Celestia-class assault ship

Celestia-class Assault Ship "Not exactly the newest ship in the Fleet, but four centuries of tack-on upgrades later and she's as formidable as ever."

- Captain Tyler Finch, commander of the HMS Celestia

The Celestia-class Assault Ship, also known as the Celestia-class Cruiser, was a warship class in service with The Royal Allegiance Navy, and later the UCG Navy during the Swarm War.

History
Ancient even by the Human-Covenant War, the Celestia-class Cruiser was introduced in 2429. This was less than a decade after the Reformation War when the Allegiance Navy was extremely weak, and in need of a vessel to reassert its power. When it was introduced, the Celestia-class was the most well armed, fastest and best protected ship of her class. She was a cruiser; designed to be an all-round powerful vessel able to defeat even the most powerful enemies. By the time of the Human-Covenant War, however, its better days were over; despite this, the Allegiance's involvement in the war saved the class from decommissioning at the last minute. It was able to take on and defeat three CCS-class Battlecruisers with its fighter support, though newer Allegiance vessels could achieve double that. In 2593 the class was relegated to armed freighters, transporting goods to UNSC, Sangheili and Allegiance worlds with little fear of attack.

The class was still serving in this role a hundred years later, being more than properly armed for self defence and with more capacity than most other armed freighters. The class, now designated the Celestia-class Freighter, was the most numerous non-combatant vessel type in the navy. It was also the most easily armed and the most well armoured, having formerly been a cruiser. As the Swarm War progressed and the Allegiance found themselves ever pressed to find ships to send into battle, the Celestia was the most obvious choice, and in 2784 the class was extensively updated, modernised, refitted and brought up to 28th century standards. Renamed the Celestia-class Assault Ship, the vessel once again could be seen as part of Allegiance battlegroups. It was finally decommissioned in 2880, after the War, and more than 400 years after their introduction. It is this, final iteration of the Celestia on which this information is based.

Role
Officially, the Celestia's main role was that of ground support, providing fighters and heavy fire support to ground units against Swarm forces. However, the nature of the war forced the vessels into virtually every role, from ship combat to escorting more modern vessels. Most newer Allegiance vessels were specialised to one particular role with secondary abilities in other ones. This allowed for greater combined force actions with multiple warships. However, the Celestia was designed in a time where warships were largely independent from each other, and as a result, the class was essentially a hybrid between a cruiser and a carrier; officially named Assault Vessels but widely known throughout the fleet as Battlestars. These vessels were, relatively speaking, more independent than their modern counterparts, which lent them the advantage in combat, and led to them being used on their own. Their dual cruiser/carrier nature gave them the advantage when facing both, and essentially negated the Swarm's reliance on fighters by meeting them with both more fighters and more firepower, all in a single warship.

More often than not Celestias were found in lone groups of two, operating far from reinforcements and additional naval forces, where they could use their multirole nature most efficiently to deal damage to the enemy.

External Layout
The Celestia-class's design was dissimilar to virtually every other ship class in the fleet, sharing design traits with ancient vessels that served in the Reformation War of 2416-20. The front of the vessel was made up of a sloped frontal section, split into the larger upper and smaller lower keel and vaguely resembling an arrowhead. Between the two were the four main guns, embedded deep inside the ship away from harm. The midsection of the ship was a broad, flat section where the ship's flight pods were mounted, with large support pylons connecting them to the rest of the ship. These pods housed large flight decks, which substantially reduced fighter scramble time. The stern of the craft mounted the large sublight engines, four in outboard pods and two in the rear of the superstructure.

CIC
The CIC, or Combat Information Centre, also known as the Command Centre, was the nerve centre of the ship, responsible for commanding and controlling the vessel. It was located very close to the core of the vessel, in the most protected area from enemy fire. It served as both the CIC and the Bridge as the vessel was both steered and combat action commands issued from here.

The Celestia-class's CIC was a fairly sized room located deep in the interior of the midship section of the vessel. From the bridge, the ship's tactical and navigational operations were monitored and directed. The CIC was a large, two-level complex with four automatic bulkhead exits, which were closed during action stations alerts.

The CIC consisted of many stations arranged in a concentric layout around a central command area. Here there was a single primary battle holoprojector, which showed in real time events unfolding on the battlefield, as well as detailed information on the vessels and objects shown (damage taken, crew, complement, standing orders etc). Alongside this were three secondary and numerous tertiary holo-displays, in addition to several Holographic Displays. Several large, flat holographic displays about 2 metres long and 1.5m high were projected from the top of the peripheral stations. This gave the officers stationed there an additional large display, and also allowed the commander to easily see the station's information from his post.

Command and Control
The CIC was divided into several stations, the most imperative being Command and Control. The Command and Control station was the primary station within CIC, used by the Commanding and Executive Officers aboard the vessel. The centre comprised a large communications and a roughly hexagonal "information management" holo-table, with a retractable information display tower bearing a number of MPHD screens suspended above it. There were no chairs; the command staff were always standing.

Here, the ship's commander and Executive officer were on station, observing and plotting battle tactics, viewing holo-charts, and giving commands to others in CIC. Above the Command and Control Station was a cluster of holographic monitors displaying additional secondary information. This console descended from a cylindrical ceiling recess when required. From the Command and Control Station, the commander had a 360 degree view of the CIC. The console contained multiple sensor displays but also included other navigation and tactical information available to the commander and others at a glance. The displays were capable of showing a wide range on information including countdowns, sensor readings relayed from the sensor console, and vessel management information, such as the vessel's spatial orientation (pitch, yaw & roll).

