Space Sharks

This is what some believe the Space Sharks look like.

Space Sharks/Carcharadon Astra
Battle Cry	None (They are silent during battle, though if they weren't it should probably be "I'm a shark, I'm a shark, suck my dick, I'm a shark!")(Alternatively: [1]
Founding	Either 2nd (according to a GW article) or 6th (according to FFG)
Successors of	Either the Raven Guard, Night Lords or World Eaters
Successor Chapters	None
Chapter Master	Believed to be Tyberos the Red Wake
Primarch	Probably Corax, Konrad Curze or Angron
Homeworld	Fleet Based
Strength	1000 (ish)
Specialty	Operating out of the Imperium's Borders. Brutal close combat. Scorched earth policy.
Allegiance	Imperium
Colours	Grey, with black pauldrons and white helmet faces

This is what they really look like.

This is what happened when someone from Games Workshop watched Street Sharks and thought "there oughta be some spess mehrens like that." These guys call themselves Carcharadons" (Carcharadon, pronounced "car-care-uh-dawn" is the scientific name for a family of big sharks), or Carcharadon Astra if they are being extra formal, but everyone calls them by their low gothic name, the Space Sharks, because that is a fucking awesome name . They have light-grey skin and black eyes like sharks, and according to FFG they increase the resemblance by filing their teeth to be shark teeth. Their chapter logo is a white shark on its side and their colours are grey with black/dark grey shoulders. Once upon a time, they were light grey with a red stripe down the middle of their helmets and their logo was a stupid looking cartoon of a black shark with red eyes. Luckily, IA10 broomed that silliness under a rug and gave us what we have right now.

They're as mad as hell, even the Angry Marines might wanna think twice before cutting in front of them in line (perhaps this anger stems from their recruitment practices, see below). They're described as sneaking into place before going batshit insane with killer rage. But, their rage is always controlled and stuff. So they're like Khorne Berzerkers (though maybe the pre-Angron War Hounds are a better comparison) mixed with the SAS. They also like to cover their armour with Polynesian looking tattoos. Also they try to stay quiet in combat, because they think it makes them cool sharks can't talk. Their specialty seems to be committing indiscriminate genocide, sparing only children they can enslave into being Chapter serfs or turn into more Carcharadons (said children have to fight each other to the death). They also like to wear Heresy-era armour to give people more incentive to buy from Forge World.

The Carcharadons come up in the Badab War, where it's kinda hinted that they're Raven Guard mutants or descended from those other deranged genocidal space marines- the Night Lords. Anywho, they're deployed to Afghanistan in space to fight the space Taliban and they solve the problem that the Fire Angels had been having by killing everybody to root out teh terrorists. Grimdark. Then they go over to Badab and blow the place up, ending the Badab War. Then they go back to the ashes of space Afghanistan and make a bunch of boys kill each other to become the next generation of Carcharadons before heading back out to smash someone else's planet. Also, according to rumor, they helped to trash Failbaddon's 7th Black Crusade.

Their leader is Tyberos the Red Wake, a terminator who couldn't decide if he liked lightning claws or chainfists better, so he made Lightning Chainclaws...IN SPAAAAAACE! He can rape just about anything in the game in close combat. His Scent of Blood rule makes him and and any Carcharodon unit subject to Rage +1 strength for the rest of the game. He is reasonable enough to wear helmet and do not carry banner and shitton of flashy trinkets on his armour, unlike most other chapter masters, whose wargear just screams "Shoot me down, sniper!" Also, allows you to take a unit of lightning claw equipped assault terminators as troops; and he and any unit he joins have preferred enemy (infantry). Why aren't you taking him again? He's never explicitly said to be Chapter Master, but its a forgone conclusion since he's got the same stats as one.

Not as cool as the Saharduin, who are actually sharks from space. They do, however, share the same battle cry.

Their beakies look fucking amazing.

