How well would a space marines weaponry fair against a modern battlefield?

[Elheru Aran]

^ All true... however there is one thing that Space Marines do excel at versus regular infantry... they are often described as moving *very* quickly. A lot also depends on context; would an OPFOR be willing to shell Space Marines if they are in their own city/town?

Also: While arty is important, it's most useful in certain limited contexts. When it comes to urban warfare, you need precision hits to avoid collateral damage. If collateral damage isn't a concern, then yes, artillery is useful, but otherwise, you need either air support or laser-guided rounds.

The Astartes aren't dumb, either. They're as capable as anybody else of going to ground when they hear a barrage coming in, and they aren't just going to cross open ground unless it's some peculiar situation like tree-less prairie/steppe around a city or whatever. Frankly, if Space Marines are legging it very far in general, something's broken down; there's a reason they have Thunderhawks and drop-pods.

[Sea Skimmer]

People are always willing to blowup their own cities if they need to do so to build an enemy. Collateral damage is a political problem when you go invade someone else, nobody actually cares that much. We don't build PGMs to avoid collateral damage, we build them because they just destroy the stuff we want destroyed better.

[LaCroix]

Still, if you are giving the modern infantry access to their artillery and air support in factoring in their efficiency against an SM attack, then you would just as well need to factor in that the SM would have their vehicles, air support, AND at least one significant orbital gunplatform on their side...

I would say orbital bombarnment trumps artillery support. Just to start with, they could crater all airstrips and hangars in a wide area (LOS from orbit) to suppress enemy aircraft, and then do counter battery fire from the ultimate safe, elevated position, destroy any enemy formations visible from above, disrupt vehicle columns, etc...

[Cykeisme]

The most important source of firepower, the weapon that wins battles, and which inflicted the most casualties in all regular wars since the Secession War is artillery. And I don't see a Space Marine force, no matter what their tank support is, walking fine and dandy from a barrage of thermobaric or AT submunition rocket artillery, or after being heavily shelled by 203mm howitzers.

I don't have any doubt that heavy sustained bombardment from our high-caliber artillery will easily inflict casualties on power-armored 40k guys, those are huge guns.

Out of curiosity, though:
What's the average velocity and mass of shell fragments generated by modern artillery shells?


That said, they are equipped with air-mobile ("space-mobile"?) vehicles, capable of multiple SSTO trips on a single fueling, which they can use to land at any point on the planet.. with transit times within an hour, if they have the delta-V to achieve orbit. I don't see us being able to get artillery in place to counter that level of strategic mobility, unless we set some sort of camouflaged trap to lure them into landing, and then prevent them from evacuating while we kill the landed forces. Since the OP does state that this is on a modern battlefield, I assume that they've been brought to battle somehow.

That sort of leads into what LaCroix pointed out:
The reason why they don't deploy any ground-based artillery aside from Whirlwinds (lightweight MLRS platforms), is because their own heavy artillery comes in the form of bombardment from ships in orbit. In fact, part of the heavy ship-mounted armament of all Space Marine capital ships is purpose-designed for surface bombardment. Ordinarily, against 40k foes, providing constant fire support probably isn't always possible due to contested orbital space (I suppose "space superiority" becomes a thing).. but we don't really have any way to deny a space ships the freedom from bombarding with impunity, either as an equivalent of strategic bombing, or as tactical artillery support.

Aside from counter-battery fire and disruption of any of our facilities capable of launching aircraft, I think in fluff they're capable of precise bombardment with the aid of a ground observer, allowing "danger close" support.


Also, regarding the possible logic of any good reasons that Space Marines were designed to be bigger than humans (which, prior to this, made no sense to me) that was just discussed..
Would the square-cube law actually work to their advantage here?
Assuming they do have the necessary strength and sustained mechanical power output to hump the mass/weight of carried ordnance, then an increase from 5 feet 10 inches up to (let's say) 7 feet 6 inches would be a 28% increase in height, but a 65% increase in the volume of any proportional equipment that they're carrying.
Since they're broader too, that might increase the plausibly carried equipment volume a bit more beyond that.

[Zixinus]

When I was referring to greater carrying capacity, yes that might mean more armor, but I was thinking mostly of weapons. There is something to be said for a single individual carrying a weapon that otherwise would require two or more people to operate due to sheer weight and bulk. Even if it comes at the expense of greater size (=greater target).