Communications
Adjacent to the Command and Control Centre on the port side of CIC was the Communications Center. Here, all communications to and from fighters and other ships were monitored, directed or relayed. In coordination with the Tactical Station, the Communications officer could also verify transponders that register as friendly, and alert the Tactical Officer or commander of any signals without transponders or recognised enemy transponders. The Communications Officer had a link to the mainframe computer, where a library of Allegiance recognition information resided.

Damage Control
Situated in the far port side of CIC was the Damage Control station. Usually unmanned, it contained the Damage Control computers, which connected to thousands of sensors throughout the exterior and interior of the ship. A large display against the wall of the station showed damage through a holographic display that showed the extent and location of damage on the ship, and could display multiple views of both the Celestia's interior and exterior. A commander could order a Damage Control officer to perform many actions to repair or mitigate the effects of an enemy attack through the controls here, including the venting of compartments, coordination of damage control teams and the like. The station worked in tandem with numerous other damage control stations situated around the ship, the main one being the Aft Damage Control room, which contained similar controls to aid in repairs, control of fires and such in the event that the CIC's damage control was knocked offline or CIC staff were incapacitated.

Navigation
The navigation station, not essential enough to be constantly manned, was a station that handled both long and short range navigational data. However, most of its functions could be operated by other stations.

Helm
The Celestia-class moved through space relatively unneeding of visual coordinate telemetry. Though numerous visual sensor devices were available to the helmsmen and could be shown on his station, there were no windows, no viewscreens to see into space for helm control. Navigation was managed by spatial coordinates based on sensor and other information. The helm crew members drive the vessel through a series of intuitive controls and based on commands from the Executive officer or commanding officer. The helmsman often linked neurally to the ship's control interface, allowing him or her to flawlessly direct the ship's actions.

FTL
From this station, FTL courses were executed. Not routinely manned, the Tactical station plotted the course and transmitted the coordinates to other vessels, while the actual execution was operated from the FTL station by the Tac Officer. The station contained a large amount of sensory information pertaining to long range FTL travel not displayed by the Tac station. The station shared a direct link to both the Navigation and Tactical Stations. Like all bridge positions the station was assisted by an AI.

Tactical
The Officer of the Watch, or Tactical Officer, was arguably the busiest officer in the Celestia-class's CIC. Assisted by an AI, he or she was tasked with the monitoring of sensors and coordinating various command and control functionality. The Tactical Officer was required to relay changes in status and keep the commander updated continuously during the fluid events of battle, in which they were assisted considerably by advanced computer systems and the several advanced AI on the bridge during a combat situation. The Tactical officer was typically the first to know that an attack was imminent and either he or an AI would address the vessel by the public address system to go to battle stations through Condition One or Two alerts. From here the AI was typically issuing general crew orders to the rest of the vessel, from where it had quickest access to information. Orders commonly issued by the AI were to individual crew members to report to their posts, starfighters to launch, and other ship-board actions. The AI could know where every crew member was simultaneously, removing the need for the Tac Officer to divert his attention and use his console to locate a crew member.

While the Helm officers controlled the ship's movement, it was the Tactical officer that plotted FTL courses. The Tactical officer of the ship provided destination coordinates to the vessel's helm, through a link between their two stations. They relied heavily on their AI to provide other accompanying vessels of combat information and FTL coordinates, where the multiple ship AIs would share information and adjust various conditions on their vessels accordingly. This was not the only, but one of the most important, links between allied vessels.

Nearby the Tactical Station was a tactical board and table where the commander could meet with several officers and crew at once for advanced battle or strategy conferences. The Tactical Station was frequently manned by other specialists and officers that assist the Watch Officer in addition to its AI.

Weapons Control
The Weapons control station was a position located to the far starboard of the bridge, and manned by two or three officers as well as a remotely linked AI. Together they were responsible for the vessel's offensive and defensive weaponry, the AI being a vital asset to target acquisition, gun/target designation and actual targeting and firing. One single AI could operate the entire vessel's weaponry, ensuring a cohesive and uniform firing pattern and meaning that nothing could slip through due to multiple targeting systems, or multiple gunner crew members. The officers at the weapon station were nonetheless essential in power regulation, shielding control and combat sensor monitoring, in addition to the weapon control crews assisting each weapon in battle. In the event of the station being destroyed, the remote AI could continue to fire the ship's weapons unhindered, with the assistance of the gunners at each weapon and the secondary fire control stations throughout the ship, such as the Auxiliary Fire Control station located in engineering.

Engineering and Environment
The engineering and Environment station was similar in function to main engineering, and in theory acted as engineering's representative position on the bridge. However in practice, it was often unmanned, usually where the senior technical officer on board would be stationed when he was in the CIC. Closely linked to Damage control, the two stations shared information, relevant to each other's function, as well as information sharing with engineering and the tactical station. However, unlike Damage control the Engineering/Environment station was not solely designed for use in combat; routine things such as atmospheric and environmental regulation, and other non-combat aspects of the ship could be controlled from here, though obviously some functions such as the sealing off of breached or compromised sections or the venting of atmosphere, and other such actions, were more closely related to combat situations.

