"Planetary Assaults" Topic

One of the problems I have with many sci fi battle games, is that they rarely have much going on that is particularly sci fi. 40K is a good example. Call a bolter a rifle, a heavy bolter a machinegun and swap out the minis, and you could run a fair mock up of a WWII infantry skirmish without changing any of the rules.

One aspect of sci fi that I'd really love to see done on the tabletop would be a planetary assault, complete with starships and surface batteries duking it out while the PBI tried to secure a foothold. Anybody know of a rules system that already does this? Note please, that I said ALREADY. No posts starting with "Well, it would be easy to convert 40K…" will be responded to. At least not by me.

BFG + 40K

The planet starts with a certain number of points of defense, the attacker getting a transport so close to a planet for so long allows him to bring on so many points worth of troops in 40K. It's in one of the BFG books.

I had an idea a few years ago about using Full THrust, Dirtside, and Stargrunt in a combined game. I figured I would use the Full thrust rules to initiate the planetary landing then add Dirtside on another table for the ground forces assulting an objective then once troops reach the city, add Stargrunt on another small table for some man to man city fighting. Never really got around to working out all the logistics.

Most 6mm sci-fi games I'm aware of already have rules for planetary bombardment, drop troops, ect…

With Dirtside, it's just a matter of writing the scenario, unless you're looking for detail about the starships interacting in orbit as the battle occurs. If you do need starship interaction I think Full Thrust + Dirtside or Stargrunt is going to be the closest thing you'll find to a pre-existing ruleset that covers these kinds of actions.

Hopefully I'm wrong though. ;)

Epic: Armageddon has an interesting variation on this, where certain Eldar tanks have warp gateways built into their frame, allowing them to drop entire warhosts off without exposing the troops to fire if the tank is destroyed.

One could do it (with time and patience) using the gamut of Renegade Legion titles. Leviathan handles the high orbit activity. Interceptor handles the interface action. Centurion handles the ground action. If you really wanted to go whole hog, you could use Prefect as the map campaign portion. All are available on ebay from time to time.

"Warp Storm" an old BFG supplement was the source of 40k/BFG interface rules. It is looonnngg out of print and written for 2nd or 3rd edition, but OTOH was so basic it would still work.

You start with the BFG action and when Transports (and remember in in the GW 'verse, cruisers are built to carry a regiment each, so it's not just "transports" you can use for the assault) get into "near orbit" they can debark 1,000 points a turn. We decided that 5,000 points was abstracted to a "Regiment" or "Chapter" or "Cadre" or whatever.

After that, make sure the turns are in sync between BFG and 40k. Each 1,000 points dropped from orbit shows up on the 40k table in the next friendly movement phase. Units can move on from the edge or Deepstrike if they have that ability.

Ships in "near orbit" can fire normally at other ships OR choose to shoot one Ordinance Template onto the 40k table S10 AP2, subject to normal indirect scatter rules. (Now that we have Apocalypse rules I would change it to on of the "Orbital Strike" Strategic Assets).

Scenario is VERY important. Make sure ALL the objectives are on the 40k Table to focus the action. A general "Kill Everything" game pretty much ensures that the attackers play way too conservatively for an enjoyable game.

I have used them in a "Big Battles" (before they were called Apocalypse Battles). Pretty basic, but worked well.
My favorite game was when by turn 6 my team's covering fleet had been wiped out and we were sucking up 10 orbital strikes a turn.

We closed up against the enemy to make his strikes dangerous to both sides and managed a draw. Very fun.

One of the GZG books has rules to interface Space and Ground combat with Full Thrust and Dirtside (as well as some older system called Hellfire), but I have never tried those. Mostly because I could not find a GZG group large enough.

Hope that helps.

