Ok, so I have been a follower of 40k for decades. There is one topic that is somewhat glossed over and that's how large scale wars even occur for any protracted length. I'm trying to wrap my head around and come up with fluff reasons why this would happen for my Rogue Trader game.

The essential question is this: Why doesn't one side eventually gain space superiority and just bombard the living crap out of the enemy ground force, effectively ending the war?

Consider this scenario.

You have an Imperial world that turns traitor for whatever reason. This world has a very large and powerful PDF with fortresses, etc. They also have a large and powerful orbital defenses.

Imperial fleet arrives and destroys or occupies orbital defenses and simultaneously lands forces for a beachhead. Eventually the Imperial fleet would gain space superiority. Why then would they not just bombard the PDF forces into submission?

Let's say that a large chaos fleet arrives and drives off or destroys the Imperial fleet. Why then wouldn't the Chaos fleet bombard the Imperials on the ground into dust?

We know that such things as planetary defense lasers exist but from the fluff they appear to be very large, very static and very power hungry things. I would assume they would only protect fixed bastions and even then, there would not be lots of them. So even then, at best the enemy could only hole up in very limited defenses with really no hope of extrication.

My problem is that I can't seem to conceive of very many scenarios that would allow for protracted land campaigns as we see in 40k fluff all the time. It seems like someone will eventually achieve space superiority by destroying or driving off one side or the other.

Ideas?

You cant in general break an enemy from the air modern conflicts have proven that, so for one an orbital bombardment will not break an enemy or secure the plant also you need those hives and mines for other war efforts and you gain nothing by bombing the planet to dust

I would disagree. Orbital bombardment in the context of what's been presented in rules and other sources would very quickly reduce an enemy army in the field to ineffectiveness. Would it end all resistance? No, but it would either force them to retreat to protected fortresses or reduce the war to a guerilla action.

In the case of collateral damage, I would agree but many fluff campaigns take place in wilderness, rural, open areas or hive/urban areas that are already mostly destroyed.

I'm just having a tough time conceiving of a protracted campaign of maneuver with large fronts, etc.

If bombardments were presented as accurate and effective in a more tactical way then yes i would agree but they are more akin to shotgun blast as opposed to a sniper rifle while they could inflict massive damage to an army in the field if they happen to be standing in the open. But from the books have read there is general a goal in mind that you have to invade or there is not a large naval element in play or so on a so for plot devices. But what I still believe is that a bombardment just is not going to be the end all beat all when attacking a hive world you need the hives to make things so you have to take them on the ground no way around it. But that's just my two thrones

Well, the thing about orbital bombardments is that they do a lot of damage to an inhabitable planet. Inhabitable planets are valuable - to pretty much everyone, and the more damage you do from orbit, the less useful you make the planet.

Also, a lot of conflicts are to take/hold/reclaim objectives, whatever they may be. It is not uncommon for valuable objectives to have some form of passive defense, most commonly city-scale void shielding, or being built underground, or occupying a middle ground being insufficiently valuable to have shields, yet both valuable and soft enough to preclude orbital bombardments from being used in their vicinity.

The most common reason for large scale planetary combat is because you want the infrastructure intact, or mostly so, for your own/future use. You need ground forces to take on the opposing ground forces.

In addition, planet-based anti-space defenses will effectively protect an area around them against orbital bombardment, and require ground forces to be neutralized. For a sufficiently valuable/well defended world, it is possible, even likely, that there will be near-complete coverage over all landmass, and a fair chunk of oceans, depending on the land/sea ratio and distribution.

The Navy doesn't see much point in risking its ships getting shot up to suppress planetary defenses when the groundpounders of the Guard can do it. Thus, the Navy will punch through and hang around in low orbit for the Guard to get the first wave down and establish a beachhead, and then the Navy will usually pull back, and out of range. This presents a role for specialized planetary assault ships - for suppressing defenses and establishing beachheads, and sometimes hanging out in geostationary orbit or a lower, powered, orbit hanging over the beachhead to support operations.

And, if it's your own planet, and you're shipping in Guard forces to resist invaders, well, you want to minimize the damage to your valuable inhabited planet, and orbital bombardments are pretty much the opposite of minimizing the damage.

In addition, if there's an enemy ground force big enough for a field battle, it's likely that the enemy has its own naval support, and while neither side may be able to drive the other out of the system, or take and maintain control of the orbitals, it's likely that if one side attempted to engage in an orbital bombardment, they'd leave themselves vulnerable to counterattack.