Power Core
The vessel's power core was located deep within the Celestia's midsection. It was a large, semi-spherical chamber with the extractor core in the centre, from which the power was drawn. The core was linked almost directly to both the four main guns and the shield generators, being the most energy intensive systems on board.

Engineering
Engineering was located towards the rear of the ship, situated between the rear thrusters and the power core. It handled the maintenance, hardware and power aspects of the ship, arguably the most important location after the CIC, and was as a result just as heavily guarded. From here, crew and AI could more closely monitor the ship's systems that was possible on the bridge, and could in conjunction with the command crew execute actions to improve the ship's battle performance or ensure its survival. The Auxiliary Fire Control station was located in engineering, allowing the ship's weapons to be operated from this location. Indeed, the entire ship could be controlled from engineering if need be, though at the cost of operational efficiency. The Aft Damage Control room was also located in engineering.

Cargo and Complement
The ship's substantial fighter complement was stored in the ship's midsection, where they could be quickly deployed to the flight decks. The troop accommodation and vehicle storage was nearby, while the main cargo hold was located towards the ship's rear, and crew quarters in the ship's arrowhead front. The Celestia-class could hold over 242,000 metres squared of cargo, or up to 11,000 metric tons, their large capacity a strong reason they were used as armed freighters. In non-war time, their flight decks could be sealed up and repurposed as storage areas to more than double the ship's cargo capacity. The ship also stored large quantities of ammunition and weapons, both vehicle weapons, ship weapons and small arms and their ammunition. This allowed it to go for long periods without resupply, and also to reinforce ground troops and mount its own ground attacks with well-equipped troops.

Main Armament
The Celestia-class Assault Ship had an expansive armament that aimed to strike a balance between heavy antiship weapons and close-in weapons systems and point/area defence. Mounted on the prow were four Strategic Instruments DDP-278 Linear Particle Cannons, powerful and long range anti-armour energy weapons. The cannons each had an individual output of 50,000,000 Terajoules, 23,100 times the power of standard MAC rounds and enough to destroy many ships with just a salvo or two. As for the rate of fire, power was not the issue, but rather cooling. The weapons, unlike MACs, were prone to overheating. A single cannon could fire seven times before needing to pause to cool, but it could pause at any time in between. After a full firing sequence, the cannon would remain inoperable for three minutes at least before the barrel was cool enough to allow another firing sequence. The group of four cannons were arranged in 'fire groups' of two groups of two, each cannon firing alternately. In this way, a fire group could fire 14 shots before needing to pause. The three groups could together fire 28 shots before needing to pause, although they could extend this by leaving slightly longer periods of time between each shot. They had a range of around 360,000,000km, or approximately 20 light minutes. The weapon's faster-than-light nature meant that they had no chance of missing their target, even over astronomical ranges.

Secondary Armaments
On the dorsal side of the ship, as well as along its flanks, were a total of twelve MG9 Heavy Particle Cannon turrets, designed to blast through ship battleplate in broadside and long range. They fired in a fashion much like a semi-automatic weapon, one shot, then a period of 4 seconds to cool. The cannons were far less powerful than the main guns, though made up for this with their numbers. They had a power output of around 1,250,000 terajoules per blast, which was 40 times smaller than the main cannons. Their primary purpose was as heavy turreted weapons able to engage ships at both long and short range, especially those out of the main cannon's field of fire. The turrets were the primary engagement weapons after the internally-mounted stationary forward weaponry, and had two tracking modes. The first, precise, long-range tracking mode, the turrets could hit a target five meters wide at a range of four light minutes (107,925,285 kilometres). During close-range combat and fleet engagements, the turrets could rotate fully in under six seconds with their fast-tracking mode, able to hit the majority of slow and fast-moving vessels.

In addition, the ship's prow featured four heavy missile tubes, firing a wide range of anti armour missiles, with the ability to launch tactical nuclear missiles, often DECIMATOR ACSMs or VINDICATOR ACSMs. This powerful but variable armament gave the Celestia-class a unique and powerful weapon with short, medium and mid-long ranges.

The Celestia-class' frontal armament was supported by 6 M119 Heavy Naval Cannons. These heavy 900mm cannons, although a widely outdated armament, contributed to the class' heavy frontal armament, and were especially useful for engaging armour once the Particle Cannons had defeated any shielding. They were a relatively short range weapon, still used alongside the Particle Cannons for their variability. The cannons could be loaded with several weapon types (from RAPID, HEPAB, APFSTDS, HPSDAP, HPHE, HEPA and HVS/AP-HE), while the variability of Particle Cannons was restricted to the power of the blast, which could be selected from anything up to 100%. As a result, the cannons could quickly be changed from anti armour rounds to high fragmentation proximity shells almost instantly, in order to suit the threat faced, whereas the prow Particle Cannons were nowhere near as adaptable. The cannons used Electrothermal Acceleration to propel the shells, increasing their range substantially and giving them a muzzle velocity of 34,272 kph, similar to some railguns, and aiding in range, accuracy and penetration substantially.

Even still, there were still signs that the weapons, which had clearly seen more prominent days, were on the way out. The Celestia-class was initially fitted with six additional prow 900mm cannons. However, later models, from around 2730 onwards, replaced these with six modified MG9 Heavy Particle Cannons, in non-movable mounts, with their range extended by 30% to allow adequate frontal usage. Earlier ship classes, such as the Celestia pre-refit, had featured these 900mm cannons in large turrets as their primary turreted antiship armament, however these were largely phased out for the MG9 in the mid-2600s.

