Have fun. Just know that I dont really go over the stuff I read and correct it. Its very much Freshly Written -> Submitted 
Side Note; Iona is a water world that is 40% Larger than Earth with its deepest point, the Odyssian Trench, being 1.2k Kilometers below the Surface.
Some art pieces that illustrate the type of environment:
BLARGH GIANT WALL OF TEXT:
Segmentum Tempestus
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Irritum Mare System
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Iona
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Sub Aquatic Bay Primus, Sector Gamma, Hive Atla
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800 Kilometers Below Sea Level
Its horrendously humid, thought Daer'dd. And surprisingly cold too. Though these kinds of thoughts were usually of little to no concern of his given his usual line of work and neither were they capable of causing him any trouble due to his very nature, its in rare moments such as this where, bereft of anything to do, that he just...thought. It was moments like these, that he enjoyed the most for they reminded him that he was, as his core, human and at peace.
Daer'dd's thoughts would follow a myriad lines of thinking similar to these as he stood waiting, staring out into the black, watery abyss on the other side of the Multi-Meter thick Synthglass Viewports, his Honor Guard standing near him, content to leave him to his reveries. How closely this resembled the endless void of space, he thought, sighing.
Behind him, Legion Serfs, Techmarines and other members of his Brothers Legion were working away prepping the three Vehicles that would carry them to the Hunting Grounds. Turning around to survey the work being carried out, he inspected the three vehicles.
They were clearly Storm Eagles or at least based on the chassis, that much he could tell but, apart from a similar profile, thats where the similarities ended. The Phaeton Pattern, the name given to him when he asked the Techmarine in charge exactly what they were, were peculiar vehicles. While the standard Storm Eagle was a void Capable Craft, it stands to reason that they weren't capable of standing up to the pressures present so far below the surface for this craft was noticeably bulkier than normal, the sign of a reinforced frame and structure most likely.
Additionally, they lacked a Forward or Rear Ramps instead having two elongated side hatches that ran the length of the vehicle and one that ran the length of the Phaetons Floor; the use for which he'd probably figure out during the hunt. Speaking of Front and Rear Ramps, he thought, these mounted Ball Turrets in their place, much like the Fire Raptors they all had in their Legions Armories though, he reasoned, that these probably mounted Volkite Weapons due to the unreliable nature of bullets in aquatic environments. Finally, and possibly the most striking of its features were its generally more rounded Features. While its true that shape held no real impact on void maneuvering and anything could fly under normal atmospheric conditions given enough thrust and lift, the stresses non-aerodynamic or smoothed surfaces would suffer when moving at high speeds underwater were probably enough to warrant such a drastic redesign of the general shape.
Thats as far as his knowledge as a Smith got him, however. How the vehicles engines could propel it underwater without being propellers, he could only guess at. His knowledge of the esoteric going only so far. Still, they were interesting craft. Probably another of his Brothers Scientific Achievements.
Out of the Corner of his eye, he spotted movement. Turning back to face the viewport he caught a glimpse of a tail, scaled and massive fading into the inky blackness. An Omen of things to come? he Wondered. He turned to inspect his equipment in their storage racks beside him. He had decided to remain unarmored down here, wanting to get out of his battle plate for at least a few hours. It stood in its transport case off to one side the Helmet he usually eschewed present for all his Post-Human might, he could not still breathe water...Pionus though, he wondered. His Gauntlets were in their own case at the foot of his armors, resting in a portable stasis field. He opted to bring his throwing Axes anyways. While he would not have been able to use them as such, having a bladed weapon could prove useful. On a Small Rack beside the Armor Case was his Volkite Caliver. Pionus had specifically asked that he bring an Energy Firearm - if any.
As he was finishing his once-over of the rest of the gear he had brought with him: Hooks, Protable Grav-Repellors, Locator Beacons, etc. That Pionus finally made his Entrance. Clad exactly as he was at their prior meeting, the only difference being Leviathan across his back and a Helmet under the crook of one arm, he strode into the room followed by fifteen of his Sons Clad in Cataphractii Terminator Armor, each wielding a Volkite weapon and armed with a Blue-Bladed Power Sword he had never seen before. He noted that some toted Culverins and others Thunderhammers.
