Working on an idea for a plotline and need an atrocity that would be comitted by nice upstanding boyscout-smurf ultramarines that are honorably doing their duty. (Not fallen marines or any sort of chaos plot, just good old fashioned Imperialistic horror).

Trying to come up with ideas that fit both the setting and the perpatrators, which will be sufficiently horrifying to make my players go: "but..but..I thought they were the good guys...."

Any suggestions?

What about a battlegroup sent along with other Imperial forces to investigate a suspected tyranid incursion on a world with lots of Imperial civilians (or better yet, a world with a very large Schola filled with orphaned children), of course this world has been somewhat infiltrated by tyranid genestealers, but some old, ancienc decree written at Macragge after the tyrannic wars demands that any Ultramarine, no matter where he may be located is honorbound to exterminate anyone or anything having even the most remote contact with an organism of tyranid origin. Meaning of course that the SMurfs in this scenario will go to town, butchering a bunch of orphaned children.

Sound atrocious enough for ya?

Varnias...thats the most demented thing ive ever heard...good job man

another idea might be that in the heat of a small battle say a 100 guardsman and your acolytes (they were conscripted or just thrown in) and the Ultramarines were ordered to slay the guardsman but spare your acolytes by orders from the inquisition (they are fighting things the guard isnt allowed to know about so they have to be killed) the marines will slay good emperor fearing men but spare your acolytes in the midst of the bloodbath hehehe.

A small squad of the marines are parading through a densely populated area. Perhaps they are showing off, acting as an honor guard, or transporting something or someone of importance. Suddenly, the enemy strikes from cover. Panic grips the thronging masses who have turned out to see these mythic figures and, due to the attack, the Smurfs objective and mission is in danger. Perhaps they need a clear line of sight and fire to engage the enemy so they begin clearing civilians (men, women, and children) from the newly created battlefield... with bolters and grenades. Perhaps the sargent is felled by the first shot in the salvo from the snipper and the apothecary has to chop, hack, and blow his way through the panicked throng (and little Suixie as well) to get to him and dose so without hesitation. Perhaps the attack is endangering that which they escort and the marines need to group together to defend it, but they're separated by the now panicked masses -queue the hack and slash with some battle field clearing afterwards with Imperial men, elders, pregnant women, small children, any and all of them being cut down without discrimination). And of course, it's all done in a cold and calculating manner in accordance with standard tactical procedures.

Graver said:

I like this, but I think it needs an extra dose of totalitarian evil. So UM escorting August Personage, parade, and so on as above.

But instead of an attack, they encounter a group of non-violent but loud and shouting folks who have broken out of the crowd and into the parade route trying to speak to the person the UM are guarding. (A greviance, a request for a blessing, who knows just something shouted at the top of the lungs with lots of arm-waving)

Spokeman for group says wrong thing, making marine view him as heretic/threat, he takes bolter shell to face. Stunned silence, dead guy's comrades panic, one reaches to pull something out of his robe, someone shouts "GUN", Marines open up, mercilessly pursuing the now fleeing into crowd "heretics", mowing down civilians to protect their principal and so on as outlined above.

In the aftermath, guy with "gun" turns out to have been pulling out something innocuous like a dataslate or pict recorder.

Thoughts?

DocIII said:

The thing is, in the grimdark, darkgrim "the-ends-always-justify-the-means", far future of the year 40.000, many things aren't generally considered very "atrocious" due to the state of things in the Imperium of Man.

Which is why I suggested the butchering of orphaned children, since the idea would probably make even the must puritanical Inquisitor a bit reluctant. First of all, the victims are children, second they are orphans. Sure, it's a bit extreme, but it's pretty hard not to sympathize with the victims in such a scenario, even in the darkgrim, grimdarky darky Imperium of Man.

EDIT: However, one thing you could do is a scenario about an Astartes cover-up. Where one particular legend claims that several (still living) Ultramarines saved many people during a dangerous situation, but the truth of it all was that these innocent people died at the hands of the same Marines, but all remembrancers and correspondents were instructed by the SMurfs themselves to repress the truth and officially claim that these atrocious marines were saviors rather than butchers.

Toss in an Inquisitor or two, along with his/her acolytes among the victims in this scenario and the Ordos would have good reason to investigate the affair.

