Right, I'm going to be detailing the typical Order of Battle of a typical Astartes Battle Company, as well as the primary ways to deal with a significant Space Marine force and some analysis into the kinds of forces that the Verdant Cult will need to develop if it hopes to survive an encounter with an Astartes Battle Company.
The Command Squad
A Space Marine Battle Company is, like every Company in the Chapter, lead by a
Captain, a multi-centennial veteran of war, who has likely fought in thousands of battles and murdered many thousands more aliens, heretics, dissidents and other highly capable soldiers and murderers in his time. Young Captains are a possibility, but even inexperienced Captains are still at the very least Mid-Tier Heroes. A Space Marine Chapter is hamstrung by many things, but it does
not select for incompetency in its Battle Company Commanders.
Supporting the Captain, there is the
Chaplain, himself a highly experienced Marine typically selected from the Veterans of the Chapter to manage morale and inspect the Company for diversions in Faith and the outbreak of Heresy. It should be noted that Chaplains don't generally follow the Imperial Faith, because most Chapters are agnostic and consider the Emperor merely an exemplar amongst men (though some
are adherents of the Imperial Faith who consider the Emperor a God), but they
are faithful to the Chapter Cult, they are inspiring, and they are scary motherfuckers.
The
Apothecary is the Company medic, who among other things saves the lives of Marines so grievously wounded that not even their superhuman biology can stabilise them and also knows how to make new Space Marines. Is typically also selected from Veterans, and considering that Apothecaries tend to have to get in up close and personal to recover the Gene-Seed of their fallen Brothers (which is common enough that the Narcethium they use to do that is also a capable close combat weapon) they're probably Vanguard Veterans. Beware.
The
Techmarine goes to Mars, learns about tech, and comes back with cool wargear and a terrifying capacity to create engines of war. Also has two Servo Arms which are used for holding vehicles steady while they perform maintenance. Typically followed around by either Servitors or a Thunderfire Cannon. Heavy fire support. They might not necessarily be chosen from Veterans, primarily selecting from technically inclined brothers instead of particularly experienced ones, but any Techmarine assigned to a Battle Company is probably very experienced.
And finally, the
Librarian is the Company Battle Psyker, and considering that this is a Battle Company, that means that he's an
Epistolary, the highest rank of Librarian short of the Chief Librarian. Which, presumably, also means he has a few Lexicanii following him around doing scutwork and supporting him in battle as a psychic choir. Probably the most dangerous one of the lot, and the second highest priority target amongst the entire Command Squad, because they pack the firepower of a battle tank in a superhuman-sized package, and with the Warp being calmer than it's ever been that means they can do
way more bullshit than they already do in mainline 40k.
The Company
They should be following the Codex standard: 6 Squads of Tactical Marines and 2 Squads each of Assault and Devastator Marines, totaling 100 Battle-Brothers, each squad being lead by a Sergeant. Which is plenty nightmarish on its own.
But wait, there's more! The typical Battle Company
also has 1-2 Scout Squads around, with attached Scout Marines following an experienced Scout Sergeant performing recon in preparation for their own elevation to the Companies, who can also serve in the main line of battle if needed. And they have Carapace Armour, so even the light recon elements of the Company have equivalent armour to the Colony Auxilia. Still, low priority targets either way, that orbiting Strike Cruisers has an auspex and that Epistolary can scry.
But wait, there's E V E N M O R E
Typically, a Battle Company has an attached contingent from the Chapter's 1st Company to provide heavy support where it is required, like if the Company runs into a Space Hulk while on patrol or needs to murder the Warboss of a brewing Waaagh and the Company is already being overwhelmed. The number varies, but considering this is a regular patrol, expect a squad or so of 1st Company Veterans.
So 10 Terminators.
Who are even more unkillable than regular Space Marines.
Yeah, these guys are
also Kill On Sight.
Heavy Metal
The ship they arrive on (probably a Strike Cruiser but has a chance of being a Battle Barge) is of relatively little concern, and the vehicles available to the Company are likely limited. Predators are rightfully considered Light Tanks, being a Rhino with a turret, but their firepower should not be underestimated. Similarly, Rhinos are mostly redundant considering that the typical Space Marine can already run at 60kmph for
incredibly extended periods but they do lend them incredible combat endurance, since they can carry all their ammo and gear instead of needing to be resupplied by either truck or drop pod, plus provide some suppressive fire in a pinch with that pintle Storm Bolter. Whirlwinds are also nasty, being highly mobile missile artillery, but otherwise their role is to support the infantry, not provide a heavy striking arm like the Imperial Guard has with the Leman Russ.
Unless the 1st Company Veteran Squad brought a Land Raider.
If the Veterans brought a Land Raider too, then things are pretty dire. Land Raiders are in the same weight class as frigging
Baneblades, and while their primary role is troop transport, they still carry enough firepower to murder whole villages, and possess some of the most sophisticated Machine Spirits in existence, roughly translating to
they can drive and shoot themselves. And they also can deploy Terminators, if that wasn't enough. If they brought a Redeemer, do not get close. Those Flamestorm Cannon sponsons are nightmares to deal with.