"They're my Depthstriders. They do this sort of thing as an initiation into their ranks so we're in good hands." exclaimed Pionus as he walked to his Brother, noticing the question in his eyes.
"Besides, it would not do well to have two Primarchs go into the depths of a Water World alone. Politics, Diplomacy, the Usual." He Shrugged. "Your Guard are welcome to joins us as well, if you want. I'd not deny you the choice."
"I would not deny them the experience, Brother" Daer'dd replied. "When do we depart?"
"Get into gear and we can leave immediately. We have a few hours journey ahead of us despite our close proximity."
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They were split up into groups of Three. Of the fifteen Depthstriders, Five were aboard each of the Phaetons. Of his ten Honor Guard, five were in each of the two back Phaetons with Pionus and Daer'dd in the Lead Craft. The interior of their craft was lit with a dim Red Light, the exterior an infinite inky blackness that, were it not for the sound of water moving across the hull, did not indicate movement, lacking the Stars Present in the void that one could use as reference points.
They all sat in Silence, having nothing left to talk about after their twelfth hour of travel. None were tired, a sense of anticipation slowly building among the Scions Hospitalier. It was at the eighteenth hour that the pilot messaged them that they were a few minuted from their destination. It was at this point that comms chatter resumed. As the Depthstriders made their preparations checking their gear and that of Daer'dd's Honor Guard aboard their respective ships, Pionus came over to him.
"Alright Brother, Stand up. We have to make sure our armor is properly sealed and tested. Wouldn't want to get crushed by the pressure or drown now would we?" He said, motioning.
Hunching himself over due to his size, Daer'dd got up and permit himself to go over the check by Pionus, in turn Returning favor.
Once done, Pionus asked "Sound off, Preparations Complete?" one by one confirmations rang across the tactical readout on their Helmets Heads Up Display.
Nodding, he continued "Roger that. Pilot, begin pressurization."
Immediately Daer'dd felt his armor strain a bit as the pressure was equalized with the exterior. A few minutes later he felt the vehicle slow down, come to a full stop and descend. Standing at the center point of the crafts floor, Pionus motioned for his brother to move to the side.
"Wouldn't want you to fall in as the hatch opens, Brother" he...joked? Daer'dd was caught a bit off guard, Astartes and Primarchs were not really prone to humor.
"Sergeant Aeus, you get the honor of first one down." As he spoke he pulled a lever on the wall and the floor hatch iris'd open. To Daer'dd surprise, the cabin did not flood, the equalized pressure keeping the water at bay. As he looked on, the Sergeant saluted both Primarchs and hopped in, a dull thud the only indication of him reaching the ocean floor, the light of the interior being unable to pierce more than two feet of the black, lightless water. One by one the rest of his squad dropped in each emitting their own thud upon landing.
Turning to Daer'dd, Pionus looked to him and stated "Mind the fall!" and hopped in, a noticeably deeper thud marking his arrival at the bottom.
Wasting no time, Daer'dd stepped in. He sank fast as something as heavy as he would be inclined to. The instant he was entirely submerged he felt his armor compress ever so slightly, the weight of the planets water pressing down on it.
The First thing he noticed was how ponderous his movements were in the medium. Next, was the all enveloping darkness and finally the deathly all-pervasive cold. Thankfully for all present, their augmented Vision permit them to see decently in the dark with limited light and their armor's life-support systems kept them reasonably isolated from the cold.
"Welcome to the lowest point on Iona surface, Brother" Spoke Pionus, his voice slightly distorted by the increased pressure.
"We are currently equipped with Twenty Hours worth of Oxygen, Thirty if we push it. The Phaetons will follow us at a distance of ten kilometers to make sure they dont get in the way of any Serpents we encounter."
"Take this time for you and your sons to get somewhat accustomed to movement out here" he said, popping out of the darkness to stand in front of his Brother, moving effortlessly.
For his part Daer'dd movements, while to a mortal were just as perfect, were slow and awkward unaccustomed as he was to the prospect of moving in Trillions of Tons of Water. His sons fared no better.