DocIII said:

To be honest, there's an easy one that springs to mind - it doesn't really have to be an atrocity by the standards of 40k (which is a difficult bar to reach, really), just an adequate demonstration of just how terrifying and merciless the Astartes truly are.

For whatever reason - perhaps a natural disaster, perhaps an invasion... could be anything, really - large groups of people are being evacuated from a heavily populated area. All those deemed to be worthwhile have been taken away already, and the transports are full as they prepare to depart for somewhere safer.

The Ultramarines are overseeing this retreat for whatever reason. It needs only be a squad or two. Every marine is wearing his helm - the tendancy of the art and models to show leaders without helms is often to humanise and make identifiable the Astartes as human in concept, which is contrary to the point here - and they're communicating entirely on their squad vox networks, so they don't speak to anyone who isn't on that line of communication.

A riot begins, as the crowd pushes for the remaining transports, and the Astartes quell the riot in the best way they know how - precision bolter fire scything through the defenceless civilians. To an external observer, they just open fire - there's no discussion, no orders given, no communication of any sort. They don't miss, they don't hesitate, and they seem capable of spotting and dealing with things (like retaliating civilians throwing firebombs) with inhuman prescience (as their autosenses help pick out targets sooner).

The best way, IMO, to make the Astartes scary and demonstrate that they're really not nice people is to dehumanise them as much as possible. They're faceless, identical, unstoppable, remorseless and entirely without mercy. When not fighting, they remain perfectly still, resting their bodies within the rigid shell, and appear to be statues at first glance. When they do speak externally, it's distorted by the loud hailers in their helms, a harsh and booming tone that could come from no human throat, but the rest of the time they're apparently silent, all their speech shared only with their brethren via a local vox system. More importantly, there's no moderation in their method - they don't shoot to injure or incapacitate, and they don't allow surrender - every target is killed in the most expedient and unpleasant manner possible, because that's what the Astartes are for - their wars are terrible, gore-soaked things that normal people should never have to see. The Astartes are not heroes, they are weapons; they are not glorious, they are wrath incarnate.

Three cases of mistaken identity come to me:

1. The Acolytes are sent to a feudal planet to inspect an old church, a few millenia old. Once they get there they see a cute little village, who uses the left-overs of a Black Templar mission as a church and worshipping ground. The people are rather devotet to them, and fashioned a reliquae out of the bones of one sceleton found in a open tomb. After a few days of investigation the PCs decide to leave the nice, but worthless, village alone and get back to more serious business. Just as it has to happen one of the many strike forces of the BTs shows up in orbit. They look for the same church ... and their commander nearly gets a heart attack at both hearts as he sees the violation of the sacred bones of one of his brothers. So he orders his battlebrothers to reclaim the bones and the chapple from those defilers, with all the wrath only a SMurf can bring to bear.

2. Similar to number 1: some fifty years ago there was a small Genestealer-problem on a backwater planet. A team of Ultras was sent to deal with the situation since they had the necessary experience. Due to a little warp-malfunction they come said 50 something years too late, the PDF had been able to take care of the problem themselves. Now, the SMurfs don't ask 'what's the time', they lock up and land, shooting and burning every even possibly infected person, just as they had been ordered.

3. A Fallen Angel (a Dark Angel brother who .. ah, i'll explain it later somewhere else) is hiding on a distant planet, trying to forget his sins against the Emperor and his brothers. Since he' still a 7-8 foot tall giant after a few decades he became the hero of the nearby villages, and later even mayor (he's got the brains, guts, muscles and knowledge). He cares for his little villagers, protects them and otherwise lives a quiet live, trying to repay his failures by watching after them. Your PCs are in the area, looking for the giant-mayor who is too strong and too old for a normal human being. But they are not the only ones. A Ravenwing-squad is on the planet too to take the traitor home for interrogation. No matter what the Acolytes do, the simple villagers love their just and noble mayor, and surely wont let him be taken away simply because he made a mistake in his past, while the Dark Angels will do anything (yes, anything) to capture him.

Varnias Tybalt said:

This could easily be expanded to a whole adventure.

The genestealers have not yet felt the presence of a hive fleet, so they are laying low, trying to infiltrate as much of the planet/population as possible without blowing their cover.

