The example I presented covers a small-to-medium planetary invasion in the midst of a larger, sector-scale conflict (the Achilus Crusade). There are significant Tau forces present, and the world is Earth-like and industrialised and thus relatively valuable. The Astartes and Adeptus Titanicus presence is disproportionately large - those things have a particularly large presence in the Crusade, so their presence is justified in context - but the ground forces are those I deemed necessary to not merely conquer a world (swoop in, cut off the head, call for surrender), but eliminate a dispersed, mobile enemy invasion force across multiple continents and discrete regions. As my example describes, the forces are spread across numerous planetary theatres, which would all be fighting their own distinct battles with relative autonomy. That is, I worked on the premise of a World War - a conflict raging across an entire planet. Planets are, afterall, very large, and the typical flawed sci-fi approach of "each world is more or less just one town or city" doesn't sit well with me.

Your numbers and approach work for me, NO-1. In an earlier post I guesstimated loosely that you'd need about 15-20 million guardsmen per billion of the local population to conquer a world, assuming the population (and enemy) were drawn from were an equiv-tech level human society. You've estimated 70 million Guardsmen for an "Earth like" (circa 7 billion population) world, with significant higher-tech Xenos opposition; your Guard force is therefore a little small according my hastily drawn formula, but the leveller here as you say is the Astartes, fleet and Titan support. Note I'm not saying my formula is correct! It was simply an extrapolation of the numbers in a WWII scale conflict, an approach which logically has many many holes in it...

And collateral damage is effectively inevitable considering the terrible weapons unleashed in the average campaign, both by the Imperium as well as its enemies.

Really, it comes down to either adopting or ignoring these parts of the studio material, such as the quote about orbital bombardment accompanying every invasion I posted previously, or the many times we read about all sorts of damage to local infrastructure in some piece of background. So the way I see it, the puzzle pieces fall into place if you simply take everything "as is". If however you dismiss the Imperium's ability and willingness to inflict massive damage in the course of its battles, then of course you must ramp up the number of conventional forces you wish to send against the defender.

And as previously mentioned, if there is something valuable you want to have saved, you better call in the Space Marines. They are the scalpel, the Imperial Guard is the hammer. If you bring down the hammer, you generally should not expect to have much left standing at the end.

Here's the thing - if you're trying to sell miniatures (as in codices and wargame rulebooks) or focus on individual protagonists (novels), then you scale down the battles or otherwise treat the wider conflict as a backdrop - for a wargame, you want to present battles of a sort players can aspire to play, for a novel, you need to focus on the characters, rather than the broader events around them. It's a matter of focus, not of absolute truth.

That sounds like an unfair downplay towards Games Workshop's original material. If we're talking about entire regiments of thousands of troops, then this is a focus not applicable to either a wargame or a novel. Or a roleplaying game, for that matter.

The only focus that could be applied here is world-building, and this is something you do in any of these media.

"Absolute truth" is something we will never have in this IP, anyways, simply due to how it is managed.

Particularly when official material has often frequently lacked internal consistency on the matter of scale (Re: the Stormtrooper debate - the 2nd Edition Imperial Guard codex explained on one page that the Stormtrooper Regiment was a particularly large regiment at 10,000 souls, yet other parts of the book said that each regiment consisted of all the men recruited to the Imperial Guard from a single world at a single muster... which when you imagine Hive Worlds, makes the idea of 10,000 men being a 'large' regiment to be frankly laughable

Well ... only if you assume that Hive Worlds make up a large enough percentage of overall Imperial worlds as to skew the average in this way. The BFG rules for subsector creation state that these are in the minority, compared to agri-, mining- and other less populated worlds.

Also, if you've read the 2E Guard 'dex, you know that the overall number of forces available for recruitment depend entirely on the size of the local governor's PDF. Even on a Hive World, a tithed regiment may only be 5,000 strong if, for some reason, the local governor's army consists only of 50,000 troops.

Again looking at the Third War for Armageddon, we can see that this planet's PDF consists of 25 regiments of the Steel Legion. In addition, over a hundred regiments of Hive Militia have been armed and raised from the local civilian populace to aid in the defence of their homes, but these are impromptu forces that were not considered "titheable" before - unless a governor would cheat and induct them into the PDF only to ship them off-world, which probably explains certain practices such as regiments raised from criminals.