They also have Dreadnoughts but whether they get awoken for a routine cult stomping run is debatable, personally I think they won't show up as part of the first wave, and will be activated later on as the situation escalates. That said, when they do awaken, they're universally selected from heroes of the Chapter, because Dreadnought frames are hella expensive. These guys are, invariably, Veteran level too, except now they are a literal walking tank. Beware.
Doctrine
Space Marines, due to limited numbers and their high quality of training, as well as ready access to seizing the initiative due to various qualities, are extremely proficient in surgical strikes and terror attacks. When your typical infantryman is an 8 ft. tall supersoldier who wears power armour that makes him a walking tank, who can also move as fast as a tank but significantly more agile and also with a smaller profile than a tank, coupled with their legendary reputation and their ability to inspire Transhuman Terror... they are masters at decapitation strikes, surpassed only by Eldar Aspect Warriors, and in many ways they are better at the job, because they have superior combat endurance and so can keep doing it for weeks or months at a time while the Aspect Warriors can only do it for so long before they need to rotate out.
What the Space Marine Chapter typically does, then, is identify HVIPs and hotspots on the world, whether through recon, scrying or orbital auspex (with local militia support), then drop in with either a squad of Tactical Marines via drop pod or a whole bunch more on a Thunderhawk at once, or maybe even infiltrating by ground along the way, depending on how the Chapter feels about the element of surprise. Then they go in, decapitate the enemy leadership, then rinse and repeat until all the enemy is indisarray and the remainder of their job is mopup.
So, to recap, the Space Marine Battle Company is precise enough to perform decapitation strikes and tough enough that most traps set for them are actively baited because there's no real way to kill them short of anti-armour weaponry
anyways. They are, and likely will remain, the premier supersoldier of the 40k setting, because they are extremely versatile and there
is no real way to exploit their weaknesses, because they
have no real weaknesses besides being few in number, which is extremely hard to exploit because given the opportunity they
will inflict disproportionate casualties as they die.
So, how do you kill them?
Fortunately, Space Marines are still (theoretically) human, and humans die to massed firepower. The only problem is holding them down long enough to do so.
How can the Verdant Cult do that?
1) Belladonna spam.
Belladonnas are already noted to be capable of matching a Space Marine in melee, the only problem being getting there. It would be cruel to just spam Belladonnas just for them to die charging across open fields, which leaves fighting on advantageous terrain filled with dead ends, choke points and ambush areas (like a city) and then shooting them full of missiles and plasma.
2) Making monsters
The alternative will be exploiting the hell out of those Life and Death spheres, making organic beasts that can take incredible damage and not die, who can reanimate after they die either to continue tarpitting or potentially as an ambush strat to take down unwary Astartes (insofar as they exist) or, more likely, to serve as a further distraction for our own forces to either reposition or keep shooting. You'd have to go full biohorror for this to work, though, and in the time VM has left it may not be feasible to make these. There may not be enough time left to play with life in this manner.
3) Make peers
One of the few ways to match the Space Marine is with an equivalent. Orks have various flavour of Nob, Eldar have their Aspect Warriors (easiest would be Dire Avenger, being as they are the versatile ones, but any theoretically work), so on and so forth. This is theoretically possible by further developing the Belladonna, like giving them ranged weapons and such, and is my favoured long term strategy. However, in the short term this is likely not viable, there aren't enough Belladonnas to contest a Battle Company even if the upgrade was already in place, and you still have to worry about Terminator Armour and Tanks.
4) Take the initiative (Alternatively: Fuck 'em with Tanks)
If you don't let individual squads of Space Marines go to ground, report upwards or blend into cover, and ideally get them into an open field with no cover that has been pre-sighted with plasma artillery, you can kill them. It's how Imperial Guard and the like deal with Chaos Space Marines if they can deal with Transhuman Terror; open field battles, tanks, meltaguns and plasma cannons. It's not foolproof, and a lot of people will die, but hitting Space Marines at range is a lot safer for you than trying to fight Space Marines in melee, where they have even more advantages. However, considering Belladonnas exist, this is hardly a first resort, not to mention that this will result in mass casualties and we'd fail that secondary objective. And also massive loss of human life.
5) Turn them (?)
This is the unlikeliest option of all, and absolutely requires that the 5th Company of the Azure Dragoons be the same brand of disenfranchised Space Marine described in the opening blurb, who disagrees with the direction the Imperium has taken but is powerless to speak up. Which is very unlikely. And even then, you have to deal with the following facts:
1) Chaos Gods are really fucking nasty
2) The distress call described a Chaos Cult
3) The Forlorn Contingency means that this is already Taken Seriously
Which means that the only way for this to work demands that the Space Marines already have doubts about the veracity of the claims of Chaos Activity, that all attempts at resistance are peaceful or at least not overtly Warpy (bio-tech is pretty fucking weird and may be taken for Warpy btw), that the Governor looks like a fool who panicked and fucked up (which is the easiest part of it all) and that the Battle Company won't just murder all the dissidents
anyways. So, obviously, this is the longest shot of all, which fundamentally requires convincing a bunch of century-old fanatical supersoldiers who have at the very least been raised on tales of Chaos being the ultimate enemy who can appear in any number of forms and is inherently deceptive... That we aren't Chaotic.
In a galaxy that has painted all 'Anti-Imperial' sentiment as Heresy.
Which is an
incredibly long shot.
Naturally, I think we should lead with this. Because the rewards include having a Battle Company as acquiantances.