Bridging the gap between the larger MG9 turrets and the smaller M252 Point Defence turrets were 45 MD12 Particle Cannon turrets. These weapons were designed to complement the larger and smaller cannons, by supporting them in combat. They could act equally as point defence guns or as powerful anti armour weapons. They were roughly a third as powerful as the MG9 Cannon, though far more numerous and more effective at taking down smaller warships. They had a power of around 415,000 terajoules, and a range of about 50 million kilometres.

Providing a variable but powerful armament were 30 M125 Missile Launchers. The weapons were used as a versatile, powerful weapon able to engage multiple enemy types. Of the Celestia's arsenal, these missile launchers were probably the most responsive and variable, able to be changed between high fragmentation antifighter missiles to long range antimatter missiles in a matter of seconds, in accordance with the ever-changing battlefield. They were utilised in two main roles; point defence, using precision or area-damaging missiles to defeat incoming fighters at short and short-medium ranges, and anti-armour, for engaging all smaller warships and many of the larger ones too. In the latter role, the turrets often employed the DECIMATOR Anti Capital Ship Missile, which could easily overpower a cruiser or carrier with thirty to forty hits.

The weapon consisted of an armoured box-like multi tube missile launcher mounted on a fast-tracking turret. Powerful but compact sensors specialised for picking out missile targets were located inside the ship, underneath the armour. To reload, the fully retractable turret would descend down into its stowage space below the vessel's armoured hull, where the empty missile box, acting similarly to a magazine, was swapped out for a fully loaded one. This dramatically increased loading times over more conventional methods and provided protection for the turret and explosive ammunition during their vulnerable reloading cycle. Typically a turret could go from just having fired its last missile to having a full load in under 25 seconds. Inside the ship, there were different types of 'boxes' holding different missiles. These were selected according to the type of enemy the turret was tasked with engaging. The fire control room was located inside the vessel out of harm's way, but control could be transferred to a remote station inside the ship, or given over to an AI or dedicated weapon program which could select targets, fire the weapon and reload it independently.

Point/Area Defence Armament
Augmenting the Celestia-class' power were 35 M252 Area/Point Defence Weapon Systems, which could engage starfighters and very quickly destroy them. They offered both point and area defence against starfighters and incoming projectiles, and proved highly effective against larger targets in numbers, such as frigates, destroyers and some cruisers. The weapons were comprised of three DX52 Particle Cannons, arranged in a triple battery. The weapon had a range of 4 million kilometres, and a combined power of 7,500 terajoules, enough to tear through ship armour and vaporise starfighters.

In addition to these were 40 M253 Area/Point Defence Weapon Systems. These were fast-tracking armoured turrets mounting quadruple DP41 Light Particle Cannons. These were extremely effective against incoming ordnance, such as missiles and projectiles. As a secondary function they could engage and destroy fighters, but were not individually capable of posing a threat to vessels larger than frigates. They had a range of 250,000km, and a combined rate of fire of 5,200 shots per minute. Their combined power output was roughly half that of the M252, though in a continuous stream of shots instead of one large blast.

Supplementing these systems were 30 M56 Point Defense Weapon Systems. These acted as the final, smallest tier of defence for the vessel. They were adept at interception of incoming torpedoes, missiles, shells and other projectiles, being destroyed by the M56 before they could reach the ship. They were largely ineffective against fighters and larger vessels and so mainly were reserved for smaller targets.

As a general armament, the Celestia-class also mounted 32 dual M421 General Purpose Cannons. These were a variable light armament capable of defensive or offensive fire. They were able to fire a wide range of ammunition types, from RAPID, HEPAB, APFSTDS, HPSDAP, HPHE, HEPA and HVS/AP-HE, and could engage both small and large, armoured and unarmoured targets. The M421's primary usage was as a light, short range multirole weapon for warships of many classes. They could engage fighters, close range armour and incoming ordnance equally effectively, though were useless against many larger vessels. They could provide covering fire and suppression for other weapons, either larger and more powerful ones or smaller and more numerous ones. They supported other weapons in combat, by engaging any targets within their range and aiding in point and area defence.

The turrets were comprised of two L120 Freebore Pneumatic Effect Cannons. These were mounted onto a heavily modified Crusader turret, which had the insides gutted and the turret widened to accommodate an extra gun. This was mounted onto a fast-tracking turret with a 360 degree field of fire, and 165 degree elevation.

Other Systems
Some examples of the Celestia-class were equipped with a MWX02 GATEKEEPER Mk VI device. This was a scaled-down, reverse engineered iteration of the Forerunner's Halos, intended for small-scale tactical usage instead of large-scale strategic usage. The weapon was primarily used to quickly defeat large Swarm naval forces, thus negating their numerical advantage. However, as with the Forerunner's dealing with the Flood, sometimes the weapon was used for a darker purpose. If necessary, it could be used to wipe out sentient life on a planet, thus preventing the population falling into the hands of the Swarm for their own uses, including reproduction. The usage of such a destructive weapon was controversial, but necessary in the face of a superior and terrifying enemy. The device had a range of around 100 million kilometres, and was issued to one vessel in each battlegroup. Like the Halos, the vessel itself was immune to the weapon's effects, though the device would kill all sentient life within its radius, indiscriminate of their faction, species or affiliation. Allied vessels would encase themselves in a slipspace 'bubble' temporarily to protect themselves from the device's effects, though this process was lengthy and often not accomplishable during battle conditions.

