Abyssal Submarine

"The silent knife of the deep"

Combining the gathered knowledge of the deep sea expeditions on Iona as well as research taken from combating enemies of the Imperium in the depths, Pionus, in conjunction with the Magii of Forge World Kirya designed a complex attack submarine that would strike fear into the enemies of the Imperium. With many of Pionus' discoveries from the forgotten depths of Iona being incorporated into the submarines design it provides a platform, which came to be known as the **Abyssal Submarine**, capable of taking on entire fleets of vessels single-handedly and operating for a year at sea with no replenishment. This robust vessel has proven itself to be a capable and reliable member of the Scions Hospitalier armoury.

## History

After their liberation from the titanic Ke'Mano's tyrannical reign of the Yamatar Region by Pionus and several other legions the worlds therein owed them a great debt. The conclusion to this lead to Pionus working in tandem with the planetary governors of the region in an arrangement to make all the resources of the region available to the Primarch and his legion in the Ke'Manon Pact as well as the service of Legio Gojira and House Toho as steadfast allies. To this end a joint research and development team was created, comprising of 19th legion Techmarines and the Head Magii of Forge World Kirya, focusing their efforts into developing equipment and machinery to help aide the Imperium in the wars to come.

The Ke'Manon Pact solidified the focus between the two parties who, previously, might have found themselves playing the part of invader and defender. The bonds between these Magos and Techmarines having been forged in the same fire lead them to creating great works to do both the Mechanicum and Scions proud of, despite their difference in methods. Scions from across the galaxy equally shared the information gathered by their many delves into Terran and Martian archives as well as the archeotech found by the expeditionary fleets, most if not all finding their way back to those same labs on Kirya.

It was during this flourishing time that a particular Techmarine by the name of Gallas and his Mechanicus counterpart Raellix sent a missive to the upper echelons of the Forge world, with a proposal for a formidable war-machine. They had discovered an ancient STC design whilst exploring the ruins of one of the many hives decimated by the Ke'Mano, released from it's ancient resting place beneath the city. Together built a prototype based from this STC of a great submersible, presenting it before the Fabricator-General to display it's power and potential. Though the machine caused great disturbance during the display when it crashed into a motorway and collapsed it due to several errors within the motor-control cogitators, It had sufficiently impressed the Fabricator-general and his staff to allow them to continue.

Several years later the STC had been adapted and refined into a complex naval platform, replete with an arsenal of weapons and systems that allowed it to excel at striking almost anything it was put up against. Extensive demonstrations of it's accurate ability to scan, classify and destroy enemy vessels as well as it's ability to support amphibious operations impressed the Cybersmiths and Skitarii forces alike on Kirya but for it's final test Gallas requisitioned a more unorthodox challenge.

#### The Strength of the Anchor

On the Scion's home-world of Iona was the final test for the machine. Locked within a natural harbour 80km across, the last member of a Kranithus Cast, a vast armoured, crab-like leviathan -equivalent in size to a Reaver Titan- had been corralled. The beast, reluctant to leave the protection of the water and unable to leave due to the great charge-net's blocking the bay had simply wandered around. At the request of Gallas and the Fabricator-General of Kirya they had been tasked with using their new prototype to hunt down and kill the beast.
 The hunting of the beast posed a serious challenge to the fledgling vessel and her crew, sonar sets ticked at the slightest ocean noise while the patient hunters waited for the opportune moment to strike. And strike they did.
 After the beast's carcass floated gently to the surface, so to did the submarine, with Gallas and Raellix stepping out with pride. Partially to confirm the kill but in part to celebrate the years of work and effort that had gone into the project.

Their enthusiasm was rewarded as they watched the beast bobbing gently along the surface. Though, as the delegation from Kirya approached to congratulate them they both noticed the unmistakably large figure of a Primarch on the boat approaching them. Gallas' father, Primarch of the 19th congratulated them both, explaining that he had been following the project with great interest and managed to come back to Iona to assess the vessel himself. Humbled, the creators offered what little they could in return, the design of the vessel and the honour of naming it. Pionus accepted, looking to the ruined beast and under his feet, the new blade he had in his arsenal.

