrine it is common to either attempt to move out of the way, absorb the bolt with the ship's shields, or even counter the plasma spear with another; doing so successfully is rare, but possible.

Due to the immense energy buildup involved in torpedo launches, use of the weapons puts a great deal of strain on the launcher, causing rapid wear. To avoid this, the launchers use expendable coil sheaths, principally comparable to a sabot or the replaceable rails of a railgun, to both protect the fixed components of the expensive launcher and to further focus the torpedo's projecting field. Depending on the energy level of torpedo launches, the sheaths must be replaced after a few shots or even each shot. These sheaths are sometimes known as plasma torpedo "tubes" by the UNSC as an extension of the maritime analogy, even though the comparison is technically inaccurate. Other names include "torpedo cores", though this is likewise inexact since the sheath is not part of the torpedo after it launches. Still, they put a limit on how many torpedoes a ship is able to launch without restocking, approximating the role of ammunition in ballistic weapons.

Technologically speaking, energy spears are relatively similar to linear-fire plasma beams. The nature of bolide-type plasma weapons such as the energy spear (as well as ground weapons, e.g. plasma rifles, plasma pistols or plasma mortars) has perplexed human researchers, mainly because it appears very counterintuitive to all prior forms of human research into directed-energy weaponry. As demonstrated by Cortana's example on the Ascendant Justice, it would seem more straightforward to simply make a weapon that strikes its target instantly, rather than going through the added effort of generating and maintaining self-sustained bolts of plasma in individual magnetic envelopes. Although much more technologically convoluted, this has some benefits: plasma torpedoes can curve around obstacles, for example, though in the reality of space warfare, this is rare. Indeed, the Covenant do have access to such technology in the form of their beam-type plasma weapons, though they do appear to be a more recent discovery. Some scientists have speculated that bolide-type plasma weapons may have originated as an early synthesis of two distinct Forerunner technologies: ranged precision magnetic field projectors and some form of industrial plasma emitter. Others suggest that they were indeed sourced from a type of Forerunner weapon, but perhaps one more versatile than the Covenant's largely function-fixed weapon systems.

It is apparent that bolide-type and beam-type weapons, despite their similarities, are part of two entirely distinct technological lineages within the Covenant. It has been suggested that, due to their restrictions on AI and high-level computing, the Covenant simply never made the connection due to fixed patterns of thinking in regards to the two categories, or were unable to; on the Ascendant Justice, it took the immense processing power and pattern-recognition ability of a specialized smart AI to do so. Post-war experiments with sympathetic Concord shipmasters have confirmed this; without a military-grade "smart" AI, plasma spears cannot be reconfigured into scalpel-type beams without extensive hardware modification. Some lines of research have suggested that the process involved might be automated by a purpose-built "dumb" AI, but Concord commanders' reluctance to allow AI on their ships has slowed progress.

Under the Covenant, plasma torpedoes were entrusted technology, with High Charity's formal institutions reserving the rights to their manufacture and maintenance. In practice, however, over the last millennium several wealthy guilds, kaidons and regional lords have had access to the manufacture and maintenance of many types of energy spears, though they remain uncommon outside the ministerial armed forces.

The UNSC term "plasma torpedo" arose in the first years of the Human-Covenant War. The weapons the Covenant used were plasma-based, difficult to avoid, and were used to gut ships, so Navy crews called them torpedoes. For some time, it was not even clear which of the torpedoes had a physical core and which ones did not. Over time and more data from engagements, distinctions arose as ONI identified more types of ship-to-ship weapon, but "plasma torpedo" persisted for some time as a general name for guided Covenant starship munitions. Formally, "plasma torpedo" came to refer to magnetically contained vapor-core energy munitions, while "plasma missiles" were defined as solid-core guided projectiles that could be physically countered. Other UNSC categories, like "energy projector", are similarly ambiguous. Formally, ONI classifies any non-projectile plasma weapon (from plasma torpedoes to lances) as a "directed energy projector", though early on the term mostly referred to direct-fire weapons and plasma lances in particular. Part of these ambiguities is simply the UNSC's difficulty in categorizing Covenant weapon systems, which can vary quite drastically between different ministries and based on the age of the weapon; as the Covenant frequently recycle technological components, some weapons or their parts can be thousands of years old.

ONI classifies plasma spear-type weapons as "Type-XX Directed Energy Projector/Nonlinear".

Missiles
The Covenant uses a variety of guided solid-core starship weapons, which are generalized as "missiles". The most common subtype of these are missiles carrying plasma-based payloads. Other types of payload include antimatter, fuel rod, subanite, and even nuclear explosives. All but the most advanced types of missiles are sanctioned technology and manufactured by armories across the Holy Ecumene.

Plasma missiles are the Covenant fleet's all-rounder weapons. They can strike at medium to long ranges, and many are built to have some resistance to laser point defense through the use of iridescent refractive coatings. However, as the Covenant quickly found out in the war with humanity, they are vulnerable to kinetic point defense which UNSC ships largely rely on. As a result, they experienced a steady decline in usage throughout the human campaign, with Covenant fleets favoring energy spears against human ships, while the missiles remained a staple weapon in the Covenant's internal conflicts. Unlike plasma spears, firing missiles has virtually no energy cost for the ship, but as a downside, they also take up more space and add mass on the ship. Most mainline patterns of plasma missile are self-guided, and therefore less precise than plasma spears due to both the missiles' limited propellant reserves and the Covenant's limitations on autonomous intelligence. Some missiles are known to have been built with embedded wavespace links for guidance, but these are rare and expensive.

Ship types and classifications
The Covenant use several systems to classify their spacecraft. Ship production models are identified by their design pattern, specific to select assembly forges. Ships of broadly similar tonnage and role can be grouped together into classes, although classes can be quite loose when it comes to Covenant ships. Finally, the Covenant ministries use a system of orders to designate ships based on their operational niches.

The UNSC uses a letter-based designation system to identify Covenant ships, though it has become apparent that many of these categories are partly incorrect and do not always correspond to the Covenant's categorization systems. Ship classes were identified by human categories (e.g. frigate, cruiser, carrier, etc.) according to their apparent role, though these categories were not always shared by the Covenant.