Organization

The sharks are assumed to be a fleet based chapter. They follow the battle half of the codex but ignore everything else about organization. Cruising around in the void between beyond the galaxies edge can be nasty business. Years without resupply or any kind of constant reliable resource means they must be resourceful. Because of this each company practices high self-reliance, salvaging, repairing and re-purposing stuff to make sure it lasts as long as possible. This is why they support so much working heresy era stuff. They also don't use reserve companies(realizing that having 100 of the finest warriors sitting around doing nothing is fucking stupid). Each company is thought to be a self contained force, with their own scouts, and veterans, ensuring they've got guys for every situation on hand. This has drawbacks of course as they can't simply ask for reinforcements from a reserve company and must make do. At the same time it means that they've got all their companies actively doing stuff.

It could be theorized that part of the scorched earth campaign the chapter did during the Badab War was in fact them violently restocking their inventory after having spent so long outside known space. Filling up on ammo, weapons, supplies, and grabbing anything and everything that could be useful, before they inevitably returned there. We do know that they claimed a bunch of recruits post-Badab, and they probably do this after all their big campaigns (maybe every time they come back into contact with the Imperium).

Loyalist Night Lords

Fluff-wise, they are "suspected" confirmed to be of the Raven Guard in the Horus heresy Book 3: Extermination. While they do share the Raven Guard's love for low-profile sneak attacks, the Space Sharks are excessively brutal in their missions. This contrasts with the Raven Guard's usual clean and efficient MO and somehow falls more in line with the terror tactics used by the Night Lords. Alternatively, there are bit more facts that point to them being such, like:

• Old as fuck and of no known founding. In fact if the Imperium's shoddy record keeping can be believed, they were recorded active as early as M32, just 100 years after the Horus Heresy. Further cementing the fact that they must have directly descended from a legion.
• Incredibly reclusive.
• Pale with black within black within black eyes. This was a common trait of people living in Nostramo the prison moon of Lycaues, who were kept in the perpetual night time dark mines, cells, and tunnels.
  • While this is also caused by the gene seed defect of the Raven Guard, the Space Shark's gene seed were unusually pure, meaning that their features were hereditary.
• UnusuallyCompletely normal violent combat style for a Raven Guard descendant that's afflicted with the Sable Brand, AKA Ash Blindness that is the "defect" of the XIX geneseed since the Emperor founded the XIX. Their leader Tyberos and his Terminator bodyguards, for example, cut a bloody path through the secessionist in the Badab war by literally murdering every enemy in their way like a bunch of angry Khornate Berzerkers or Sable Blind legionaries.
• Regular use of brutal terror tactics. Some examples include:
  • Bloodying worlds loyal to the Mantis Warriors in the Endymion Cluster during the Badab War in order to force them into a fight, which the Mantis Warriors obliged. The result was the Mantis Warriors being so screwed over by them that they were unable to further participate in the Badab War
  • Caused the power reactors in Badab Prime's hive to overload, causing a tectonic event that more-or-less fucked over the entire planet. Whole-sale wiping out most of the rebel forces and 600 members of the Star Phantoms, their allies who were on planet during the fighting. The Star Phantoms were not amused and are still pissy about the Sharks for that incident.
  • Went to the Tranquility system where a number of Mantis Warriors fortresses were located. They raided and pillaged them all for supplies and took all the men in the system eligible for Space Marine augmentation in order to replace their losses in the Badab War. That didn't stop there because then then forced all those people to fight to their deaths and only those who survived were deemed worthy to be inducted into their ranks.
• Lots of heresy-era goodies. Something newer chapters were unlikely to have in large numbers, or at all.
  • Most of their standard armors are the old MK.V "Heresy-era" armor and their Terminator armors were noticeably old, although kept heavily modified and upgraded to keep them combat-capable.
  • Most of their weapons were heresy-era weapons.
  • Their Battle Barge: "The Nicor" is a Charybdis-class cruiser, used by the Imperium during the Horus Heresy.
• Tyberos' custom lightning claws, Slake and Thirst, resemble the claws Curze Corax used.
  • They are also relic weapons that even Mars has no record of ever producing.
• Suddenly appear, rush the enemy, rip and tear, and disappear.
• Basically, they fight like a more 'evil' version of the Raven Guard, see the Heresy-Era Pale Nomads chapter of the XIX who, literally, have the Carcharodons paint scheme and the same tactics. The super formality and relic tech means they very well could have been in operation since the heresy and the fact the 7th Predation Fleet of the XIX Legion that they patrol the edges of Imperial space means that there'd not be much of a chance for their cover to be blown.
• Think about what you'd do with a bunch of loyalist Night Lords left over after the heresy. If you send them out to the edges, you don't have to deal with their creepy ass batmaness and if they turn on you due to crazy gene seed juju, they're not going to wreck your day. Equally, since they've proven their loyalty, their brutal stealth tactics are perfect for disrupting potential enemies behind enemy lines and this is exactly what Charchadons Astra do.
• Sharks are nocturnal apex predators. i.e. "Night Lords" Really, read HH Book 3. They're what was left of the Terran Pale Nomads Chapter assigned to the 7th Predation fleet during the Heresy.

