I have been running an only war game for a couple months and have been having some fun with the group battling the Dominate. What I thought of for what could be a good arc came from DH. They mention a group called the Logicians, basically former members of adeptus mechanicus that are more secular and innovate and design new tech, seeing the precepts as too limiting. I started wondering if the Dominate would offer them a place, basically areas to practice their research in freedom and offers of things to do said research in exchange for special weapons or tech. That and I had a bit of a brainstorm involving them deciding to make some of his elite troops glad warriors as low rent space marines to buy more time for his armies. Unfortunately I'm still trying to work out the plans and I could use some thoughts from others if no one minds.

there are skitarii pretorians that are almost equal to marines

i think the duke would encourage the hereteks, he makes deals with dark eldar too so i think he is always looking for opportunities, especially considering that he is fighting a loosing battle mostly

you could also bring out some Legio Cybernetica horrors from the horus heresy to spice things up, a few Thallax and a Castellax as final encounter, which would proof a serious enemy unless your group sports a Leman Russ

if you need inspiration for those two look up the Horus Heresy 2 - Betrayal from ForgeWorld

Depending on the length of this campaign, I have an idea, but it would have to be an evolving background theme that just kinda churns on for a long time and then erupts within the Dominate - not sure how you would narrate that, especially from an outside perspective:

Yes, I definitely think that the Severan Dominate would be liable to ally with borderline hereteks such as the Logicians, or many other groups that might not be Hereteks, but at least Malateks - there's a lot of information in Dark Heresy's The Lathe Worlds , if you've got it.

But they point I want to come to is that, the nature of the Dark Mechanicum vs. the Adeptus Mechanicus is largely esoteric, and limited to those in the position of the know-how.

Assuming that the Severan Dominate has sworn AdMechs on their side, that have forsaken the Imperium, they may be as desperate as the Severan Dominate itself, or maybe already under anti-Imperialist doctrines. Here lies the opportunity of the Severan Dominate, largely ignorant of (or straight-up just ignoring) the finer points of heresy and the Martian Schism, may seek to approach (or be approached by) groups or individuals of the Mechanicus/Mechanicum of wildly varying faiths.

They might approach the Logicians. They might approach the Empyrean Enginseers. But they may also be approached by Malygrisians - remnants of the Malygrisian Tech-Heresy - or envoys of far-flung Dark Forge Worlds under the guise of loyalty. I have no idea if the Severan Dominate has their own titans, but imagine if Traitor Titan Legions showed up, swearing allegiance to the Dominate. Would they accept it? Can they afford not to? Would they even realize that these are agents of the Ruinous Powers?

While at first these two factions - cliques within what would inevitably form a single faction due to their technological inclinations and being the only ones that can fix a tractor - would get along as much as you'd expect the Westboro Baptist Church getting along with Radical Islamists - after all, they'd agree with eachother that God Hates Fags - there would be inevitable chafing, because Malateks are still at a fundamental level likely to still be loyal to the God-Emperor, or at least his tenets, or their idea of those tenets.

The other side, on the other hand, are either wholesale atheists or actively worship daemonic entities.

The Severan Dominate may ignorantly pull all these different little groups of Tech-Priests together for their cause, either by desperately approaching them or because these groups all want protection, but much like in modern-day Europe, all you'll get is balkanization and infighting, because while all these groups have their own agendas, and while all these groups may be at least nominally loyal to the Severan Dominate, they will end up hating eachother over big and small issues.

And as Nightcloak says here above, pulling out some Skitarii Praetorians might be nice, and depending on what group that made them, they might be anything from Augmented Stormtroopers with a range of implants, integrated hellguns and good-craftsmanship cybernetics, to near-Obliterators with daemon-infused Lascannons for arms and Longlases mounted on their shoulders, a twisted hulk of fleshcrafting and machinery.

There are Skitarii written up in Hand of Corruption (BC, so practically the same system as OW) that are very very very lethal even without being Praetorians.

Your biggest question would be who are these other TPs loyal to? Much of the Dominate still professes to be loyal to Him on Terra, if not the Imperium, and let's be honest, from our outside perspective, the Emperor wouldn't be happy with His Imperium, anyway, so the validity of what the Imperium says is suspect. That said, Severus's tech-priests "should" still be loyal to the precepts between Mars and the Emperor, and even Severus "seems" to be an Emperor-loyalist; this might not be so true, and the next gamebook might reveal that, in addition to being a xenos-fraternizing d-bag, he's also just another garden-variety Chaos suck up. With that, he might not like those who openly renounce the Emperor, or want to risk employing them, and having others who serve him find out, and jump ship; losing some just to gain others only works if the new people are rather better, and the ones we're talking about have some serious strings or baggage attached.