The Celestia-class was also equipped with a HALO Pod Launcher, which allowed the rapid and covert precision deployment of troops behind enemy lines. This was crucial to the Celestia's role as a ground attack and support ship, allowing it to more easily accomplish its mission objectives. In addition, it was equipped with six HURRICANE Pod Launchers which allowed it to quickly and precisely deploy defensive turrets, vehicles, troops and supplies to units on the ground, again supplementing it in its role of ground support.

Shielding
For primary protection against enemy fire, the Celestia-class was equipped with six Avalon Orbital DWX/S 9012 Shield Generators. These provided a combined protection of 70,000,000,000 terajoules bombardment per second. This shield was an ovular 'bubble' which encapsulated the warship, maximising the power of the shield by minimising surface area. The shield generators were standard Type I Protective Energy Barriers, the most common and all-round type of shield. The shield was split up into six main sectors; forward, aft, port starboard, ventral and dorsal. Each sector was allocated a certain amount of energy corresponding to the amount of fire they were taking. In addition, these sectors themselves were split up into a grid of several thousand individual squares. Power could be redirected from areas under the least attack to those that needed it most, though this of course resulted in another part of the ship becoming more vulnerable. The shields were one of the most energy-intensive components of the vessel's energy requirements, taking up a sizeable percentage of the generator's output.

Unlike the shields of the Sangheili and other races, Allegiance shields were operated by creating layers of energetic distortion containing a high concentration of gravitons around the ship. This was several hundred times stronger than more conventional methods and was far more efficient at dissipating highly focused energy or kinetic impacts. The primary shield provided extensive protection, but could not prevent smaller sized targets from slipping through. The Celestia-class also featured a secondary shielding system to counter this problem, providing close range protection whilst also improving structural integrity. This shield was contoured to the exact shape of the hull, though projected a few molecules underneath it. The field was then extended outwards, increasing the structural integrity by several times. The field was projected by two additional DWX/S 9012 Generators, which were solely used for this shield. As a result it had resistance of one third that of the main shield, as it was not expected to receive heavy weapon fire in the same way.

The Celestia-class also featured a third shield, a Type II Protective Energy Barrier. The type II was an energy field protecting specifically against concussive forces and kinetic energy, thereby supplementing the main shield. To create the field, numerous anticoncussion projectors honeycombed the interior of the ship. When activated, the combined field dramatically improved the integrity of floors, walls, ceilings and other internal surfaces, as well as drastically increasing the strength of external ones. The projector's bubble-shaped magnetic fields created a single cohesive anticoncussion field that absorbed and dispersed kinetic energy and was powerful enough to render blasts, collisions, and other impacts inert. It was also highly effective against the magnetic acceleration weapons used by The Swarm, which were very destructive. The Celestia-class featured forty two DSP54 Anti-Concussion Field Projectors, independent field projectors that together made up the defence system.

Armour
As the primary armour system used by the Celestia-class, the vessel made use of an advanced new technology called ERA or Energy Regenerative Armour. ERA consisted of two layers of armour. The first was an energy-ablative, superconductive metamaterial layer. This layer effectively trapped almost all of the energy from enemy fire, whether that be kinetic, chemical or others. While not providing the perfect defence, its primary function was to feed this energy to the layer below. This was a variable property, energy reactive layer of extremely advanced nanomaterial whose properties changed when exposed to massive energy. In short, the armour became stronger when under fire. This extremely adaptable and useful ability stemmed largely from the Forerunners, who employed a similar technology in their Keyships, renowned for their ability to withstand concentrated, localised fire even without shielding. This technology was only successfully reverse-engineered in 2642.

The secondary layer relied upon the primary layer functioning efficiently for it to operate. As protection was only a secondary function for the primary layer of armour, it did not have an incredible resistance to enemy fire, leaving that to the lower levels. As a result, over time the effectiveness of the first and second layers decreased. The more damage the primary layer took, the less effective the second layer was. Eventually, after heavy and concentrated fire, the effectiveness of these layers was rendered nil. However, units armoured with ERA rarely exposed themselves to so much fire to allow this to happen, only rarely occurring in extended and intensive combat arenas. ERA was employed on all Allegiance warship designs from 2651 onwards. While its power requirements were easily met by the huge Zero-Point Generator the Celestia-class relied upon for power, it also offered huge advantages when engaging in combat with other spacecraft. It could splinter MAC rounds, shrug off high explosive and armour piercing rounds and harmlessly absorb directed energy weapons. When antimatter and nuclear weapons were used against ERA, the resulting energy increased the impregnability of the armour by several hundred times. However, it was very occasionally possible to overload the armour by concentrated antimatter weapons or directed energy weapons of a colossal scale.

It was only ever used as an addition to more conventional armour technologies, for instance ACE Armour. As ERA was dependent on energy sources and was only effective with strong armour layers underneath, vehicles only capable of mounting ERA or ACE usually chose the latter for its low maintenance and reliability, not to mention its non-existant energy requirements.