I would like to see a little more thought put into these kinds of games that would reflect just how difficult it would be to do a planetary assault, which I think would be challenging for all involved. First, starships really don't want to fight near planets if at all possible(i.e., orbital mechanics). Second, orbital bombardment would be difficult unless you're orbital path is along the equator of the planet as trying to stay over a certain area outside of that zone would suck up all the fuel in your ship! You could probably provide fire support for only a minute or two every few hours. Third, to land heavy forces you would need to seize whatever kind of starport/landing facilities are on the planet, so that would be the number one priority. Given those parameters it would be interesting to see what players could come up with.

Well 40K isn't a very sci-fi game at all, nor, do I think, is it meant to be. It is way more of a fantasy game in space.

As such it seems much more like a fantasy game than a sci-fi one. I think it is pretty good for that, but I don't look to it for sci-fi. There are more sci-fi things in it here and there, like the Tau, of course. But there are also elves, magic and swords.

As others have said, 6mm has a good bit of this stuff. I'd take a look at Future War Commander.

link

Note that it certainly does not have to be played in 6mm.

Battletech has long had a fairly detailed set(s) of rules dealing with planetary invasion. These recently got updated in the new Strategic Operations book I believe. Should fit the bill pretty well.

-Will

if you can handle 'Epic' scale (6mm), the current free rules
for Epic 40K as well as the older sets handle this quite well.. (well.. not the planetary batteries vs spaceships).

But it does have off-planet bombardment and semi-random dropzones (and consolidation problems for the attacker)

It's especially if you like Tyranids..(hehehe)

Yep, G/W Epic, DRM Sow among others handles it well …

One aspect of sci fi that I'd really love to see done on the tabletop would be a planetary assault, complete with starships and surface batteries duking it out while the PBI tried to secure a foothold.

Which is still just WWII air/naval assets duking it out while the airborne and amphibious assault PBI try to secure a foothold. ;)

And yes, I love planetary assault scenarios and starship boarding actions, too. Yaarr!

As already stated, the new Battletech/Battleforce rules address this scenario.

link

Guiscard beat me to it, but I was also going to suggest FT/DS or SG. However, while I think the FT rules are very elegant, I find the ground rules pretty plodding.

had an idea a few years ago about using Full THrust, Dirtside, and Stargrunt in a combined game. I figured I would use the Full thrust rules to initiate the planetary landing then add Dirtside on another table for the ground forces assulting an objective then once troops reach the city, add Stargrunt on another small table for some man to man city fighting. Never really got around to working out all the logistics.

We actually did that back in the mid-late 90's at GenCon in Milwaukee. We probably had 10-12 guys running GZG games and had scenarios for a Planetary Invasion using Full Thrust (and "More Thrust" supplement, Dirtside and Stargrunt.

I ran the Dirtside games. Because of the nature of a convention we did not link the results of one game to the next but it was effectively set up so that it could have been run that way. Those 3 games lend themselves quite easily to running that sort of game.

darthfozzywig "Which is still just WWII air/naval assets duking it out while the airborne and amphibious assault PBI try to secure a foothold. ;)"

I disagree completely. It's a matter of two dimensional vs. three dimensional geometry. E.g., in an imaginary "Nazis invade Britain" scenario, the troops can only be landed on the shore. True, some could be airdropped in, but only the very light stuff.

Planetary assaults, OTOH, probably allow troops to be dropped virtually anywhere on the planet, and probably actually would allow greater maneuverability for the attacking forces (who can strike from orbit) rather than the defenders, who are limited to planetary speeds. The whole thing could become very complicated in a way WWII airborne invasions never were.

I disagree completely. It's a matter of two dimensional vs. three dimensional geometry. E.g., in an imaginary "Nazis invade Britain" scenario, the troops can only be landed on the shore. True, some could be airdropped in, but only the very light stuff.

But to turn back the other way, I would say it's a matter of "load" or "mass" over 2 vs 3 dimensions..

For your Nazi's invade Britain in space scenario, the light stuff is para/orbitally dropped in to secure a "beachead" or "airhead" where the heavy armored troops can be landed by heavy tranports and debarked.

Or better, the Battle of Hoth in ESB. The heavy AT-AT's were dropped outside of the Rebel's defensive zone and attacked conventionally overland.