In addition, if there's an enemy ground force big enough for a field battle, it's likely that the enemy has its own naval support, and while neither side may be able to drive the other out of the system, or take and maintain control of the orbitals, it's likely that if one side attempted to engage in an orbital bombardment, they'd leave themselves vulnerable to counterattack.

This last point is a good one. I forgot that they tend reserve committing to large space battles unless it's absolutely necessary or they have great odds. So I can see where a local stalemate in space might develop.

I think the rules for a planetary bombardment are in BFK, and it would seem it's a slow and difficult process which leaves a ship vulnerable and warp capable ships are an extremely rare and expensive resource. Looking at the potential pf of a hive from SoI, a ship is worth at least 3 fully developed hive worlds.

Also, planets are vast. The amount of time and munitions it would take to remove an invasion force soly with bombardments, especially if it was planet wide

Also, there are lots of surface-to-orbit weapons in 40k, and it's way cheaper to field macrobatteries/missile silos/void-capable aircraft on the ground than to counter it with naval firepower, making planetfalls the only way of securing the planet without losing half of the battlefleet.

Surface defenses...check.

Desire to capture planet intact...check.

Ineffectiveness of orbital bombardment short of very destructive...check.

Sometimes you just have to dig them out. Don't read too much sci into this scifi game. It will leave you scratching your head.

Between numerous anti-orbital defense emplacements, and let's not underestimate how much resource the Imperium is willing to dump into such things, with threats like Orks and Dark Eldar around, numerous torpedo silos, space-based defenses, such as stations, and guard ships, and void shields, taking a planet can be hard. With your scenario, Only War should be about as done in practice as its game line is vaguely hinting that it might be. Severus does NOT, for the most part, have space forces, as the navy is his enemy, and his few Rogue Trader allies are not willing to piss off the Lord Sector to help him in that field. He does have numerous fortified bastions, defended with redundant defense lasers, missile/torpedo silos, and more, all hidden under redundant void shields, and sitting atop buried, reinforced, Proteus-class command bunkers. His troops are dug in, and the Imperium's ground forces can't dislodge him, nor can their space-based assets bombard his troops, for fear of hitting their own. While they are sitting there, in low orbit, trying to take shots at his bases, or trying to deploy mass-troop transports to the surface, those bases are firing back, lobbing torpedoes, lances, and macroshells into the Navy's ships, which can't survive the fusillade. They might be able to own the space around the planet, but they can't achieve true superiority, beyond stopping incoming supplies.

This is why I hope, personally, that the Duke will get taken down by a cleverly deployed Callidus or Vindicare Assassin, because safe under 5 void shields, a building that can survive bombardments, 100 feet of earth, and the walls of his subterranean bunker, I'm not sure what else will kill him. Also, the Navy's vessels are a limited resource, like Space Marines; they only have so much food, so many shells, and need to go do other things, with the Imperium fighting a separate war for every star in the sky.

Strategically, Heinlein said it best: While the technology to destroy a world exists; this is rarely a desirable outcome! Far more likely is the need to take a world for it's resources or some other intrinsic value. Voidships alone can rarely achieve this. For example: If your desire is to take a Hive city; Orbital bombardment would destroy the Hive and all it's Manufactorums and other resources long before you were able to reduce the local PDF garrison to the point of surrender. And that's without your typical Hive's Battleship Grade Void shields and surface to orbit defence weapons! While such things could technically be rebuilt over time, They would certainly NOT be available for an ongoing crusade or provide any PF from the settlement!

Tactically, There are very few Voidship weapons that can be effectively used in a ground combat role. In fact, there are only two I can think of: The Torpedo (Pinpoint accuracy, Limited destructive radius but can be intercepted on the way down [ DW: RoB, pg. 216]) and the Bombardment cannon (No Actual stats but fluff in novels suggest the following: Torpedo like accuracy; inability to be intercepted and a Variable yield warhead ranging from torpedo to Lance in effect). Lances are occasionally used in the battlefield support role but this is more like deploying a tactical nuke! Lances Are also Horrifically inaccurate in the Ground attack role (Either DW: RoB, pg. 215 or RT: BFK, pg. 133 ). Macrobatteries affect an area of some 10 square Km. ( RT: BFK, pg 133) and suffer the same innacuracy issues as lances (If not worse!). As such, they would not likely be used in a ground support roll. (Although they are Ideal for strategic bombardment and pre-landing Naval gunfire support!)