[U.P. Cinnabar]

The most important source of firepower, the weapon that wins battles, and which inflicted the most casualties in all regular wars since the Secession War is artillery. And I don't see a Space Marine force, no matter what their tank support is, walking fine and dandy from a barrage of thermobaric or AT submunition rocket artillery, or after being heavily shelled by 203mm howitzers.

I don't have any doubt that heavy sustained bombardment from our high-caliber artillery will easily inflict casualties on power-armored 40k guys, those are huge guns.

Out of curiosity, though:
What's the average velocity and mass of shell fragments generated by modern artillery shells?

No figures on velocity or mass of she'll fragments, just a note the heaviest likely Western arty encountered will be 155mm rifles, and MLRS systems,

That said, they are equipped with air-mobile ("space-mobile"?) vehicles, capable of multiple SSTO trips on a single fueling, which they can use to land at any point on the planet.. with transit times within an hour, if they have the delta-V to achieve orbit. I don't see us being able to get artillery in place to counter that level of strategic mobility, unless we set some sort of camouflaged trap to lure them into landing, and then prevent them from evacuating while we kill the landed forces. Since the OP does state that this is on a modern battlefield, I assume that they've been brought to battle somehow.

We have ASAT weaponry which might be of some effectiveness, as well as ICBMs which can reach orbit.

Likely, though, the Astartes force invading a world would also have Guard and Naval support, or more than one Chapter will be in on the operation, if there is a dire threat on Earth which specifically requires the presence of the Astartes, such as a Tyranid, Necron, or Chaos incursion.

Otherwise, a routine invasion will simply see the Guard deployed, and, for most ops, they're more than sufficent.

That sort of leads into what LaCroix pointed out:
The reason why they don't deploy any ground-based artillery aside from Whirlwinds (lightweight MLRS platforms), is because their own heavy artillery comes in the form of bombardment from ships in orbit. In fact, part of the heavy ship-mounted armament of all Space Marine capital ships is purpose-designed for surface bombardment. Ordinarily, against 40k foes, providing constant fire support probably isn't always possible due to contested orbital space (I suppose "space superiority" becomes a thing).. but we don't really have any way to deny a space ships the freedom from bombarding with impunity, either as an equivalent of strategic bombing, or as tactical artillery support.

Aside from counter-battery fire and disruption of any of our facilities capable of launching aircraft, I think in fluff they're capable of precise bombardment with the aid of a ground observer, allowing "danger close" support.

Also, the Astartes are not meant to be regular line troops. They're shock troops/special forces, sent in when the shit hits the fan, generally Chaos or high-level Xenos style, in which case they have the minimum augmentation(cybernetic and genetic)and gear necessary to deal with such threats, as determined by the Codex Astartes.

If they need more firepower than their own battle barges, strike cruisers, and escorts can provide, they either get support from the Guard--who have an impressive array of field artillery--and the Holy Fleet...or, they pray to the Emperor to see them through the mess they've been dropped into, and He answers prayers in strange and perverse ways. Just ask the Salamanders .

(The Ultras, on the other hand, can call on support from within Ultramar, if need be. Even, then...)

Also, regarding the possible logic of any good reasons that Space Marines were designed to be bigger than humans (which, prior to this, made no sense to me) that was just discussed..
Would the square-cube law actually work to their advantage here?
Assuming they do have the necessary strength and sustained mechanical power output to hump the mass/weight of carried ordnance, then an increase from 5 feet 10 inches up to (let's say) 7 feet 6 inches would be a 28% increase in height, but a 65% increase in the volume of any proportional equipment that they're carrying.
Since they're broader too, that might increase the plausibly carried equipment volume a bit more beyond that.

They're giants designed to take on/be gods, initially the latter, til Horus and Abbadon turned traitor. Girlyman is supposed to have introduced new and improved Astartes better able to handle the types of missions the Space Marines get handed.

As for their carrying capacity, they can carry some impressive firepower if they're Devastators, las cannon, rocket launchers, autocannon, meltas, various heavy bolters, and the like, but nothing as big as battle cannon(M3 heavy arty from 12cm on up). You would have to have something as heavy as a Tau battlesuit designed for an Astartes for that to be a remote possibility.

[Cykeisme]

No figures on velocity or mass of she'll fragments, just a note the heaviest likely Western arty encountered will be 155mm rifles, and MLRS systems

Well, I was thinking.. although I'm sure that heavy artillery will be able to inflict casualties on power armored Astartes in the open*, I suspect that the effective casualty radius for each shell detonation will be significantly reduced compared to what we're familiar with when firing at conventional infantry. Like.. I'm hypothesizing that, at certain particular given distances from the detonation where shell fragment pattern density and velocity would essentially induce near-absolute casualties on infantry, it might have near-zero effect on troops that durable.. even if closer proximity to detonations would cause casualties among power armored superhumans as well.