3-d yes, but in many ways the same issues as 2-d.

Now of course, this is just how I picture it. The reality of future warfare and interplanetary assaults is completely unknown, so my assumptions can be easily overturned by a different extrapolation.

I guess I'm saying that it's not that I disagree with you on the facts, I disagree that there are "facts" and it comes down to what your tastes and preferences are.

Way back when, 'Role-Player Independent' magazine published a series of scenarios for Full Thrust and Hellfire (but dirtside would work just as well). The attackers had to fight into the system past defending ships, identify a landing ground and then use interface shuttles to bring the troops down. As I recall, you only had limited lift capacity so had to choose what was most important to drop first (in case the natives came a'calling).

I think I still have it somewhere so could sort out a copy if it would be useful.

The old Star Frontiers game and it's starship Knight Hawks covered all this in painful detail. A planetary surface of a major civilized world will have several planetary laser batteries and an unlimited supply of interceptor missiles. Planetary bombardment would be conducted from orbit in range of the defence lasers and use area effect weapons, which could be shot down. Yeah, Star Frontiers set up a scenario so planetary sieges could not work, which didn't make us happy.

So we played Battletech which had a very simplistic way of having the fight in orbit turn into the taking land and holding it. But at least we were able to play out the whole battle that way.

I think Heavy Gear has some rules for this as well. It's not covered in the Blitz rules because the landships of Terra Nova don't have stats for Blitz. I've seen stats for the landships for the original miniatures game, and knowing some of the landships were equipped with heavy long range missiles for the purpose of shooting at targets in orbit. I don't know of any one that's played a HG game of the War of the Alliance were CEF ships would pass through Terra Nova's orbit and drop off supplies or take on wounded while avoiding planetary missile fire, all the while trying to spot the landships to retaliate from both orbit and with troops on the ground.

There was an old GDW game called "Invasion Earth" set in the Traveller universe. The imperium was invading Sol / Terra.

The imperial player has to enter the Terran system with his fleet and fight his way into close orbit around earth. He has to juggle between planetary bommbardment and protecting his troop transports and supply ships. Once he is in close orbit he can drop light troops to the surface. Heavy equipment had to be off loaded at a starport.

The Sol player set up his limited fleet resources and had the option to hide them through out the solar system. He could engage in hit and run tactics or opt for a pitched battle with the imperial fleet he was destined to lose. On the ground he had defense baterries that could engage targets in close orbit. Ground forces that ranged from elite mechanized forces to shabby milita infantry. There was partisan warfare.

Granted it was a board game and the scale was division or corp. The game could be used as a back drop for a campaign or reference material and adapt it to your chosen miniature game.

A damn good game and I regret selling my copy.

Not to play a brass instrument I already own, but I wrote an article for the SFSFW journal RAGNAROK about a planetary assualt on a small facility, in which capturing the facility intact for UN inspection was a priority, and the forces attacking were modified from what the palyer was supplied with by a small FT battle, in which the assault carriers could have lost capacity from damage. It used the DS2 rules, FT 1st edition, and the Brigade Models lines of both vehicles and ships . . . Might be up on the website, under the title "In The Garden Of Allah".

Certainly the idea could be expanded; But I must say an assualt on a colony with lower population level would be easier to do, in most systems. You would have to figure the defensive infrastructure of the planet, the possibility of landing conventional marine forces for attacks on targets ( Boats, wtercraft and amphibious tech), the need to grab certain assets rapidily ( Starports, centralised power stations, fuel and other neccessary logistics supply facilities, communicatiosn centres, and transport hubs ), the problem of civilians in any of the desired areas, and a number of other problems.

A planetary invasion would certainly generate many scenarios for minor games as well . . . Must get the write-up done of my own scenario of a dropship run into a container seaport to grab chemicals required by mercenaries for chemical warfare force multipliers ( The old term for WMDs :) ).