 *“To kill a creature of the abyss is proof enough that it's ready. In fact I like that. 'Abyssal' It's a good name, one that reminds the enemy that they shall be destroyed, and lost to the depths in both body and memory. I find that fits well, don't you think?”* **- Primarch Pionus Santor, upon the successful completion of the Abyssal-Class Submarine testing.**

 Wide adoption of the design led to the Abyssal making it's mark on many Scion campaigns throughout the galaxy. It's ability to survive for extended periods of time alone led to it conducting surgical strikes against many an undefended flank whilst it's ability to overwhelm coastal defences, whether directly or indirectly, led to it' being nicknamed the 'Deep Dagger' by those forces it fought alongside.

 The first major deployment of the Abyssal took place during the scouring of a string of ork worlds called the Galvan Ridge, controlled by BlazzAye Stormdrinka who had beset the worlds surrounding his small empire. The ramshackle fortresses of the Yellow Sun clan pockmarked the surface of each planet, hive cities turned to monuments of WAAAGGHH architecture and blasphemy as they turned the seas black with their promethium mining platforms. The crude fuelling their war machine allowed the Orks to spread to nearby systems, the heavily armoured Gargants and super-heavies being produced there expanding Stormdrinka's domain until expeditionary scouts brought his domain to the attention of the Master of the 19th.

#### The Purgation of Gaal

The campaign to rid the Ridge of the greenskin menace consisted of a three-pronged attack , two imperial army forces taking the outer worlds while the Scions sought to cut the head from the snake. Blockading the planet turned out to be  the easier part of the campaign as the Warboss' fleets had been forced elsewhere by the flanking attacks of the Imperial Army, but the planetary defences were another problem all together. The hive-cities and refinery platforms had extensive defensive weaponry, and deep armouries, as they launched salvo after salvo of missiles and laser blasts at the orbiting ships. This eventually forced the repositioning of the fleet to a much higher orbit, where the Ork's weapons could not reach, but their own weapons because similarly ineffective.

To solve this the leader of the 19th's forces, 17th Captain Meraxes, had to change strategy. While the bulk of his fleet stayed in high orbit over the planet he sent the bulk of his landers and transport craft to the uninhabited north pole, being that it's cold environs and lack of promethium deposits meant it was useless to the occupying Orks. This force landed a full fleet of 60 Abyssal-Class vessels uninterrupted by the Greenskins. The submarines then sunk into the depths to do their quiet work as the transports returned to orbit unmolested. The Orks, not anticipating an attack from beneath the waves had simply neglected to set any sizeable defences such as minefields or sonar arrays to stop or even detect the submarines. From this advantageous position they proceeded to systematically dismantle the promethium refineries and any settlement inland their weapons could reach. Captain Meraxes simply watched from orbit as each of the Ork refineries and platforms blossomed into small pyre on his tactical display. With the majority of the world taken, the remaining Ork forces in the inland settlements began to grow nervous, their supplies cut off they slowly began to starve of oil, food and a good fight as the Scions used the Ork's own nature against them.

For three weeks the Scions moved on small settlements, avoiding the large cities by a wide margin. They made as flashy a landing as possible at lone mekshops, small Ork Rok colonies and convoys. Taking their time decimating the outposts to allow the main Ork horde to tire themselves and their resources trying to catch up with the marines, but always at the last moment the Marines would simply retreat to orbit, safe from the oncoming horde. At daybreak on the 3rd week of the blockade the remaining Ork cities were in riot. With all their resources spent and not a single good fight they were tearing at themselves as a rabid beast might. It's thanks to this strategy that they proved a much simpler foe to defeat.