They have infiltrated the school and now all the teachers are 3rd generation hybrids. So far they haven't harmed the children to avoid discovery during the annual medical checks performed by government doctors.

This works even better if the school is a normal school. The 'stealers' will have extended their psychic influence to the parents of the childen, creating a large body of expendable psychic slaves ready to riot.

The school basement has been expanded to include a network of caves/tunnels where the broodlord lives in the center of his invisible web, like a big fat, dangerous, psychic, alien spider.

The tunnels can also have 1st and 2nd generation hybrids with extra genestealer arm, carapace etc., full genestealers, lictors, breeding chambers where infected humans are kept and anything else the GM can come up with. Lots of reasons for fear checks and insanity points.

The adventure has 4 parts:

1) investigation to determine the extent of the infestation. I guess a psyker character comes in handy here.

2) Investigation/infiltration og the school. Find clues to the fact that the children are ok.

3) Descent into the tunnels. Lots of aliens style tunnel creepiness. When the characters enter the tunnels, the genestealers know their cover is blown and they "activate" the parents, starting a riot outside.

4) As they emerge from the tunnels, the characters has to make their way back to base while escorting a group of children while the rest of the task force quell the riot with bolters and flamers, massacreing their parents én masse ( more sanity checks ? ).

Since no one else in the task force knows abuot the children, the pc's may have to fend of/flee from a few squads of over-zealous space marines. Allowing a couple of children to be blown away would ram the horror of the situation home and could be reason for a few Fear tests.

Back at base they have to convice the guards to open the gates, allowing possible infected persons inside.

Finally they have better make a full report to the task force commander :-).

Lindgaard

The posibility of any member of the population being infected would act as potential justification for the action in any genestealer based story and as such interfere with the impact I'm going for.

While I love a good genestealer cult infestation story as much as the next guy (they do make great adventures), won't work for what I'm going for here regardless of the direct identity of the victims (unless there was zero chance they were infected and they were killed anyway)

DocIII said:

Well that's why you let the acolytes being the ones investigating the infestation in question. Let them find evidence that there actually was zero chance for the population to be infected (or better yet, complete evidence that the infestation has been wiped out decades ago) but that the SMurfs simply wouldn't listen to that and instead going for an unecessarily paranoid "better safe than sorry" approach.

After all, the Ultramarines are the most inflexible protocol knights there are, and if their standard procedure say: "Burn! Cleanse! Kill!" for the situation at hand, it wouldn't matter what sort of evidence the acolytes of an Inquisitor uncover.

segara82 said:

While great story ideas, all three of these take the control of the story out of the PCs hands and for the most part the GM will be telling a story for his PCs, not with them.

Try giving the PC's a level of control. Have their Inquisitor assign a squad of deathwatch, or even an allied squad of ultramarines, to join them for the purging of a known cult, with the acolytes arch nemesis at the head of it. Over the course of a month, the acolytes and the marines should get to know one another, have the marines swear oaths of loyalty and protection to the acolytes, and make them seem like heros of the imperium. Then, one on planetside, let the PCs do the investigative work to find the RUMORED location of the cult. Upon reaching the location you find a bustleing trade market, and your PC's will be thinking "How are we going to find a cult in here?" while the marines are thinking "Alot of people in this cult, I hope I have enough rounds"

The complete annihlation of the marketplace, women, children, old people, people begging for mercy, people praying to the god emperor for salvation. All of them die. Then if the group is clever they will atleast look into finding the remains of the cult, and they will find 5 robed bodies, but not neerly enough for them to be the entire cult, and the arch heretic's body is not amongst the dead. They had gotten away in the marines carnage. This will teach the acolytes that sheer brute force is not always the best way. So you show how horrable the astartes can be, and teach your PC's a valuable lesson in investigation.

Another "atrocity":

Imagine a world at war. Perhaps orcs invaded perhaps civil uprising. But it has become that bad that small numbers of UM have been called in.

What ever the enemy is, they have been excellent at destroying food supply convoys (perhaps Traitors from the PDF/IG ?). Since new food stuff is need real bad for the front line, it will be guarded by a squad of UM and a Razorback. Since rations are needed QUICKLY, they group start literally PILLAGING the countryside. Taking away all the food from the villages. Those that resist are shot on the spot.