And I would say that either an FT/DS2/SG2 combo or an E:A/BFG/W40K combo would also work quite well, possibly even adding IAero into the mix there . . . Which would be really complex, but accurate . . . :D

Or better, the Battle of Hoth in ESB. The heavy AT-AT's were dropped outside of the Rebel's defensive zone and attacked conventionally overland.

That was because the Rebels had a theatre shield up, preventing dropships getting in close. Compare that to the Republic assault on Geonosis or Utapau in the prequel movies; troops debarking directly from starships into combat – like Lt. Col. Kilgore's air cav, but with 750m-long Hueys. :)

Planetary invasions are… farfetched? Let's say, a prospect of tenuous realism. Seems like it would take an awful lot of troops.

If you can control space above the planet, it should really just surrender to prevent you from asteroid-impacting it into uninhabitability.
-Kle.

Ah, Klebert is quoting indirectly the major form James White's novel "Star Surgeon"; 'Planets cannot be captured, Doctor. They can only be detonated.'

However I will counter with a comment made to the leadership of East-Meg One by one Judge Joseph Lazarus Dredd;'You had the chance to vaporise this city ten times over already – and you haven't done it! No, there's no point in destroying a city when it's more useful to conquer it, is there?'

Defiance: Vital Ground has a standard scenario for any army where one force is in place when another smacks down in an orbital lander. There's your sci-fi drop-troop scenario.

Orbital barrage is technically and realistically beyond the scope of 28mm skirmish, but throw in DVG's off-board artillery (called "airstrikes"), an anywhere-on-the-table SIX INCH template… yeah, that works, and it's already a part of the game.

Work one army up with high-mobility vehicles and take lots of APCs, there's your strike force, work the other up with big, slow tanks with long range weapons, there's your ack-ack. THAT works, and it's already part of the game. It also lets you play out the ongoing conflict (again with the standard scenarios) as the invasion unfolds.

mj12games.com/defiance

I agree Walrus … If you toast the whole planet it's no good to anyone. And to capture a planet is basically like capturing a nation or continent … You don't occupy the whole thing, but only key and decisive locations/areas. After nullifying their armed forces of course …

Hmm, I was under the apparently mistaken impression there is an expansion (or something) somewhere that has actual rules for tying the GZG games together into this kind of framework.

Anyway, like smokingwreckage said, Defiance has "out of the box" facilites for the ground combat side (in fact the scenarios on the whole are rather modeled for that type of warfare -- if orbital dropping sounds too far fetched you can imagine it's regular airborne assault of course) if one were to start building a system like this.

There are a variety of space games with rules for troop transports of course, but I can't recall any that handle the phase from orbit to the surface off the top of my head. Must be some tho.

tnjrp, ther eis a framework in the old More Thrust rule book. . . Maybe the FT-based Power Projection might have.

FT has rules that will allow the use of dropships and shuttles in play, and there are rules for entering orbit . . . Not too detailed, but should be something to work upon.

Must be that one I'm recalling then. Glad I wasn't proven completely senile on this subject too (-:)

I agree Walrus … If you toast the whole planet it's no good to anyone.

Exactly. If it's no good to anyone, then it's no good to your enemy. They're down one planet, you've lost nothing.

And to capture a planet is basically like capturing a nation or continent … You don't occupy the whole thing, but only key and decisive locations/areas. After nullifying their armed forces of course …

Right. How many troops do you suppose it'll take to "nullify their armed forces"? Troops you have to move through space to get there… How many people in the armed services on Earth, today? Tens of millions, at least. Let's say you want the traditional three-to-one odds for an invasion… How many planets do you have to strip of their military forces to make up your invasion force? How do you move these people? How long does it take? Not moving them, I mean just getting them aboard the spaceships.

Then, after you win your victory, somehow not taking millions of losses, you just want to "occupy key locations". What, like Europe? How many people is that going to take?

Planetary invasions only make any kind of sense if you figure on something like Heinlein's nuclear-armed battlesuit troops, and even then it's a long stretch.
-Kle.