Captain Meraxes at the head of a force of 3000 marines cut their way through the diminished Ork Hive cities, eventually storming the keep of BlazzAye Stormdrinka, only to find his throne-room in disarray with several of his Lieutenants engaged in a bloody melee over the broken corpse of their Warboss. In their attempt to gain power they were all-together too occupied to notice the contingent of Depthstrider Terminators and their heavy weaponry, until they were little more than green stains on the throne room wall.

With the world caved from within by the Hospitaliers submarines and the Orks destroyed by in-fighting, it was a massively successful campaign which became part of the long list of victories attributed to the Scions -and specifically the Abyssal Submarine's- name.

Other campaigns have allowed the destructive power of the Abyssal to show it's full potential as with the Ork empire of the Galvan Ridge, using the silent and deadly nature of their design to full effect. The submarine has proven itself time and time again to be a core asset of any 19th Legion force that a Commander would be foolish to go without.

## Design

The design of the Abyssal stems from that long-hidden STC design found in the ruined wake of the Ke'Mano. A long, cylindrical body used to house all the necessary command and control, weapons, engine and support systems necessary for extended deployments underwater. The outer layer of the ship is covered in sound absorbent materials, with the nose tapering to a rounded point and the tail tapering into the 2 main propellers. A single fin is mounted on the dorsal side allowing for a commanding view when surfaces, and 4 horizontal control fins jut out from the body at regular intervals, with 2 on either side. The form is designed to use stealth as a weapon by hiding it's own signature as much as possible through shock-absorbing mountings  and multiple layers of noise-dampening armour and plating. Internally consisting of 4 distinct deck levels and 3 main sections  (The forward, mid and aft sections) the vessel is packed with everything necessary to support extended operations at sea. With the ability to operate for such a long time, the ability to strike virtually any target and directly support amphibious landings the Abyssal is the perfect multi-role naval platform to support Scion operations.

### Armament

#### Naval Weapons

 Designed first and foremost as a weapons platform the weaponry squeezed into the submarine's body makes sure it uses every square inch of space to fit as much firepower as possible. Able to track hunt and kill enemies within the sea and able to bombard fortified positions from the safety of the sea provides the biggest advantage of all.
 The traditional submarine weapon of torpedoes are present, with 6 launch tubes located in the 'chin' of the ship supported by the weapons bay any good team can reload a full salvo of torpedoes in less than 3 minutes. The weapons bay, where all 48 spare Typhoon torpedoes are stored, has a complex system of lifts and racks, allowing for the maximum storage area and swift reloading of empty tubes.

 The Typhoon torpedoes themselves are a modular weapons platform. While the main body is powered by both a small multi-fuel combustion engine the warhead itself is variable able to swap out the normal warhead for a plasma or even burrowing 'Rikkter' melta payload. Able to be controlled remotely by wire or using the on-board servitor cogitation system to search for targets, it guarantees to find it's prey.

 The other main weapon system aboard the vessel takes up a large amount of space in the midsection, stretching down several decks it is the main anti-surface and anti-air capable weapon whilst at sea. 16 launch cells are placed vertically along the spine of the ship, able to be launched from underneath the water itself they can house 2 main form of munitions adapted from Imperial Guard and Navy variants.

 The first weapon is a long-range missile similar to that of the Manticore tank used in the Imperial Guard. A large missile capable to striking long-distance targets with extreme accuracy, either guided by spotters on the ground or through targeting information fed into it pre-launch. The weapons warhead system is also modular, allowing for quick changes as demanded by the mission profile, whether that be bunker-busting, precision strikes or atomic annihilation. Due to it's high-speeds achieved by the rocket motor propulsion, an upgraded guidance system allowing it to fly at very low altitudes to avoid radar detection and the variable warheads that can be mounted, the missile, dubbed The Sea-Scythe, while limited in capacity, more than makes up for it in tactical flexibility.