If the Planet can be taken by surgical removal of it's defenses and command and control structure then Astartes backed by their integral naval support are Ideal (It's what they specialize in doing as a matter of fact!) and operate pretty much as Izrador suggested earlier. Unfortunately, this is often not viable for a variety of reasons. When this is the case, The Imperium is faced with two choices: Exterminatus or major ground war. Since few Imperial commanders are willing to commit to destroying a strategic asset for no gain; the choice has already been made for them. That choice is to send in the Imperial guard and brace for a long war!

Mind you, they ram one into a star fort that could be fairly easily bypassed just to deliver two regiments tasked with retaking the thing.

Space to ground weaponry in 40k has been portrayed fairly inconsistently (go figure) but it is NOT a 'shotgun to sniper rifle' comparison. Orbital bombardment has been shown to be fairly precise.

As long as you're using Lances or bombardment cannons.

See, this is the issue, Bombardment cannons got shoehorned into macrobatteries in BFG because they wanted them to have to use the gunnery table to avoid them being 'lance by another name' for space combat. In fluff, (and other games) bombardment cannons and lances are highly precise, able to hit individual buildings and provide a certain amount of direct fire support, leveling individual bunkers and hard points. (See various BL novels, Codex: Planetstrike, so on and so forth)

For some reason (I suspect Horizon's involvement in Battlefleet Koronus and balance issues) we got the reverse of how Bombardment Cannons work in fluff and every other game, with them saturating an even wider area than regular macrocannons. (Though, as we see in Nightbringer , a defective shell can land several hundred miles off target)

Lances, in fluff, anyway, are highly effective against ground based fortifications, though it make take several shots for deeply buried and shielded locations. In Cain's Last Stand , for example, lances are used in a decapitation strike on the PDF headquarters on Perlia. However, collateral damage is still pretty severe in both cases. While a lance's strike zone is only a km across, (at least in this game), Cain observes how windows shatter several km away.

Edit:

Radwraith, the problem is that does not match the rest of 40k, and was done for the reason of balance (and possibly Horizon's headcanon). Lets actually stop and think about it, a strike cruiser is, supposedly, built from the ground up as a support ship for a small SM strike force. they would have little use for wide area bombardment. What they would have a lot of use for is precision strikes against hard targets. And we see this both in Codecies and in BL novels.

Mind you, they ram one into a star fort that could be fairly easily bypassed just to deliver two regiments tasked with retaking the thing.

Space to ground weaponry in 40k has been portrayed fairly inconsistently (go figure) but it is NOT a 'shotgun to sniper rifle' comparison. Orbital bombardment has been shown to be fairly precise.

As long as you're using Lances or bombardment cannons.

See, this is the issue, Bombardment cannons got shoehorned into macrobatteries in BFG because they wanted them to have to use the gunnery table to avoid them being 'lance by another name' for space combat. In fluff, (and other games) bombardment cannons and lances are highly precise, able to hit individual buildings and provide a certain amount of direct fire support, leveling individual bunkers and hard points. (See various BL novels, Codex: Planetstrike, so on and so forth)

For some reason (I suspect Horizon's involvement in Battlefleet Koronus and balance issues) we got the reverse of how Bombardment Cannons work in fluff and every other game, with them saturating an even wider area than regular macrocannons. (Though, as we see in Nightbringer , a defective shell can land several hundred miles off target)

Lances, in fluff, anyway, are highly effective against ground based fortifications, though it make take several shots for deeply buried and shielded locations. In Cain's Last Stand , for example, lances are used in a decapitation strike on the PDF headquarters on Perlia. However, collateral damage is still pretty severe in both cases. While a lance's strike zone is only a km across, (at least in this game), Cain observes how windows shatter several km away.

Edit:

Radwraith, the problem is that does not match the rest of 40k, and was done for the reason of balance (and possibly Horizon's headcanon). Lets actually stop and think about it, a strike cruiser is, supposedly, built from the ground up as a support ship for a small SM strike force. they would have little use for wide area bombardment. What they would have a lot of use for is precision strikes against hard targets. And we see this both in Codecies and in BL novels.

Ra

Did I write that poorly Baron? I thought I said the same thing! I realise that the only mention of the Bombardment Cannon in BfK works exactly the opposite of how we've both read about it in other sources. That's why I suggested (Read: Houseruled) what I did.