I like the sort of atrocities that depends a lot upon your view of things. Most of the information that the inquisition handles is shared on a need to know basis, and the acolytes don't need to know everything.

A squad of marines can for example be sent to take out a noble family that is believed to be supporting a planetary governor that seems to be plotting to rebel against the imperium. This would be a precision strike with a squad or two of marines deploying by gunship, breaking in, killing a few hundred people from the traitors family and employees. Preferrably all of his family since you don't want any future heroes hiding under a bed witnessing their mothers death at the hand of the corpse emperors merciless lackeys, it is practically guaranteed to turn into a far too cheesy story. Then the marines move out again. Do the marine incursion during a time when the acolytes are visiting said noble, maybe using hooks from "rejoice for though art true" if you have played that. Have the marines be from one of the less commonly depicted chapters with a strange name and dubious iconography, like the Flesh Tearers (who btw actually likes to eat the flesh of their enemies to aquire their skills and knowledge, and are blessed with this ability by the Emperor). The acolytes will probably scream bloody murder and, unless they make a skillcheck for the pretty rare skill Heraldry, chaos incursion. Hilarity ensues when one-hand-does-not-know-what-the-other-does takes full effect.

Alternatively and on a much more personal plane: There are ways to indicate the different perspectives between a human and a brainwashed superweapon. Dehumanize them like Noonehere (sorry about the lack of leetspeech in my spelling) suggested. Show that their priorities are very different from the PCs.

Have a squad of marines deployed under the acolytes nominal command to aid with retrieving important personel from a recently rebelled city. In the middle of the chaos, while locked down in an old warehouse and under fire from traitor guards a dropship suddenly burst from the sky, the squad embarks and takes of, leaving acolytes and civilians. If prompted the sergeant quotes a textbook telling the acolytes that they are under no obligation or even liberty to discuss or relay orders recieved. If the acolytes tries to discuss the matter or even get in the way one of them might be shot for obstructing the emperors finest. End with the sergeant standing on the closing ramp and halting takeoff with a raised hand. He removes his helmet. His face, lined by 300 years of the most horrid combat experience softens into a nearly human expression of remorse as he offer to break protocol, delay following his orders and extend aid to the acolytes... by firestorm bombing the entire sector they are holding out in. Thus making sure this key personel does not fall into enemy hands and that the acolytes will be spared the risk of betraying the Emperor (blessed is his holy wrath, delivierd through this boltgun) by succumbing to interrogation and torture after an eventual capture. When the acolytes refuse this grand offer; look personally offended and like you knew there was nothing to be gained by trying to bend protocol and that you will certainly never attempt to do so again.

Later when the acolytes return, badly shot up. Critizise them for having lost some of the personel they were tasked to escort. They might query their inquisitor on what was important enough to justify leaving them high and dry in the middle of enemy territory. Just deny them any information at all on the matter. Preferrably refuse to even acknowledge there ever were a squad of marines assigned to them, let alone in the system at all. "I will neither deny nor confirm the suggestions that I would have knowledge about or influence over Adeptus Astartes activites in this sector."

I think it's very difficult to come up with a good story about SM atrocities. All the examples above, even my own, are just examples of Space marines doing their job. In some of the stories they are doing a bad job because of old or incomplete info, but they are still doing their job.

The Space marines only fight in the more dire circumstances, in the most important battles, and that may require heavy handed methods.

Space marines are made to save humanity, not nessecarily save humans.

Don't forget that the inquisition has no problems wiping out entire planets or killing a whole guard regiment if there is suspicion of chaos taint on the principle "better safe than sorry".

Lindgaard said:

Exactly, which is why I believe the GM should make it appear that the SMurfs or perhaps an Inquisitor is doing such atrocities on a blatantly arbitrary basis.

Yes Inquisitors call down Exterminatus on some worlds, but no Inquisitor would do it lightly or arbitrary. In fact in the eyes of pretty much all sane Inquisitors exterminatus is a "last resort", only used when the Inquisition has failed to do it's job properly. Not only do the countless deaths of innocents count to this fact, but the fact that you're basically destroying an entire world in order to deny it falling into enemy hands. An entire world is an invaluable resource to the Imperium of Man, and destroying it will have severe consequences to an entire sector's economy. Not to mention the potential aftershock of destroying a world that is quite known throughout the sector (protest riots, seeding anti-Imperial thinking etc.)