Take and hold all starports, then manufacturing and food making areas(or something along these lines) – cripples a planet. Don't need as many troops to do it as you think. Stop the ability to get goods onto/off the planet and what's being made/how it's distributed you have control. Not every planet will have that many starports. If ships of a certain size have to use them, you've got control of a lot of things. anyway, it's sci-fi, how the hell/why the hell try and compare it to anything around nowadays?

Seems like the Germans did a pretty good job of "vaporising" Stalingrad, but the Russians kept fighting. Even assuming that the planet has no hope of effectively resisting once an enemy fleet is in orbit, that does not mean the ground commander can do nothing. He can certainly tie up a lot of enemy forces for a long time, and without "neutralizing" them, the planet may be held, but will never be useful.

Seems like Alien Surfer had the same idea, and got it in a bit before me. Oh well, guess I'm in good company.

This sounds like a fun campaign to me: The first few games are planetary assault where the attacker attempts to take and hold space around the planet while locking down key locations on the planet. From there, the attacker has limited forces to police the planet, while the local governments organize a planet level resistance.

Of course the local governments all have their own agenda and will work to make sure they have the upper hand over their neighbors once the invaders are removed from their soil. And the invaders can always make alliances of their own with planet side groups in an attempt to strengthen their own position (alliances they break whenever they stop being useful).

I like this.

Klebert, a fgood point, and one discussed by Larry Niven in one of the Draco Tavern tales; The Chirpsithra, the race who parctically run the galaxy ( According to them ; ) ), once had their worlds invaded by another race that also required tidally-locked planets around red dwarf stars. Fortunately, after the 'Chirps' forced the aliens to capitualte a few times, they discovered that there was a difference between the planets the two species desired, so they came to a mutual agreement.

How did the Chirpsithra do it? Simply, they have different words for the possessive article in each case. For example when a 'Chirp' says "My leg", "My wallet" and "My home" she* uses a different word each time for 'my'. So, they simply atarted to abandond worlds approached by their opponent and on the way out of the system, destabilised the nearest Oort cloud or asteroid belt equivalent to bombard the planet into rubble. Like deafeating a burglar by leaving the house and setting it ablaze with them in it.

Leaving aside alien thinking for a moment, remember that not every colonised planet will have a population as large as Earth's now or even in the recent past which seems to be klebert's take on the matter; It may be concievable that the capture of a planet may be as simple as taking a few major inhabited areas and waiting for the locals to capitulate as in a small country. Yes, this can lead to protracted guerrilla wars and that is an interesting idea . . . . however, look at Roman occupation of countries; Absorption of the population by the conquerering forces can happen in a long period of time, especially if there is n advantage to the locals to becoming citizens or for their children to become citizens. . .

As for food production, H. Beam Piper pointed out how easy it was to control planets whose fauna and flora were only partially compatible or totally incompatible to human nutrition; His commanders often sweated when facing worlds with carnoculture and hydroponic food reliance, not because they were hard to capture ( Denial of supplies to the enemy was so easy ) but the possibility of stretched supplies was the danger. There are amny other situations that might arise on colony worlds that might make them vulnerable to invasion.

And to round this out, what about limited invasion? Suppose the colonists have only heavily populated one or two continents on a planet and left the rest sparsely peopled . . . A foreign group might well land a beachhead force in the open areas and make a claim to hold that continent for themselves, which would make for soem interesting wrangle sin the UN or equivalent.

Final word from me is a restatement of The Stainless Steel Rat's comment son Interplanetary warfare; It seems a complicated and impossibly difficult process, but if human history teaches us anything it is that impossibility has never stood in the way of certain men.

I think the feasibility of a planetary invasion depends on the size of the population of the planet. In the GZGverse, amnkind has onl have star travel for c.100 years, so even major planets won't have that high a population, only(!) a few million, so it is comparable to conquering a country (a very big country with a low population density. In 40K, where populations run into the trillions on major system, then yes it is getting jsut a bit silly.

Planetary assault? Do you mean like the book Starship Troopers, or the movie, or more like the Roughnecks CG-animation?