Underneath these primary protective layers were more conventional armour materials, which, underneath the removable first two layers, were modular and easily replaced. They were part of an armour technology system called ACE Armour, or Advanced Composite Endurance Armour.

The ACE Armour system was several layers of advanced materials, combining to form an incredibly resilient composite. It was capable of surviving devastating and extended hostile fire, and was equally effective against directed energy weapons, ballistics and explosive weapons. The Celestia-class employed a modified version to allow it superior protection when facing enemies in naval combat. Fighters and other single ships were armoured with lesser amounts, though still able to take heavy damage before exposing the craft to danger. It also offered huge advantages when engaging in combat with other spacecraft. In large enough amounts, such as on the Celestia-class, it could splinter MAC rounds, shrug off high explosive and armour piercing rounds and harmlessly absorb and dissipate even the largest directed energy weapons.

The first layer of the composite modular armour helped hold the outer armour together, and allowed some slight flexibility yet superior density to engage various threats. Resin-impregnated carbon nanotube fabric was wrapped around the composite armour to allow the best protection and structural strength. Below the outer layer was the primary defense in the event the energy-ablative armour was penetrated; a single piece poured Ceramic DCP plate.

The Ceramic Plate was sandwiched between two plates of CVT (Chromium Vanadium Tungsten) and Austenitic Steel alloy. The whole assembly then underwent a triaxial-prestressing method in which the preformed, porous ceramic material was soaked in a bath of molten metal, resulting in super-dense material. As the metal cooled, the composite of three plates (one of ceramic, and two of alloy) compressed, increasing both the density and compressibility of the composite dramatically. This process worked at relatively low temperatures and therefore was more economical than most comparative methods. The resulting compound could be molded into complex shapes and offered improved protection at significantly lower weight. This by itself was rather effective but was only secondary to the ablative layers and was superseded by other armour layers beneath.

Below the outer plate were several overlapping Ceramic chevron-shaped panels. These chevrons forced any round that happened to penetrate the outer plate to then penetrate the chevrons at a much higher oblique angle than the outer plate. This increased the armour's effectiveness not only by changing the penetrator's vector, but by increasing the thickness it had to penetrate before reaching the interior and disrupting even tandem warheads and delayed timer high explosive rounds. These chevrons were suspended in an elasticised rubber-like polymer that reduced the shock to the overall plate and transferred much of the impact energy outwards, reducing the stresses on the impact plates and feeding the energy-reactive armour layers. This material also helped break up penetrating HEAT warheads and KE penetrators by causing the chevrons to move around under the force of impact, deforming it and degrading its overall performance. In addition, it provided a reliable defence against HESH rounds, which were still in utilised despite a decline in usage.

Backing the composite materials was a second composite Alloy/Ceramic plate forcing the penetrator to again punch its way through at a different vector, forcing the round to fold or break up before it can defeat the final plate. The whole composite was then sealed in a wrap of carbon nanotube fibres to absorb any remaining spall and attached to the non-modular, base armour of the Celestia-class's hull in sections for easy replacement.

The underlying, non-modular base armour for the Celestia-class was produced using a process in which sets of inexpensive, thermodynamically compatible ceramic powders (Boron Carbide and Titanium Carbide) were blended with thermoplastic polymer binders, then co-extruded to form a fibre. This fibre composite was first braided then woven into the shape of the desired component. The fabricated component was then stacked and pyrolyzed to remove the polymer binder and hot-pressed to obtain the base preformed ceramic material for final processing.

This preformed ceramic matrix was still somewhat porous, and, though it was extremely hard and rather ductile, it was still rather fragile. The preform was then soaked in a liquid metal alloy bath. The preform absorbed the liquid metal, which then reacted with the ceramic powder to form a new ceramic compound that filled in pore spaces. The result was a plate with a larger internal solid volume, but the exact same external shape and dimensions as the original preform. This method required reaction temperatures of only around 1,300°C, compared to the 2,000°C required for traditional methods to form high melting point covalently-bonded ceramics. Because the final plate maintained the shape of the original porous ceramic, the need for post-process reshaping was removed.

Following this, the material was condensed using gravitational field manipulation, achieving a 82% smaller material for the same weight. This was done by 'stacking' layers of atoms as densely as the laws of physics could permit, and laminating them above another thin film that was as strong, but 'phase shifted'. This meant that the material was much more usable and more resistant to enemy attacks. The material was alternated in layers between these, producing a more resilient material, meaning that kinetic and chemical weapons had no effect on the material. The finished composite was extremely dense, lightweight, and was ductile enough to resist severe impact stress, while providing excellent thermal properties, and being easy to manufacture and replace when installed in a modular system.

Afterwards, the material was softened, or in some cases (where then material was composed of few or no individual components) liquefied by ion fusers. Then, as the resulting alloy cooled, it was bombarded by charged-particle vibrating waves. This dramatically improved the bonding strength of the molecules and gave the armor incredible resiliency. This again contributed to the sheer impenetrability of ACE Armour.

Underneath this, the Celestia-class also mounted an extra layer to allow it better survivability in spatial combat. This was a layer of Titanium carbide, impregnated with latticed neutronium filaments, a microscopic latticework of strands throughout the metal alloy. This was coupled with a layer of boron nitride, which could withstand almost any assault and protected the ship from dangerous radiation emitted from many celestial bodies, as well as the thermal energy generated from the ship’s re-entry into atmosphere. This final dual layer increased the structural integrity of the ship and allowed it to remain intact despite any heavy bombardments or gravitational forces that the ship may be exposed to. It also acted as the base armour of the vessel, its last line of defence before the hull was breached.