"Alright, since we haven't surveyed the area in a while, our maps and data of the trench might be outdated. We'll be moving along the right hand wall. Try to keep at most ten feet between any two of us here at any given time, if you see a cavern, mark the coordinates and inform us over the vox. To avoid any potential trouble, at no point in time is anyone to enter a Cavern, they're what Serpents usually inhabit. If you find a Cavern more than forty feet in diameter, again, mark it and call it out and drop a probe into it. If we're lucky we'll have a Serpent on our hand shortly afterwards." Stated Pionus as they started walking toward the aforementioned starting point.
"We'll be moving in a wedge formation, first position will rotate every half hour. Watch your step, we dont want anyone to fall into a Cavern, Whirlpool or other feature. If you do, activate your locator beacon and turn on your grav-repellor to stabilize and use your grappling hooks to try and get out. If it gets really bad we might be able to teleport you out but its no guarantee." He continued.
"If we meet any local Fauna, so long as they aren't aggressive, do not fight or kill. We don't want to chum the waters and bring out some of the more unsavory inhabitants of the Odyssian Trench. Additionally, be on the lookout for anything man-made. During the Dark Age, Iona had quite a few remote research centers strewn across the planet. We keep finding them from time to time, even now, and they usually contain valuable material." Moving to the head of the pack to start their march.
"Finally, if we find a Serpent, shoot it if you can. Your first Priority, however, is to hook and climb onto it, to get to the base of the skull and to deal a deathblow. Due to the speeds at which they swim and how far up they might go, the moment you feel your armor start to give, let go and fall off. A Phaeton will be able to pick you up." he said, shining his shoulder-mounted light into the first cavern they passed.
"In the extremely rare even that we find ourselves against multiple serpents, go after the larger one and let the Phaetons deal with the other unless your able to climb onto it." he concluded.
The following hours of their walk was spent in relative silence, call outs for caverns and breaks in the ground interrupting the silence. Every so often, they'd see Sharkoid Beasts swim into their cones of vision and quickly scamper away, other translucent fish would float in and out, carried by the currents. Other times eyeless fish would bump into them harmlessly. Periodically, at the outer limits of their vision, they'd see brief flashes of light; bio-luminescent hunters using self-produced light to hunt their prey.
On a single occasion were they attacked by a non-Serpent. While the combat didnt last long, the beast that attacked them was still formidable in size being a squid thirty feet in length. The Depthstrider who dealt the killing blow used his sword to carve out the beast prodigious beak as a trophy. And just as abruptly, they continued on their way.
It was at the end of the tenth hour with Pionus in the lead that he called for a stop. Slowly, he beckoned everyone close, to have everyone in sight.
"Sound off, how many have noticed our pursuer?" Of the Fifteen Depthstriders, seven confirmed.
"Thought so." he mused. "Alright. Heres the situation" He Started, addressing Daer'dd in particular. "For the past forty-five minutes I've been tracking a Particularly Large Beast that's been circling us, slowly closing in. I'm of the mind that its a Serpent seeing as we haven't had any signs of the larger fauna in the area and there seems to be a higher density of the smaller ones." He explained.
"Just be ready. In all likelihood its going to either charge at us from the front or back using the length of the trench to its advantage. I'm giving it an estimate of fifteen minutes before it attacks. Daer'dd, you take the lead. If anyone should get the honor of first blood and engagement, it is you, our guest. Worry not, we'll have you covered." He finished, patting his Brother on the Shoulder.
It wasn't long before Daer'dd's auto-senses started picking up their quarry. Over the course of the next five minutes, the whole party became aware of the Beast Hunting them, their suits now able to reliably track it at its current speed. At one occasion, he caught a glimpse of the beast through the all-pervasive blackness being warned of its sudden approach by the sheer displacement of water it caused. While he did not see it in its entirety, the fact remains that the little of its flank that he did see was twenty feet tall and covered in blood-red scales.
And just like that, it was gone.Though they would not wait long for Pionus called for a halt once again.
"Halt, we're no longer tracking it. Striders, into formation, it li-" He never finished his sentence, turning abruptly to face the darkness, Graviton Generators -- the biggest one on his back as well as smaller on his legs and arms -- across his armor, their sudden Green Glow signifying their activation, made the surrounding water hum.