If you're talking the book MI assault, that's really a skirmish with big guns, where each individual on the attacking side drops semi-randomly. This can be simulated in several different games, even Flames of War.

The movie MI assault on Klendathu is closer to D-Day, and I'd want to play it no bigger than 15mm.

The Roughnecks combat drops are probably closest to what you want (or the Marine insertion in Aliens), and even then it's a basic air-assault insertion or closer to the Airborne rules from Flames of War.

there is a gurps traveller book that explores the concept of nexus warfare to which others here have alluded. If the planet is colonial in nature and not heavily populated, then control of transportation, food, and power sources and transmission venues or hubs (or nexus) would serve as a force multiplier for the invading power. The oppostion would likely mount efforts to free those sources, but that allows the invading power to pick the location of the fights and act as a defender after a secured planethead has been established at those nexus points.

Most games dont deal with enough troops to really represent this. Dirtside is fun and all, but dropping 30 tanks on a planet isn't going to impress a population of billions.

I agree with alot of what was said here … However Klebert, your questions are probably what any capable commander ask or has to deal with … Whether invading a nation, continent or Planet … I think your missing the point … In a far future conflict, these problems would be no different then today's, only on a far larger, hi-tech scale. And your question about how many troops it would take to occupy Europe … The Nazis controlled most of Western Europe by 1942 … I'm not sure of the total number of troops off the top of my head, but obviously it was "do able" … Look how much of the PTO the IJF controlled by '42. The Allies in WWII on D-Day at Normany landed with about 180,000 troops, IIRC … Or how much of Europe & Asia did Alexander control. Or the Roman Empire. To control a region you don't have to have a trooper on every yard of the area. And the logistics of moving and supporting a deployed force … based on my experience in the US Army Infantry ('79-'90) and study of history … it is "do-able" …

"Let's say you want the traditional three-to-one odds for an invasion… How many planets do you have to strip of their military forces to make up your invasion force? How do you move these people? How long does it take? Not moving them, I mean just getting them aboard the spaceships".

Actually, the 3:1 superiority is only against local forces, and if using highly mobile, or very well trained troops against less mobile or less well trained ones, the ratio can drop off considerably, e.g. the British troops in the Falklands were outnumbered in some cases, but still beat the Argentines, by using maneuver tactics to beat them.

Granted, a world may have a lot of people, and/or a large military, but you only need to defeat the ones near your landing areas, and keep the others tied down to prevent them from moving against your troops on the ground.

Obviously, taking a world may be very complex, but I imagine a spacefaring society that can build warships, and troop transports should be able to do it.

Depending upon the planet's need for outside assistance, they may be more or less susceptible to blockades, planetary bombardments, and assaults.

Interesting discussion.

Time to dust off the FT and MT rules, and have at it again.

I like to have a considerable force of planetary, or moon-based spacefighters, missile boats, and other non-FTL vessels for the defense of my solar systems. Makes for great fun against large, capital vessels, escorts, and cargo vessels/landing ships. A large System Defense Monitor or two, can be very useful as well.

The trick in planetary invasions is landing far enough away from the enemy to prevent having your forces decimated during the drop from space to the surface, yet close enough to come to grips with those troops you need to destroy quickly.

Doesn't do much good to land on the far side of the planet, or a continent away, unless you have the capability to move quickly, in order to seize your strategic targets before the enemy can set up an adequate defense.

Of course, you don't want to waste a lot of time, or fuel, getting to the target either, since squandering either is wasteful.

And very good points Ace … 3 to 1 is local superiority (5-1 if heavily entrenched/fortified) … like a Company attacking a Platoon … How do you move the troops ? How long does it take to load the Spaceships ? (How long did it take to get 180,000 troops loaded up on ship & aircraft for Normandy ?) Those are the same considerations any Bn or Bde staff has to answer today … I know because I did it … But we were moving troops to airfields, railheads and ports and into aircraft, trains or ships … Not Spacecraft … And I'm sure Div, Corps and Army staffs have the same considerations …. Only on a(much)larger scale …

"How many troops do you suppose it'll take to "nullify their armed forces"

A good question, if Iraq is any example I would say one armor brigade. I guess it depends on tech level of the opponents and the nature of the occupation afterwords.