The following is old, before the release of HHB3 Extermination:

For all these similarities, however, the Raven Guard theory has some significant somewhat concrete evidence for it.

• The "Raven Guard" theory comes from Death Watch apothecaries analyzing the gene-seed of fallen Carcharodons. Apparently the Raven Guard gene-seed has several distinct traits to it that don't show up in other Space Marine gene-seed, and the Carchardons' gene-seed also has these traits. In other words, the whole "Carcharodons are probably Raven Guard successors" thing isn't something the Imperium just pulled out of their ass or theorized from the Carcharodons' fighting style. There's actual significant DNA evidence to support it (although the evidence is not completely 100% certain, which is why they are officially only "suspected" of being Raven Guard successors)

• In the newest HH book: Extermination, it is hinted stated that the Raven Guard used similar berserk tactics to the Carchies during the Isstvaan fuckup. Tyberos's helmet can also be seen in the book, and the survivors of the 7th Battalion wore dark grey suits of armor and were sent into the "outer darkness", just like the Carcharodons. It's pretty clear FW and Will Hayes intended HH3:Extermination to be a clear nod to the Carcharodons being the remains of the RG legion's 7th Bn.
• The founder is probably Shade Lord Arkhas Fal, once the Master of the XIX Legion. When Corax took over the Raven Guard he tried to purge the more cold-blooded ways of the Terran Xeric tribes which had once defined the Legion culture. Several of the Legion's highest ranking officers were displaced or reassigned to non-command roles, including Arkhas. A small number of mostly Terrans of the Legion of old, had been assigned to many posts beyond the fringes of the Imperium, some in independent nomad fleets, other attached to various Rogue Traders Militum. One of these fleets was commanded by Arkhas Fal on the direct order of the Primarch when Corax took over the Raven Guard. What became of the Shade Lord, his fleet and the other elements may never be known, and the fact that Corax appears to have made no effort to recall them suggests they were considered a body apart from the bulk of the Legion. Sounds familiar?

• Yet another possibility may be World Eaters, since Space Sharks are silent and brooding outside of battle but go absolutely batshit crazy when in battle, no questions asked and they seem to have a preference for Power Axes, which is somewhat unusual among Space Marines. It's even seen that way in the Deathwatch RPG.

On the Tabletop

Carchadons Chapter tactics gives all Space Marines models Fear, and allows Tactical marines to replace their bolters with a chainsword or keep it and buy an additional close combat weapon for 1pt each. In addition they gain Rage after destroying or forcing an infantry unit to fallback in close combat, however they must consolidate towards the nearest unit they can hurt (after all, the rape train has no brakes!). You can only ally with Imperial Forces and all of those are bumped down to Desperate Allies. All this means that, with them, you play Horus Heresy World Eaters with Fear and all the shiny new toys of the 40k arsenal of Space Marines.