As to Astartes not having a use for "wide area bombardment weapons" I respectfully disagree! I have always believed that this is a large part of the Astartes legendary prowess. A Battle company can seize a critical location and potentially even defeat a 'normal' force even ten times size (With good tactics and dice rolls )! The problem is when larger forces arrive. There is literally no way a force of 100 or so space marines is going to win against a force of thousands! What they can do however, is use the Strike cruiser to annihilate said relieving forces when they expose themselves to move in on the Astartes. A regiment sized forced on the move could easily be detected and engaged by an orbiting Voidship. Hence the truth behind the Legend: A Company of Space Marines can conquer a world!

These are all good replies and are giving me good ideas. Thanks.

Between numerous anti-orbital defense emplacements, and let's not underestimate how much resource the Imperium is willing to dump into such things, with threats like Orks and Dark Eldar around, numerous torpedo silos, space-based defenses, such as stations, and guard ships, and void shields, taking a planet can be hard. With your scenario, Only War should be about as done in practice as its game line is vaguely hinting that it might be. Severus does NOT, for the most part, have space forces, as the navy is his enemy, and his few Rogue Trader allies are not willing to piss off the Lord Sector to help him in that field. He does have numerous fortified bastions, defended with redundant defense lasers, missile/torpedo silos, and more, all hidden under redundant void shields, and sitting atop buried, reinforced, Proteus-class command bunkers. His troops are dug in, and the Imperium's ground forces can't dislodge him, nor can their space-based assets bombard his troops, for fear of hitting their own. While they are sitting there, in low orbit, trying to take shots at his bases, or trying to deploy mass-troop transports to the surface, those bases are firing back, lobbing torpedoes, lances, and macroshells into the Navy's ships, which can't survive the fusillade. They might be able to own the space around the planet, but they can't achieve true superiority, beyond stopping incoming supplies.

This is why I hope, personally, that the Duke will get taken down by a cleverly deployed Callidus or Vindicare Assassin, because safe under 5 void shields, a building that can survive bombardments, 100 feet of earth, and the walls of his subterranean bunker, I'm not sure what else will kill him. Also, the Navy's vessels are a limited resource, like Space Marines; they only have so much food, so many shells, and need to go do other things, with the Imperium fighting a separate war for every star in the sky.

That inffectiveness against planetary defenses is why the Navy pounds a hole for the Guard to establish a beachhead, and maintains a corridor for the Guard transports to get enough forces on the ground to punch out/disable planetary defence centers to leave a gap in the planetary defense coverage to pour the rest of the ground troops in while the Navy pulls its ships out of range, and leaves the war to the Guard to finish. This is entirely in accordance with Navy policy and traditions. Sure, the Guard is going to be slow, and go through lots of bodies, but with even a small gap in coverage to funnel reinforcements through, they'll eventually be able to plow through the defenses on the ground, without the Navy needing to do more than ensure that the transports get there and keep Severus's limited naval assets from being able to subject the Guard beachhead to orbital bombardment. As far as the Navy (and Munitorum) is concerned, expending Guard Regiments is better than Navy ships taking lots of damage. Frankly, I'm not entirely sure what the ratio of expended Guard Regiments to Navy damages is, but you'd need to have to burn through a lot of Guard regiments, and probably a lot of time, before the Navy taking the damage to engage in a sustained bombardment would be considered more cost effective/efficient; plus, it is possible, perhaps even likely, that the projections for the Guard operations are optimistic. Remember, Manpower is cheap. Machinery is expensive.

This is a prime example of exactly why there are lots of ground battles. Sure, the Imperial Navy can easily establish space superiority over basically any of the Dominate worlds they want, whenever the Navy wants to. They're still not going to take their ships into the engagement basket of the planetary defenses for any longer than absolutely necessary to establish a beachhead and a gap through the defense coverage, which is vastly less time than would be required to use orbital bombardments to completely break the Dominate defenses. This is even without the fact that the Imperium wants to take the worlds controlled by the Dominate mostly intact, for its own use.

On the subject of bombarding, are there any stats for "modern" cities? What are their defences? Offences?

On the subject of bombarding, are there any stats for "modern" cities? What are their defences? Offences?

The closest official stats to a city, semi-fortified or otherwise, is probably the landship cities of Zayth in ... Lure of the Expanse, IIRC.

Or Stars of Inequity might have some details on individual defensive components in the colony generation system, but I think they were mostly left abstracted.