That question is another one the S-2/G-2 would have to answer … What do we see on recon pics ? Do we have HUMINT assets on the ground ? What do they say ? What do other intell assets(allies, EPWs, etc.?) have to tell us ? The 4th AR Div is at Bagram Air Base. The 3rd ID is stationed in and around Kabul and the 4th ID is operating near Herat. There is a Motorized Bde at Khalli Jengi. O.K. S-2/S-3 go to work. Gee, sounds like a StaffEX situation we had to work out at Combined Arms School …

Well, science fiction has certainly imagined plenty of luvverly stuff to kill ecosystems or even whole planets with. And it is certainly true that if you do that it's 1-0 for the home team as per the number of habitable (and possibly in any way utlizable) worlds. But still it'll mean you've squandered the resources of an entire planet if you "nuke it" from orbit -- talk about "salting the soil" or rather doing the more modern version of spreading plutonium dust on it. Few wars over the course of history, I think, have been so total.

Assuming there are reasons to colonise planets, there will be reasons to conquer them. If we assume planetary colonialism of some sort then planetary invasions make sense.

That given, saying "planetary invasion" probably makes as much sense as calling D-Day a "continental invasion". You don't invade the entire continent, nor an entire planet (except if perhaps you have the resources for such a novel gambit). You seize specific sites- cities certainly.

Consider invading Earth: most of the surface is effectively uninhabited. 2/3rds is ocean, then the deserts and arctic areas, you would not bother with the agricultural lands either. In point of fact it would be about equivalent to any other invasion, and not even necessarily on a larger scale.

anyway, it's sci-fi, how the hell/why the hell try and compare it to anything around nowadays?

Because otherwise, it's fantasy, and not sci-fi?

Seems like the Germans did a pretty good job of "vaporising" Stalingrad, but the Russians kept fighting.

Sure, but Stalingrad was definitely not producing anything for the war effort.

I'm also not talking about a Stalingrad-equivalent, with Hitler's pathetic strategic-destruction capabilities. I'm talking Hiroshima and Nagasaki, which both ceased resistance pretty dang well.

Smash the planet, then leave. Don't smash the planet, and then drop 40 million troops to try to hunt down the survivors for ten years…

I think the feasibility of a planetary invasion depends on the size of the population of the planet.

Actually, the 3:1 superiority is only against local forces, and if using highly mobile, or very well trained troops against less mobile or less well trained ones, the ratio can drop off considerably,

Sure, but in these cases there's absolutely no reason for the defenders to fight, because they're going to be trivially overwhelmed. Many of them will fight anyway, but 300-1 odds, or vast disparities in fighting ability usually make for poor games.

Look, I'm not saying that it would be impossible to invade a (equivalent population peer-competitor) planet, just that it would be incredibly difficult and require enormous resources.

Kill a couple planets, and the rest will probably surrender after you win the space battle. Then you can keep them with limited garrisons, and some starship support. Worked pretty well for Ghengis Kan and the Chinese, with cities. Rational planets would surrender even w/o previous planet-killings, since planets are eggshells to interstellar civilization levels of technology. They give their parole, everything goes better with less death and suffering.
-Kle.

From a practical point of view, if your approach is the Klebert planet-smasher one, you'd better hope that your starfleet has the ability to refuel and replenish elsewhere in the system or has the ability to "leave" without that.

From a strategic point of view, the planet-smasher approach would seem to require unilateral possession of such weapons (Hiroshima), otherwise one would be inviting retaliatory planet-smashing operations against your own systems. MAD anyone?

"Sure, but Stalingrad was definitely not producing anything for the war effort."

The Red October factory was still turning out T-34s WHILE IT WAS UNDER ATTACK. I'm sure other factories in Stalingrad were doing the same.