 To round out the idea of 'tactical flexibility' in the Abyssal platform each missile cell has the ability to house anti-air missiles as well, though, due to them being smaller in size, 4 can be fitted into one. Each of the Dominae missiles has complex radar detections systems as well as a set of manoeuvring thrusters normally reserved for void vessels and weaponry. The addition of these thrusters allows the missile to make lightning-quick turns to hunt down and attack aircraft from an optimal angle.

#### Amphibious Landing Weapons

 With the ability to move onto land and support amphibious operations thanks to the STC designs recovered from Kiryan ruins, the Abyssal has several turrets held on retractable mountings that can be deployed to lay down extreme amounts of firepower on any coastal fortification. Each turret is held on a baseplate capable of 360 degree rotation that can be lowered underneath the outer layer of the submarine when not in use. This retractable turret system allows the ship to remain stealth by not creating too much noise when in the water and allows small-scale maintenance to be performed when retracted fully. Each turret has a housing compartment that can be pressurised and drained down for the purposes of repair and maintenance and to limit exposure to the crushing pressures of the deep, which can interfere with weapon mechanisms.

 There are 4 specific turret mountings dotted over the body of the vessel to provide as much coverage as possible as the Abyssal is particularly slow when out of the water. There are two turret mounts on the top and bottom of the nose of the submarine, these each mount a pair of Accelerator Autocannons. The Accelerator Autocannons, being a heavier version of the standard Stygies pattern normally used on Predator tanks, is the result of a development programme lead by the Primarchs Nomus Sardauk, Daer'dd Niimkiikaa and a section of the Martian Mechanicus, along with a vehicle platform, namely the Sicaran tank.

 The final 2 turrets are much larger in configuration than the accelerator autocannon mountings, and are mounted on both flanks of the vessel, at the midway point along it's hull. Each has extensive systems of hydraulically controlled plates that allow the large mountings and the weapons themselves to be stowed and revealed. This complex system of plates also changes to accommodate the newly revealed weapon, enclosing around its base, allowing for full freedom of movement whilst covering the internal hull with the outer layer of armour.

 The weapon mounted on the large turrets consist of a single Turbo-Laser, connected directly to the submarine's reactor through several large capacitors to provide power. Each turret is fully manoeuvrable, able to track and engage targets anywhere within it's 180 degree arc of coverage. The turbolaser, being famously used within Titan Legio's in multiple-barrel configurations has been adapted to the Abyssal chassis in innovative ways thanks to the efforts of Magos Raellix. Through ingenious installation of redundant battery and capacitor systems as well as a super-cooling system lightens the power drain on the reactor as the weapons fire. This system is charged while not in combat and allows 12  individual discharges of the Turbolaser before needing to rely on the reactor to be charged up.

 The Turbolaser's destructive potential, even in a single-barrelled configuration is not to be taken lightly, able to carve it's way through super-heavy tank armour, burst void shielding and burrow holes dozens of metres deep into enemy fortifications. The energy weapon has proven to be the decisive blow that breaks open coastal defences allowing the Scions to storm the breach.

### Control Systems

 The submarine itself has to be entirely self-sufficient whilst at sea and therefore has to control the myriad systems that keep it operational, to do this there are several key command stations that oversee specific subsections.

 The Control Room is the central hub for operations, with multiple MIU capable units it allows the sub-systems to be controlled by a mixture of Hospitallier Tech Marines, chapter serfs and servitor stations to complete their tasks. These sub-stations include the sonar system, which detects, tracks, classifies and monitors any target vessels, the tactical station which handles weapons targeting and control of sea and land weaponry, communications, navigations and the like. The command throne of the vessel itself is placed at the rear of the control room with several heavy MIU links embedded in the chair's surface, allowing it to intake large amounts of information and even allow the Captain to override subsystems if necessary.

 A secondary control room is located in the rear of the vessel above the engineerium control room for redundancy. The engineerium itself is heavily laced with thick cabling and panels of monitoring systems and switches which allow the crew to monitor and distribute power from the reactor throughout the ship as they see fit.