The same goes for Space Marines. You can only blame that you're "just doing your job" for so long. The trick for the GM here is to make a distinction, where the actions of these marines might be justifiable on paper will seem horribly arbitrary, unecessary and pointless in real life. The fact that the Player Characters are agents of the Inquisition should make this task a lot easier, since you can construct the scenario in such a way that the PC's are privy to important facts proving just how unecessary, arbitrary and pointless the SMurfs actions are. Like wiping out large portions of students on a Schola Progenium world, merely because they are honorbound to do so, and not because the children would actually pose a real threat.

To add even more insult to the injury, the PC's could be allowed to present proof of this to the acting Space Marine commander, showing some gross misconduct carried out by his men, only to see the dataslates and documents being torn to pieces right in front of their eyes. Effectively covering up the entire incident.

This could serve as an explaination to why the Ultramarines in particular have such good reputation. It's not because they are "the elite of the elite" or "living heroes" or any other such bull. But because their commanders have learned the importance of good public relations. So they cover up all actions of their men which could be perceived as cruel or evil in the eyes of normal humans. Mercilessly opening the eyes of the acolytes investigating the affair that all those paintings and statues rasied of Ultramarines, and all the legends of bravery and goodness surrounding them are false PR-stunts and nothing more.

Varnias Tybalt said:

he he . . brilliant !

Lindgaard said:

Yeah, I have my moments.

Suffice to say that most of my scenarios include some form of lies, deceit, treachery, depravity and/or betrayal. I try to strive towards putting the "Dark" in GrimDark.

Though I must admit that I've run into a snag. I want to participate in the Dark Heresy Adventure Contest 2009, but im having a severe case of writers cramp. I hate the fact that I can conjure up pretty cool extrapolations on ideas by other people, but sometimes get completely stuck when trying to come up with an original concept of my own.

Hi:

For any atrocity just check the (real) news about any war/conflict. You also could go back to the Crusades, esp. the sack of Constantinople. Sadly, pretty standard stuff in Human history.

L

i'm going soft in my old age. i swear it. i will be the voice of dissent here.. i'm usually all for the darkness and shaking up the Imperium. but sullying the Ultramarines is just...wrong.lol. i was a proponent on another post that was all for someone destroying the Astronomicon.

there are few things in the Imperium which are good and honest. personally and i can't think of one..except the Ultramarines and the poor faceless masses of human beings. to destroy what they represent. what Maccrage represents. that sense of duty. honour. principle. compassion. and truth. it seems...just damned wrong. and i don't even LIKE the Ultramarines. i'm a Blood Angels man.

if your campaigns are so grim and dark with no real light of the better part of humanity. just what are the Acolytes fighting to save?

still for the purposes of your adventures. some good atrocities here. have at it. the only question I raise..is how will it end?

levelling a charge at a Chapter is no small thing. it will be disastrous. a good chance the Acolytes will not survive and risks the Imperium being torn in two. going after the Ultramarines is especially dicey. they are even more proud than most Chapters. other Chapters will ask the question potentially 'if they can go after them, they can come after US'. at least a few Legions will join particularly those that the Ultramarines gave rise to..the Sons of Guillaume, etc.. also they will have to fight and defeat the Maccrage system.

still have at it...played right it can shake the foundations of the Imperium itself.

the liegekiller said:

I dunno... it always struck me, and this is a notion reinforced by the new Space Wolves codex, that the Sons of Russ were far more the 'honest hero' types than the Ultramarines (Logan Grimnar's outrage at the Inquisition having the population of Armageddon sterilised and replaced after the 1st War for Armageddon being the finest example of this). While the Ultramarines are extremely dutiful and honourable... which is the greater duty? To safeguard a dozen men, or to safeguard a million? Which will see honour shaken more severely? The death of men or the death of worlds?