Engines
For sublight propulsion, the Celestia-class employed a tandem engine layout. It employed four ion thruster pods to provide low sublight speeds, as well as sole propulsion in atmosphere. The drives provided a rapid acceleration, which made them useful for slower evasive actions and movement in atmospheric conditions. However, they had a relatively low top speed, of around 12,000kph.

The concept of Ion Drives was nothing new, and most spacefaring vessels employed a similar such system. Propellant gas was passed through an alternating electric field, ionising the gas. It was then expelled out of the engines at near the speed of light. The electric field used was massive in terms of power, meaning higher efficiency and less propellant gas needed. The colossal power for the field came from the near-limitless amounts of energy generated by the zero-point reactor.

For higher sublight speeds, the Celestia-class utilised two integral Graviton Drives, which, although were much slower accelerating than ion drives, had a hugely different top speed. Their top speed was near 20% the speed of light, though speeds of more than 5% were rarely used due to the associated relativistic effects. When going at higher speeds, the ion drives were used to quickly accelerate the ship to the drive's maximum speed, where the graviton drives took over for a slower acceleration and higher top speed.

These Graviton Drives used a much more advanced method of propulsion. Using graviton manipulation, they were able to slowly achieve unheard of speeds, though at the expense of fast acceleration.

The Celestia-class also possessed numerous anti-gravity engines which allowed it to hover in-atmosphere. These engines were similar, though more advanced, to the ones employed by the Covenant, which were reverse-engineered from Forerunner engines. The ship was specifically refitted for prolonged operations in atmosphere and was capable of indefinite atmospheric operation.

Powerplant
The enormous power requirements for the Celestia-class Assault Ship were met with an equally enormous energy source. Providing power to the vessel was one Strategic Instruments ZPM/A-860 Zero Point Generator, manufactured solely for military usage. Zero-Point generators extracted vacuum energy from a small artificially-created region of slipspace, in order to produce powerful energy from an efficient source. In physics, zero-point energy was the lowest possible energy that a quantum mechanical physical system may possess and was the energy of the ground state of the system. The generator produced 7.445 x 1025 Watts, or 74,450,000,000 Petawatts, of energy, one Watt being one joule per second.

The generator was located a few hundred meters aft of the command centre, both sharing the least vulnerable location in the ship. The reactor took the form of a semi-spherical chamber with the generator core in the centre and struts forking symmetrically in.

The vessel had no secondary power facility, and relied on vast energy storage devices to keep the ship even remotely operational in the event of a generator failure. Without this, the ship was completely inoperable. While powered by the energy storage devices, only essential systems could be powered; life support, artificial gravity and sublight/FTL engines taking precedent over shields, weapons and sensors.

Complement
Arguably one of the most potent features of the Celestia-class Assault Ship was its ability to carry huge numbers of fighter craft. A single vessel alone could bring eighteen full fighter squadrons, a total of 216 fighters. Vessels very often carried multiple types of fighter, adding to the versatility of the vessel's assigned air wing. This number of fighters was sufficient to provide huge support to ground forces, or to provide services in space. It was during exoatmospheric operations, however, that the Celestia-class' fighters came into their own. They could provide a starfighter interdiction screen, protecting allied vessels and preventing enemy single ships reaching them. They could engage enemy capital ships and, in large enough numbers, overwhelm them. In short, they provided a valuable and vital service to both the ship itself, and any accompanying ground or naval forces, to such a degree that they often turned the tide of battles.

The most common setup of fighter craft within the Celestia-class Assault Ships was as follows:


 * 9 AL-56 Flashfighter/AL-61 Valiants Light Fighter squadrons
 * 6 F-307 Blackbird Medium Fighter squadrons
 * 4 F/A-240 Scythe Heavy Fighter squadrons
 * 1 X330 Shadow Stealth Fighter squadron

The Celestia could also carry older fighters, such as the heavily outdated AF32 Starstreak. However, their numbers dwindled towards the end of the 27th century and were rarely seen in combat, being more suitable for museums. Commonly the ship would deploy the majority of fighters and keep two squadrons behind as reserves. The ship's most senior pilot, the 'CAG' or Commander, Air Group, was in command of the vessel's embarked combat craft, which was restricted to fighter and bomber complements.

The Celestia-class also carried a large number of bomber craft. It could carry up to 6 bomber squadrons, or a total of 48 craft. These were generally a mix of the AH-17 Raptor spatial bomber and the more atmospheric-capable R41 Phoenix. As the war dragged on, newer bomber classes began to replace these in ship complements. Towards the latter days of the war it was not uncommon for a ship to be equipped with a random assortment of fighter and bomber craft, vessels and fleets willing to accept whatever craft they were offered.

After 2774, the Celestia-class was gradually equipped with the newer and more advanced BH-21 Valkyrie bombers, instead of the older Raptor. This considerably increased the potency of the Celestia-class' starfighter complement and enabled stronger power projection and support when engaging larger targets.