### Defensive Systems

 The hull of the Abyssal is separated into two distinct sections, the outer hull an the inner hull. The inner hull is a thick layer of adamantium plating and is the vessel within which the crew and the ships systems are contained, while the outer hull is a mixed layer of sound-dampening tiles, ceramite plate with armaplas mesh over a thinner adamantium hull. The outer layer is developed so that it can maintain a quiet profile whilst in the water and provide adequate armour to the ship as the differing types of armour used means it is more likely to defeat weapons used against it. In the case the outer hull isn't enough to protect the ship the fallback of a thick layer of adamantium allows the Abyssal to weather anything short of titan weaponry before it retreats from a fight.
     Placed underneath the outer hull at regular intervals are small, single-launch tubes, each loaded with a 'Siren' Pattern of naval decoy. These decoys are used against guided naval weapons or simply as a screen to allow the Abyssal to retreat behind. The decoys work by generating a massive amount of noise that varies frequency, whilst also making large clouds of bubbles through rapid heating of the water around it. This distraction means that any guided device wouldn't be able to hear, see or detect (through thermal imaging) the submarine whilst a siren is deployed.
     The major defensive system in place on the submarine takes up the rest of the space in the nose of the craft not occupied by the torpedo tubes and storage bay. A single large void shield generator along with support cooling systems are connected through hundreds of metres of cables and piping to the reactor, feeding it with all the energy needed to keep the shield functioning during amphibious support operations. The unique thing about the shield is that when activated it is used as a focused area rather than an all-encompassing bubble, only manifesting to cover a 150 degree arc. While this arc provides much less coverage it can be strengthened significantly and is able to be directed anywhere in a 270 degree arc, and used to defend against specific enemies that appear, rather than using more energy to defend against threats that would easily bounce off the submarine's hull armour.

### Engines

The reactor that is needed to power the Abyssal beast is one of particular interest, a heavily copied design from the Titan-factories on Kirya it is the beating heart of the vessel, able to power the submarines systems even under a heavy load. While the original design was taken from a Warlord Class a few alterations were made to suit it's environment. A heavier layer of shielding is used around the reactor section of the submarine, consisting of heavy adamantium plates and large water tanks to block escaping radiation. These water tanks also provide an alternate fuel source to the already formidable reactor. By directly taking in water from the ocean it is then separated into it's baser elements of oxygen and hydrogen through electrolyses, both of which are of great use on board. The oxygen is used to replenish the air on board, allowing the submarine to stay submerged without having to come up for air (More commonly referred to as 'snorkelling') The hydrogen however, is condensed and stored, and can be 'injected' into the reactor itself to increase the power output of the reactor temporarily. This 'injection' is rarely used as it increases the demand on all of the support and piping systems of the reactor, and can in some cases render  the reactor, inoperable and need to go into dock for repairs.

In the case the reactor is unavailable there are batteries that provide a limited amount of power. These are usually used when the need for stealth is utmost, the reactor is lowered to it's minimum power output, thereby lowering noise, and the submarine can move past even the most sensitive of detection equipment and mines without effort.

### Miscellaneous

 An element of the vessel's design was implemented after several of the initial designs released reported problems when it came to damage control, specifically, fires. It was swiftly found out that if there was any fire inside the vessel the smoke and heat would quickly spread, leading to whole sections needing to be quarantined until damage control teams could deal with the problem.

 To solve this problem the internal layout was given redesign, that saw the large sections being split into smaller ones, with more bulkheads to help contain any fire in a small area, rather than having to seal off the entire mid-section until a Damage Control team could re-enter and subdue the fire.

 The crew of such a complex and important military asset would normally be entirely made up of marines from the Scion's ranks, but due to the tight fit between so much machinery and miscellaneous job roles necessary, highly-trained mortals are used to fill the gaps. The vessel is commanded by a Scion's Captain, and supported by 2 Techmarines who oversee the function and maintenance of the equipment (One fwd, the other aft) 6 more marines are used, both as officers for the mortal troops and as the ship's protection force in the unlikely case they are boarded. The mortals themselves are split amongst engineering, warfare and support cadre's with each group working to help the ship operate at maximum efficiency.