As he Raised Leviathan to ready a strike and before anyone else could react, even Daer'dd, a Giant Fanged maw emerged from the blackness at lightning speed, colliding with Pionus Head on; a Grunt on the Vox Channel a confirmation. Almost immediately the Depthstriders Fired their Volkite Weapons into the sides of the beast, its head and Pionus long past, drawing their Swords to stick into its sides to anchor themselves to it. The only thing Daer'dd could think of doing was to grab on with his Gauntlets.
Immediately, he felt as if his arms would dislocate, so great was the acceleration but, he would not let go. Now fully on the Beast, he began to climb towards its head, water rushing past at speeds unobtainable by the biological. It made his ascent harder but not by much. The Real challenge was staying on as the Serpent Corkscrewed, climbed, dived, rolled, what-have-you. On his tactical read out he saw, besides himself and Pionus, astonishingly, three hundred feet ahead -- and he was far from the tail--, were six Depthstriders and Three of his own Honor Guard. And they were gaining on him.
Not one to be out done, Daer'dd redoubled his efforts climbing up the writing mass of muscle, scale and bone. Communication was all but impossible, their in-helmet microphones picking up only the sound of the rushing water. Foot by foot, he climbed, closer and closer did his tactical marker get to Pionus'. In the distance, he could hear the muffled roar of the Phaeton-Pattern Storm Eagles keeping pace with the Serpent.
While it wasn't necessarily tough or challenging to climb the beast, it took a long time. Fighting against the laws of physics was not something one could do without effort, after all. Still, after five minutes, he had sight of the head. As he neared he noticed that the mouth was locked open, the only indication of what was doing so being the butt of Leviathan sticking out of a Corner of the mouth and the Green Glow of Pionus' Grav Generators illuminating the interior of the mouth and surrounding water.
As Daer'dd neared the crest at the back of the Serpents skull, the beast took a dive, probably sensing the danger and wishing to rid itself of the unwanted passengers. Moving faster, he grabbed onto the crest, and pulled out one his axes and tried to hack into the area Pionus had Previously described. It was hard going, the scales being much harder than one would have thought and, due to the sheer size of the beast, he would also have to carve though hundreds of pounds of muscle before reaching the weak point.
Cutting through muscle and fighting for visibility through the blood darkened water, he continued. In doing so the Serpent became more frantic in its movements, more desperate to dislodge them. Far back he couldnt tell what was going on but looking at his tactical readout, fully half of the Astartes that had gotten on with the Primarchs were now reading as aboard the Phaetons.
Suddenly, his proximity alarms rang and he felt an impact on his back followed by violent scraping. The beast decided to run itself across a rocky wall - probably the Trench's, he thought. It then banked to the left and looking up slightly could see the ocean floor scant feet from him, still, he did not let go. His Tactical readout now showed only himself and Pionus on the Serpent. Before the beast could attempt another run at the trench wall, a sudden intense burst of green light made the whole beast suddenly shifted downwards and hit ocean floor decelerating so fast that it flipped on itself.
While the water did slow Daer'dd's fall, it did nothing to lessen the impact. Laying on his back at the bottom of the ocean he heard over the Vox channel:
"Get up Brother! I have pinned its head down! Quickly, finish it off as I hold it in place! Now Brother, My Grav Generators can be overloaded for only so long!" Pionus Shouted.
Wasting no time, he got up, albeit slower than he would've preferred. Directly in front of him he could see Pionus bathed in a Green Light, reflecting in all possible shades and hues off his opalescent plate, hunched over, one foot planted on the Underside of Leviathans Head pinning the Serpents Tongue, Lower Jaw and by extension, the whole Beast to the Ocean Floor, his back, left hand and armor holding back the upper jaw from crushing him.
Taking a Leaping start to climb back up the beasts flank to reach the top of its crested skull, Daer'dd had to fight being thrown off again as the Serpent writhed in a panic, its head pinned down by its assumed snack. Now on top of the beast and no longer having to contend with rushing water and gravity trying to throw him off he set to work digging down into Muscle, Artery, Cartilage and Bone. It was slower going than he wished but, once he had mad a large enough he set to just ripping his way through using his gauntlet'd hands.