* As was already stated by Elheru Aran, it's an understatement to say that they have quite a bit of experience with warfare, both as individuals and as an institution. They know how to avoid getting into excessively hairy situations unless the risk is necessary, and they know the absolute best response when they do get into a hairy situation, finding the most effective cover and such.

We have ASAT weaponry which might be of some effectiveness, as well as ICBMs which can reach orbit.

ASAT weaponry might be able to reach a strike cruiser in orbit, but I doubt the payloads are sufficient to threaten the armor on a 40k capital ship, since they sling kilo- or megaton level ordnance at each other in salvos.
ICBMs could indeed be a viable threat; they have point defense (the "turret rating" in Battlefleet Gothic), but the existence of some risk might very well be sufficient to at least get their ship to vacate the positions that are optimal for delivering accurate support bombardment.

Also, the Astartes are not meant to be regular line troops. They're shock troops/special forces, sent in when the shit hits the fan

Probably the best point, and the most relevant to the question.
The OP is a question regarding how they'd fare against modern troops on a battlefield, but arguably, they wouldn't even face troops on a battlefield in the first place, not in the conventional sense. That's the role of the Imperial Guard.
They might perform decapitation strikes on identifies command staff, destroy tactical and strategic logistical targets etc, to cripple a modern army's ability to wage war effectively, but their mobility means they wouldn't have to face a vastly numerical military in pitched battle.

As for their carrying capacity, they can carry some impressive firepower if they're Devastators, las cannon, rocket launchers, autocannon, meltas, various heavy bolters, and the like..

Good point, their ability to carry weapons (and the required ammunition/power supplies ) that are normally considered crew-served, or even exclusively vehicle-mounted, is already pretty well known. The insight from this thread is that this capability is not just a function of their strength (to haul more mass), but also their bulk (to haul more volume).

[NecronLord]

An Imperial starship could literally outrun ICBMs if it chose to. As in, turn about and accelerate beyond what they're capable of and at the same time be firing teraton volleys into the planet. These things clip about at high percentages of C sometimes, ICBMs are single figure gravities.

Lorewise a marine ship is typically designed around bombardment as its primary mission, to the point that the most characteristic gun on them is the 'Bombardment Cannon' - a turreted fast firing (by 40k standards) artillery piece designed to provide tactical support in a city which can be dialed down to blow up individual city blocks.

If you're giving them starships, then it's immediately a guerrilla fight at best.

Of course as we're now talking about Primaris chapters too, well, open field combat is going to be interesting given that they have now got void-shielded super heavy grav-tanks with nice efficient autoloaders.

Space marines vs modern forces are going to suffer without orbital support simply because of the diversity of arms that can be used on them and of course the ranges of them. Space marines that can sit in orbit and shatter all industrial production on the target planet then pick off what they want until they are reinforced with more expendable ground troops... won't have problems. Or they could just consume the United States in a single bombardment from their chapter fleet pour encourager les autres.and then receive the surrender of all other governments in the Haig.

[Cykeisme]

Space marines vs modern forces are going to suffer without orbital support simply because of the diversity of arms that can be used on them and of course the ranges of them. Space marines that can sit in orbit and shatter all industrial production on the target planet then pick off what they want until they are reinforced with more expendable ground troops... won't have problems. Or they could just consume the United States in a single bombardment from their chapter fleet pour encourager les autres.and then receive the surrender of all other governments in the Haig.

I think you've pretty much presented the closing statements, which in summary:

With orbital support (from even just a single Strike Cruiser, which is guaranteed to be present if a Space Marine Company is deployed).. we can't catch them, and they can destroy or capture locations with impunity. A combination of orbital observation and orbital bombardment, plus rapid elite troop deployment/extraction using Thunderhawks, drop pods or teleporters, will allow them to do as they please to any strategically or tactically important location on the entire planet, leaving us no ability to respond. ASATs and ICBMs are trivial to outrun or shoot down. We're at their mercy until we surrender.

Without orbital support, they can't accomplish anything, and if the scenario starts with them deployed on the surface, we can basically take our time to deploy and then bombard them with artillery and air power, dogpile them with superior numbers and destroy their numerically tiny force.

Quite simply, they're a force that's designed to attack planets with at least some orbital support, thus presenting a scenario that deprives them of that support means they have no capability to effectively attack a planet-scale target.