Of the First Founding Chapters especially, any of them can easily be painted as good and noble and honourable heroes... well, maybe not the Dark Angels, but they've got serious PR issues... but it's something the Horus Heresy novels depicted quite well, IMO. The Astartes can be seen as towering heroic, almost godlike figures to those mortals that see them, but the way the Astartes are built to fight, the way they're trained to bring death, means that they seem far less heroic if you actually see them in battle - they become a terrible force, wrath wrapped in flesh and steel. As noble as they might see themselves, as just and honourable as they may act... when the time comes to take up arms and fight, the Astartes should always be utterly terrifying to witness, whatever heraldry they wear or genetic legacy they claim.

N0-1_H3r3

yes the Astartes are terrible to witness in battle and they should be. i have spent 14 years in uniform and 6 as a private contractor working abroad in Iraq, Afghanistan and a number of other places. ppl in the combat trades are trained to the dirty things which most others turn away from . but when the time comes to do what you must battle turns brutal and ugly and chaotic. my point is what they do is terrible but that doesn't mean that they are lacking in morals and are savages. the ppl that see what you have done care for their lives and loved ones and their way of life. they may not see you a a hero but they're all **** happy to be alive because of your intervention. and they'll hug you and kiss you just the same

lets not forget that even described within the chapter histories one can see certain dark traits. the Ultramarines have remained apart from this. there are plenty of other chapters that have stained records. pertaining to what you cite from the new Space Wolves codex, their outrage is outrage, they did nothing to stop it nonetheless. the ultramarines would have also done nothing to stop it. unfortunately its tough to cite an example as this as emonstrating the honour and truth over one chapter over another. there really isn't enough known about full chapter histories to form a record. and in the rather pointless to my mind. we can only work from the basis of what we know of the chapters.

i DO think the space wolves are an honourable chapter. however numerous references have been used to them being under suspicion for lacking in genetic purity, their gene seed corrupted. the Blood Angels is another. my point is the Ultramarines are to many in the Imperium..that very bright shining star of hope. and that is how they are depicted within 40k lore. they may be terrifying to witness as all war is whether they may be SM or the brute force of the IG.

but the Ultramarines...guilty of atrocity? sure its possible....grumble grumble...

i'd still rather see the Astronomican burn...

the liegekiller said:

And that's all entirely reasonable and beyond dispute... when we're talking about humans.

How can someone be compassionate about the lives of normal men and women when they've not lived the same kind of life? For the Astartes, their normal human lives end in their early teens and are on the other side of years of excruciating surgery, intensive hypno-indoctrination, and brutal training. Morals are imparted by upbringing, and for the Astartes - any Astartes - the part of their lives which would give them anything resembling normal human attitudes towards things is a very small and very distant element of them, before you even consider the nature of human morals in the 41st Millennium (which, amongst other things, condone genocide on a massive scale against things that don't fall into a particular definition of 'human').

The Astartes, IMO, don't really understand normal humans any more. They're so distanced and so far removed from what it is to be an ordinary human living an ordinary life that they can't truly comprehend it. And, more importantly, it isn't their concern - loyalty to their superiors and to the Emperor, mastery of the arts of warfare, honouring those who came before you to stand and face the worst the galaxy can throw at mankind... those matter.

I tend to view it that one of the defining traits of the Imperium is that those who must face the most terrible of foes do so to protect the innocent masses of mankind, but that in doing so, those same defenders of mankind must separate themselves from that mass. The Astartes sacrifice their humanity to stand firm against impossible odds and unimaginable horrors. Those who serve the Inquisition must sacrifice innocence, sanity, the comfort of ignorance and the safety of what might ordinarily be considered 'right' and 'just' in order to protect those who can still cling to those things - Inquisitors in particular are given the awesome responsibility of being able to choose which worlds live and which ones die, and for them, normal human notions of right and wrong are stretched to breaking point. Murder a man to save a world? Murder a world to save a sector?