Finally he reached it. The point on the Serpents skull where the bone was thinnest. Using his axe, he hacked into the skull removing chunks of bone as he went, exposing grey matter. Then, swapping to the Volkite Blaster Pionus asked him to bring, he put the muzzle directly in contact with the brain. In the split second before he fired, he whole beast convulsed and shuddered but he still pulled the trigger, his arm three feet deep into the back of the beasts neck. As the beast went through its final death throes, Daer'dd got off and went to the mouth to check on Pionus.
He found him, attempting to roll the Corpse over on its side, having probably taken the chance to stab into its skull with Leviathan when it convulsed. Levering it to rest on its side proved rather easy, the corpse being naturally buoyant. A few instants later, they were bathed in light as the three Phaetons arrived on scene and illuminated the area with their Searchlights, the embarked terminators descending to to meet their Gene-Sires.
Turning to Daer'dd, Pionus Exclaimed "You did it Brother! A Fine kill! This is the biggest specimen we've seen to date!"
Out of breath he replied "This is what you do for sport here? Seems unnecessarily perilous to go after such beasts."
"That we do. But, they're usually half the size of this Behemoth, it must be at least a few centuries old. Now, while we usually take a Trophy and leave the corpse to the Fauna, we'll be bringing this one back with us for research. But first" He said, walking back to the mouth "A Trophy to commemorate the moment. Sergeant, your sword." The Astartes in question walked over and handed the Primarch his Sword with which he proceeded to hack off a Fang.
Handing the sword back to the Sergeant, he picked up the man-sized fang and walked back to Daer'dd handing it to him "I believe this is yours."
The ride back was just as quiet with the sole exception of the Phaetons having to fly in a single file line due to the size of their cargo requiring all three to properly transport it. Their arrival back at Hive Alta was without fanfare but, once inside the docking bay and the Serpent on display seeing it undistorted by water or obscured by inky blackness did the impact of the did fully sink in. Fully Six Hundred Feet was its total length, its diameter 25 feet at its widest. Apart from the Orks Gargantuan Squiggoths, Daer'dd had never seen something so massive.
"A Beautiful speciment, isn't she?" Asked Pionus, walking up to stand beside him.
"Yes. Now I see why your legion chose red as its second color. But tell me, you said this was the largest specimen?"
"That we've found alive. Near old research centers we've often found Skulls of Serpents and other, potentially extinct species, roughly three times as large. Its honestly a Miracle we've somehow survived on the planet with giants like these roaming the waters." He replied, looking over the corpse of the Beast.
"Still" He Continued, "We're qui-"
"My Lord Primarch! Word has just arrived from the Emperor requests yours and the Legions Presence at the Segmentum Obscurus Mustering Point!" Exclaimed the Astartes clad is Shadow-Colored Armor.
"Is that so, First Captian?"
"Yes my Liege." Turning to Daer'dd, bowing before continuing "The communique did not make mention of the Iron Bears, Lord Primarch. As of now, the only information we've received is that we and the Drowned have had their presence specifically requested by writ of the Emperor."
"I see. Well, then. Sorry to cut the celebrations short, Brother but we mustn't keep the Emperor waiting. Captain Antonidas, send word to The Lady Inna that I wish to meet with her at her earliest convenience either at her Laboratory, Mine or the Hell's Heart. Also, send out a message to all currently unengaged Legion Assets to divert course to the Muster Point. Furthermore, have all Captains present on world and within two sub sectors to convene aboard the Hells Heart in Ninety-Six Hours time. Dismissed."
"Your will be done sire." he said, bowing to the Primarchs before him, turned on his heel and left the Docking Bay.
Turning to Daer'dd, "Looks like theres no rest for the Wicked. You'll have to excuse me yet again, I've matters to attend to. Please, stay for as long as you deem necessary and make yourself at home." He said, leaving his Brother.
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...Oh jeebus.
4000 Words and 7 Pages in a Document Writer 
Edited by Slipstreams, 20 August 2015 - 06:37 AM.