 It is widely known amongst the Imperium that mortals and transhumans tend to have a large barrier between them in terms of experience and mindset, but it has been noted amongst those Abyssal crews have a much higher rate of integration between the two parties. This is speculated to be from the close living conditions, extended periods isolated at sea and the need for cooperation, the unique environment breeding loyalty, trust and respect amongst those who serve long patrols together.

 To deal with the inevitable occurrence of damage to internal systems, the breakout of fires or major malfunction of any equipment, teams of mortal sailors are trained as Damage Control Teams under the command of the Techmarines and Magii on board. Given basic knowledge of equipment functions and guided by the overseers they don heavy flame-retardant bodysuits lined with a low-grade exoskeleton suit, rebreathers masks and Extinguisher cannons. In the case of more serious problems such as the hull being blown open or the reactor itself, that is taken on by the Techmarines and Magii due to their increased resilience and engineering knowledge.

 In the unlikely event that the ship is boarded, whether at sea or docked the crew have a dedicated team of both marines and mortals to respond to the intruders as the Ships Protection Force. Due to the more enclosed space, full Astartes power armour is very limiting in it's bulk. In place a set of thinner ceramite plates are used, covering the legs, arms and chest, not requiring the power-plant backpack. Alongside the lightweight armour is a rounded boarding shield  with a weapon slit (formed to the same shape as the hatches between compartments) The design making it very easy to block incoming fire whilst suppressing an enemy in the next compartment. In support of the marines is the mortal contingent of the Ships Protection Force, armed with heavy carapace armour and automatic shotguns to reduce the risk of a fire during combat.

 The final, and most important element of the Abyssal's arsenal of tools is it's ability to go from a sea-faring vessel, to one that can walk on land. Found amongst the rubble of Kirya in one of it's many failures against the Ke'Mano by Magos Raellix, a chassis of ancient and unique design hidden away amongst the titan forges. This chassis, almost as tall as a Reaver at it's full height, rather than being humanoid was more insectile in it's design, and was swiftly herded away to the Magos' labs to become part of the Abyssal project.

 4 separate sets of finely tuned legs are housed in the outer shell of the submarine. Flush with the hull, these legs allow the vessel to travel through the water with minimal resistance and some sections can be accessed and have maintenance performed from within the hull itself. When needed, the legs stretch out from the hull, and slowly take the weight of the vessel until it is standing unaided by the buoyancy of the sea, and can stride onto land. The main use for this particular asset is to allow the Abyssal to support coastal assaults, able to follow the Scions as they rise out of the water by laying down massive amounts of weapons fire upon coastal defences. This has proven massively effective as the size and weaponry available with an Abyssal Class rivals that of a Warhound titan, something most coastal defences are ill-equipped to defend against. The only downside to the amphibious capabilities is the speed of the system, the legs are notoriously slow and ponderous moving the vessel once it's on land, meaning it can easily be out-manoeuvred and out-flanked if an enemy is quick enough to respond. For this reason they are only used to support coastal assaults before fading back into the ocean, as land warfare would see their slow speed easily taken advantage of.

## Notable Abyssal Class Submarines

* ***Astute Edge*** – Abyssal Class Commanded by Captain Selias of the Scions Hospitalier 42nd Fleet.

* ***Horatian Command*** – Abyssal Class Commanded by Captain Forall Thunderhead of the Scions Hospitalier 7th Fleet.

* ***Guiding Current*** – Abyssal Class Commanded by Captain Tomhi Wayso of the Scions Hospitalier 27th Fleet.

## Notable Variants: Atlas Transport Support Submarine

(*See Main Article:**Atlas Transport Support Submarine***)