For such beings, to protect mankind so that they can continue living their lives in some semblance of peace is the ideal... but the means they use are ones we may see as being abominable, utterly atrocious and beyond redemption. That is, IMO, the point. That the few must **** themselves, must be monsters, to fight that which is worse...

you used the word 'human' quite a bit. without getting into a huge long debate on this. one has to ask what that really means in this context. i cannot dispute what you say about the Astartes, you are correct that there is something that separates them from the masses. there are a few somethings. their size, genetic reengineering, psycho conditioning and grueling training structure make them so. the society they are raised and steeped in reinforce these.

i do not think they understand humans at all..they have no chance to as secluded as they are. they are cut off from society and granted a divinely given right to cleanse and purge. that said because they cannot understand humans..does that make them not human? human beings can't understand human beings within a culture. it gets even tougher to understand outside of a culture or religion. but these marines experience the same kinds of emotions as the rest of us..fear, rage, mercy, love, compassion..at least all the literature has described a variety of very human traits. so this beggars the question. what does it mean for an Astartes to be human if not that? if not demonstarting these traits. is a murdering rampaging Astartes different from a murdering rampaging hive ganger?

sure in the technical aspect of potential body count, but in the intangible terms of defining humanity? i don't think so. also humanity in 40K sees, understands and realizes their divine right to bring bolter and fire to their enemies. they are romanticised and seen of in awe by the masses. this has been discussed also within 40K. also discussed has been the recognition by the Astartes to act as the protectors of man and all his domains. you are familiar with 40K, i know from your writings. these Astartes were raised from as human children within human societies with human families and friends. they were not vat grown. even the Astartes way of life is altogether very human. real cultures have been raised with a warrior ethos. in 40K there are numerous examples of this. the Cadians come to mind. most ppl living in this kind of society would find other ones altogether very strange.

their understanding of humans is not necessary on any level. they don't even understand themselves. the job of Marines is to quite simply destroy the enemies of man. the only one that would be problematic in the terms you have described are conflicts against other fellow humans. and that really depends on what side of their ire you are on.

whichever side they happen to be on, the wee humans will come out and want to shake their hands, and give thanks to them. the Imperium is dotted with tall statues, not just of real 'humans' but of Astartes that have come to their salvation. they are looked upon with a mixture of fear, awe and respect.

pertaining to traits of humanity. you brought up genocide and other atrocities. even the Marines can realize an atrocity when they see it. you yourself cited the new Space Wolves codex and their outrage at Armageddon. others have been cited throughout 40k lore of atrcoities great and small and the Marines rising to the occasion of outrage. even when they have been committed by other Marines. the World Eaters often brutal purgings was a shock to many other Marine chapters. the Blood Angels have been seen as being butchers also by their peers.

no i think atrocity is the same to the Marines also..but this depends on what that particular CHapter ethos is and their particualr way of seeing combat and conducting warfare.

A good atrocity for any kind of story is built upon what the viewers experience, compared to what previous knowledge they have. I find it most rewarding to present the characters with several different views on any conflict, to let the players decide for their characters whose side they would like to see as the lesser evil or the greater good.

The example of modern day military personel above was interesting, I'll use it to illustrate by an example. Lets say I am a soldier that returns fire when being shot upon. My return fire hits a building that turns out to be an orphanage. Do I think I commited an atrocity? Probably not, because I had no idea there was a higher than normal risk of civilian casualties. (Will I have nightmares over what I've done? quite likely) Do I think my intended target commited an atrocity by attacking me from that position? Maybe, if I believe she knew there was an orphanage there. I might even believe she hoped it would give her an edge. Do I think that one of my officers up the chain of command comitted an atrocity by deploying me nearby this orphanage? Maybe, but would it have been a bigger atrocity to not deploy me in this spot and thus fail to imply my sides (completely justifiable and totally righteous) protection to this location?

Do the same thoughts for my opponents. And then do them for the 7 years old that just got his best friend, and his closest thing to a family, shot by me. Do we have different views? Indeed we do. Is there an "objective truth" in this situation? I think not.

Apply this to your players characters. Place them in situations where there is an overload of conflicting views, and make some of those views be things like: "The Ultramarines surely knows what they are doing. It warms my heart that they are abandoning us to be eaten by tyranids, because then they must be doing something much more important." Mix that up with: "the ultramarines are all about PR, now they got their glory shots from when they rescue kids from a burning hospital. Nevermind they set it on fire in the first place, looking for "traitors". Now they are done with us and they are off again, leaving us to be eaten by tyranids." Or maybe even "The spacemarines are the ultimate symbol of the corpse emperors opression of humans everywhere. It is only to be expected that they leave s to be eaten by tyranids" If this is done correct you will get a very nasty feeling of a grimdark universe where there is little left worth fighting for. I like that feeling, it breeds desperation and makes our RL-world look a bit shinier.