As he sinks further into a crazy that, eventually, only Vandire will be able to relate to, he might easily seize up any offers for extra help, but as long as his ignorant tools still think that the Emperor is good, and he doesn't want full-scale secessions from his secession, he might have to be leery of who he allies himself with. He'll also need something to offer back, and he's losing; he can't even get his to RT buddies to throw in real support, and few others can say they'd have less to lose, either by being found out, or falling with the Dominate, when it gets eaten. Someday, maybe, the Imperium will finish fighting in the Reach (HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!!!!!!!!!!!!!), and then call troops in to out this down (or that Callidus will finish sneaking in), or they'll pull back a hair, and just let the Orks do it, then kill them off. Sometimes, I really wonder why the Imperium can't just be a bit more Eldar, and let two enemies happily beat each other, and then swoop in to crush the "winner"?

Oh well, dig for cool AdMech variants, and I hope that they serve you well. Sometimes, it's really cool to see that weird stuff, that otherwise sees little exposure.

Admittedly some of it is simply that I'm a big fan of tech oriented stuff, and I also realized some fun mad scientist potential. The reason I'm mostly using the logicians is frankly that they aren't likely to be running around to the public, they are also going to ultimately be loyal to themselves. They're going to use the Dominate as their beta testers for various tech as well as get some actual working forges and the like to do their experiments with, not to mention that a few members of the logicians that are biologis focused can try some of their experiments (after all, the Dominate is probably going to be desperate for anything to beef up its troops).

Currently I have plans for an extended campaign, I want to run Final Testament because I like the adventure, but afterwards they are going to be on a Dominate world and if they are able to take one of the manufactorums they will, with a fair amount of digging, discover that there were experiments being done trying to create a variant on the dark lances. Now that might freak the players out a fair amount once they learn about it but that is only one part of it. See Biologis has some ideas of their own and they're curious, and there are going to be some noble soldiers willing to give their all...so we end up eventually with some of them becoming gland warriors that have a few special induced mutations that they need to eat a certain food to maintain their strength and survival (the Logicans aren't stupid, they are going to have a few things that the Dominate will need to make sure they're unlikely to be sold out...which might lead to the dominate accepting offers from a different mechanicus group, and then another...)

Not to mention that if the group ends up going one of the possible routes offered in Final Testament...well I wouldn't mind trying to work out a techguard campaign.

Edit: I'm looking for any other thoughts though, and I do love some of the potential madness that can come with the addition of multiple schismatic factions within the dominate.

Sure, the Logicians make a fine addition to the Dominate.

You know who else?

The Inquisition, especially the Istvaanians!

After all, war is needed to strenghten the Imperium.

While they may not make an open appearance they could easily send information about targets, sabotage communication and other things.

Let your squad get caught up in such a thing, where High Command seems to have screwed up very badly and they only get away with the skin of their teeth. And in the following investigation by the Commisariat they get questioned and get curious about it as well. Why not do a little snooping? Unless they want another Mara Landing Massacre.

I sometimes forget that there are Inquisitors who are "loyal" to the Imperium (not radical Heretics), but who basically try to wreck it, or at least not help, in an effort to improve upon it; you can't know how strong your bridge is till something crosses it, till you hang some stuff from it. Better know now than when lots of things are using it.

I do sort of wonder how far some of them can go, though? If they are still loyal to the Emperor, they SHOULD be putting some things into motion to deal with Severus, even as they are "helping" him. Even daemonhost-forging Malleus Inquisitors are planning on using the daemons AGAINST Chaos, and they still plan for the Imperium to be standing, tomorrow. The above could be an interesting, if very cruel, event. I just hope that it comes with the Guardsmen having a little wiggle room to check, rather than just ignore it as drones do, or be told to by their superiors, while a Commissar cleans his bolt pistol barrel.

Ooooh, i forgot another radical faction in the Inquisition: The Recongregators.

Down with the old, clogged Imperium, rebuild it anew.

Other factions that are interested in the war:

The Nobles. I am sure that several Nobles lost their land and property when the Dominate was founded and they surely want it back. Or they simply want it because the previous owners are dead. There could be treasures or vital information still there.

Not to mention the Trade Chartas. After Imperial victory the contracts have to be reinstated or renegotiated. Having a high ranking officer in your pocket to 'liberate' things for you or help you to be the first choice for those.

Lots of reasons for Nobles and Chartas to influence the IG by pulling strings, giving a few presents (better gear and food is always a good way to buy a soldiers/officers loyalty) and placing YOUR officers where they facilitate your plans the best. Competence is not really necessary with the right connections.

And all that influences your squad down there.

Edit: @venkelos: Manipulating orders so that batallions fight each other instead of the enemy like on Mara seems rather easy. The same goes for changing the numbers on an Intelligence Report about a new target, when you attack with far too few soldiers. Giving information about vital supplies to the Orks, Dominate or various pirates is not that hard either. All that means trouble for your squad. So why not give the Commissariat a hand and sniff a few 'traitors' out?