Biggest issue with the whole 'bomb them into the stone age' idea is that you want to preserve the infrastructure.

When you can blow up entire continents from orbit, you don't leave much standing. You might want the biosphere or even the infrastructure of the planet reasonably intact. A landwar is more likely to deliver that than bombarding the planet.

Or you might have a landwar on already, you don't want to kill the loyalists.

There might be other things of value, archeotech, valuable resources, etc. The last thing you want to do is **** over those things. The population is expendable, the planetary resources are not. You want to clear out the population as much as possible and then put in your own colonists rather than just kill everybody and everything on the planet.

Biggest issue with the whole 'bomb them into the stone age' idea is that you want to preserve the infrastructure.

When you can blow up entire continents from orbit, you don't leave much standing. You might want the biosphere or even the infrastructure of the planet reasonably intact. A landwar is more likely to deliver that than bombarding the planet.

Or you might have a landwar on already, you don't want to kill the loyalists.

There might be other things of value, archeotech, valuable resources, etc. The last thing you want to do is **** over those things. The population is expendable, the planetary resources are not. You want to clear out the population as much as possible and then put in your own colonists rather than just kill everybody and everything on the planet.

For the most part I agree exept for one small part: The population is not expendable per se. Not for any humanitarian reason though. An individual is expendable. A population is a resource! (Manpower). Destroying entire populations, even primitive ones, is a waste of resources. You are very likely to tick off someone very high up if you make a habit of it without good cause. This is another reason why many lord Generals will throw literally millions of guardsmen into a meat grinder rather than commit to exterminatus. It is only when all hope is lost, such as the terminal phase of a Tyrannid invasion, will a world burn. And that is primarily to deny it to the enemy!

Granted, but if the imperium has to choose between say, the valuable manufactorium of a hive world, and the billions upon billions of people living there. Chances are they'd choose the manufactorium and just ship in new population after releasing a brief virus bomb assault and letting the plague burn itself out afterwards.

Also, it's a LOT easier to destroy infrastructure from orbit than it is armies and populations. Populations can hunker down, spread out, rebels can disappear to areas not able to be targetted easily from orbit, and the only way to easily kill them off is to do lots of collatoral damage to the parts of the planet you DON'T want to destroy.

Thus, easier to send in the IG who, while they might shell the hell out of a city, will almost certainly leave it more intact than a macrocannon battery would.

Granted, but if the imperium has to choose between say, the valuable manufactorium of a hive world, and the billions upon billions of people living there. Chances are they'd choose the manufactorium and just ship in new population after releasing a brief virus bomb assault and letting the plague burn itself out afterwards.

Virus bombs are more destructive than just against biological targets. http://wh40k.lexicanum.com/wiki/Virus_bomb

Even ignoring the particularly incendiary properties of the Life-Eater Virus, any virus that wipes out all life in a hurry is going to leave lots of unattended infrastructure lying around. Some of that infrastructure will still be running, unsupervised. Some infrastructure, like power plants and sewage systems, are left running by default, and it's unlikely anyone in the middle of a bio-weapon apocalypse is going to bother to shut them off as a courtesy to whoever's going to inherit their homeworld after everything they know and love is finished dying a slow and painful death. Even small things like ovens can start fires which, without any fire departments left to fight them, could grow to consume an entire city. Even if a virus bomb only directly targets organics, the material damage is still going to be on par with heavy shelling, and if you send in the Imperial Guard it is very much unlikely that every valuable piece of infrastructure will be shelled. Some of it will be underdefended and captured by ground troops without the need to bring out the big guns, and some of it may be held by garrisons who retreat to a more defensible position or surrender entirely.

Depending on the world you may be able to 'starve' them into surrender. A hive world for instance is generally unable to produce sufficient food to feed all of the population so with a space fleet you could blockade the system and prevent them from getting the food they need to feed everyone and wait for infighting and the like to reduce any resistance. You may even get people in power on the planet faced with food riots and calling to negotiate.

That said the blockade will only work if you've got time and even then it will only work against some targets. Orks with their portable ecosystem are unlikely to be starved into submission even if they've taken over a forge world and there is no agriculture to speak of on the planet.

I dunno man, corpse starch is a thing in the 40k verse. A hive world of billions of people wouldn't be self sufficient (usually) but widespread violence would mean more starch rations for survivors.

Also, cannibalism's always an option. It is 40k after all.

Also, cannibalism's always an option. It is 40k after all.

What about second breakfast?!