The Celestia-class' bomber squadrons were employed to carry out support to larger vessels, and destruction of large armoured targets in space, as well as precision target demolition in atmospheric conditions. They provided a valuable and important anti-armour support to the Celestia-class Assault Assault Ship under combat conditions. For transport and support duties, the Celestia-class was equipped with forty ATL-772 Sabre Dropships. They were tasked with ferrying the ship's troop complement to groundside combat, providing close in air support to ground forces, and for transport between allied vessels. Some of these were usually swapped out for AS70 Nighthawks, stealth infiltration dropships for boarding enemy vessels and transporting troops behind enemy lines.

Providing heavy lift and transport were the Celestia's complement of eight CT-40 Vanguard Heavy Transports. These primarily non-combat craft could ferry the Celestia's vehicular force to combat on a planet's surface, having huge capacity and endurance but little else besides. Nevertheless they were an important part of the Celestia-class' status as an assault ship, rather than a cruiser; its designation stating the ability to support friendly and to assault enemy ground units.

Introduction and Early Years
Introduced in 2429, the Celestia-class Assault Ship saw more action reinforcing the Allegiance Navy's supremacy after its severe weakening during the Reformation War, rather than actual engaging enemy naval forces in combat. As a result of being deployed frequently to areas of civil unrest, the class gained a reputation for being the projection of the Allegiance's power, and a powerful psychological deterrent to any who might oppose it.

The class' first proper naval engagement, however, was the Third Battle of Earth, in which the shocked Covenant forces attempted to strike revenge on humanity for the event on the Ark in early 2553. Twenty four Celestia-class vessels made up the bulk of the Allegiance defence of the planet, and, with assistance from the severely depleted UNSC Home Fleet, defeated a Covenant fleet of almost five times the size that of the defenders. The class saw extended and successful combat against various Covenant splinter factions in the years 2553-59, amassing a fearful reputation among ally and enemy alike. The Battle of Dosiac saw the near-permanent crippling of those of the Covenant still loyal to the Great Journey, and to the war against Humanity. The class saw exemplary performance during the battle, though it arguably marked the peak of their service.

Later Service
In 2593, the class was converted to armed freighters. The Celestia-class was perfect for the role; it was well armoured, faster than most other freighters of similar tonnages, was well armed, and, most importantly, had a large cargo capacity. These vessels had their flight decks sealed off and pressurised, creating enormous, rudimentary cargo holds. These were in addition to all the fighter storage, vehicle storage and troop space that was repurposed for cargo, on top of the existing cargo space that was available for storage. Being a former cruiser, the ship also benefited from powerful military-grade engines that allowed it to compete with other vessels in engagements, thrusters of the kind that just weren't available to mere armed freighters. On top of that, it was rather heavily armoured, although some of the armour was removed to lighten the vessel. Its armament was reduced by roughly a third, easing crew requirements and making the vessel less hardware-reliant. The Celestia-class Freighters, as they were now called, were often found as escorts to unarmed cargo vessels in hazardous places or times, where proper armed warships were unnecessary or unavailable. As a result, some examples of the Celestia-class could often be seen accompanying large fleets of smaller vessels. These protected fleets were of great value to both the UNSC and the Sangheili, as they allowed trade to continue between them relatively unhindered by rebels, pirates or dissident Covenant forces. However, many saw the class's extensive downgrading as the twilight years of the Celestia-class, seeing no way a class so old already could continue serving much longer.

Refit and Swarm War
However, the Celestia-class was still serving in this role by 2700, more than a hundred years on. This was a combination of the low demand for an armed freighter, and the class's superb filling of the role. The Swarm War, which commenced in 2733 and dragged on into the late 2800s, severely drained the Allegiance's naval power and forced it to put ships into battle any way it could, so pressed was it for vessels and fighter craft. Some saw it as ironic that the Celestia had arrived after one crisis and would now help in another, but the simple fact was that the class was a former cruiser, and very numerous within Allegiance space. The class was, in 2784, extensively and exhaustively overhauled and refitted, upgrading everything from shielding, engines, armour and weapons to reversing the changes to make it a freighter class and modernising its fighter handling facilities. By the time the class was re-introduced, it was not the most modern, but certainly one of the most formidable vessels fielded by the Allegiance, helped to a large degree by its dual cruiser/carrier nature and its ground support ability, able to go toe-to-toe with some of the newest ship designs on both sides of the war.

During the Swarm War, the Celestia-class participated in almost every major battle of the later war period, though was often sidelined in favour of more modern classes despite its performance record both old and recent. In later years, this option was no longer available, and the class was seen more prominently in Allegiance engagements with the Swarm. In addition, the class was extensively used for probes into enemy territory, often alone or in 'hunter-killer' pairs. The class played a part in the core world battles that occurred after 2800, such as the Battle of Britannia, the Battle of the Apollo System, the Battle of Haven and the famous Battle of Thera. From 2850 onwards, the Celestia-class no longer operated under the command of the Royal Navy, but was officially transferred along with the rest of the Allegiance's naval ships to the command of the Unified Coalition of Governments Navy.

Ships of the Line

 * HMS Celestia (class namesake)
 * HMS Columbia
 * HMS Galactica
 * HMS Atlantia
 * HMS Pegasus
 * HMS Solaria
 * HMS Valkyrie
 * ''HMS Atlas
 * ''HMS Cerberus
 * HMS Chronos

Trivia
The Celestia-class Assault Ship is based on the Galactica from the TV series Battlestar Galactica.