But there is also the Munitorum's practice of determining the size of a regiment based on the quality of its troops. This is something that actually only came into being with 3rd Edition and so may possibly retcon parts of the 2E Codex (though both approaches are not necessarily mutually exclusive), but it suggests that regiments from a Hive World - which probably has access to advanced weaponry, and perhaps experienced warriors (such as Necromunda recruiting from the underhive gangs) - may be smaller in size than regiments of inexperienced conscripts with no prior experience (like a bunch of malnourished fungi farmers from Valhalla), simply to ensure that the "battle value" of each Imperial Guard regiment is roughly equivalent. Perhaps Hive Worlds are thus tithed more often in small amounts, rather than once for millions of men and women? Depending on their location and the availability of naval transports, of course. A need is always there...

I think that, for RPG's, each group really should work itself out and decide what seems to function best for them. It's a terrible answer, when you could possibly have real numbers to work with, but it's also the best answer because of the nature of the figures in the setting.

However, it's fun to discuss.

That much is true. I used to be much more, um, zealous back when I still believed in the lie that the setting actually had a solid canon, and I was unfairly antagonistic and arrogant towards N0-1_H3r3 as a result. Operating from the position that it's all just about interpretations and personal preferences certainly makes it easier for all of us.

At least somewhat.

The Achilus crusade has 30 billion troops after considerable reinforcement and that is a full fledged attempt to reconquer a sector

May I ask where that number is from? I am not that familiar with the content of Deathwatch and the force organization I found on the Lexicaum seems quite odd if compared to 30 billion.

Also, what billion are you referring to?

1.000.000.000.000 in long scales or 1.000.000.000 in short scales?

In then End I still stick to the low number approach for every battle in the Lore seems to be focused around some very specific area. As mentioned before several times the infrastructure of the WH40k world is mostly centralized together with its population and the technology allows even smaller forces to carry insane firepower. Also with the integration of support units like Titans your scaling is utterly flawed for these compare to entire armys themself and had to be subtracted from your up scaled manpower. One Titan can win an entire war and the presence of a legion can make the enemy surrender before even one shot has been fired. Also the IG is heavily dependent on ordnance and Armour that can reach a ludicrous efficiency in IG arsenals. The Leman Russ is nearly as heavily armored as the Land Raider, a friggin fortress on chains dedicated to drive troops through the thickest fire right into the heart of battle. In a WW2 scenario that would be a King Tiger with the idiot proof and always available design of a Sherman with even more weapons attached to it. And we have not even spoken about Super-Heavies that have to be a crazy force multiplier.

And that is what makes the numbers okay in my interpretation of the fluff. The IG owns a lot of such force multipliers to make up for their numbers. Also the IG is more or less always at front duty where else your WW2 examples always include the troops that guard the home territory or are far away from any combat at all.

Page 28 of the DW 'The Achilles Assault'. It also specifically mentions that less than 20 percent of guardsmen of the IG are serving in the combat arms. The rest is serving in 'combat support, internal security, occupation, reserve, lines of communication and rear echelon roles.

It's not just about moving a percentage of the population of the Wh40k setting around. It is doing so with a highly limited amount of space ships, and doing so for countless war zones all across the Imperium simultaneously. You have entire fleets disappear into the Empyrean for months or years at a time, fleets which can only be maintained or rebuilt at a shockingly small amount of places due to the technological recess. This is why interstellar transportation in the setting is supposed to be rare (what I consider a critical element of the overall atmosphere as it sets the style of space travel apart from "everyday business" as in, say, Star Wars or a myriad of other IPs), and though you may raise your armies of Guardsmen on just about any feral world, there's just no way to actually put them where they are needed. This is why worlds can go for decades or centuries without having to send troops even just once - though, at the same time, planets closer to an important war zone may see their tithes increased.

It's all a matter of degrees. If you have a total population in the order of a third of a quintillion, then the interplanetary and interstellar infrastructure must be commensurately large to allow such a population to exist. The Imperium is capable of existing as a civilisation of that size over such a vast area is because of comparatively stable and efficient interstellar travel and communication.

Space travel is rare... in the sense that the overwhelming majority of people in the Imperium will never leave their homeworld, and travel much beyond the short, relatively stable routes between nearby worlds (voyages not measured in years; weeks is a better estimate, months at most) is virtually unheard of outside of military necessity and the likes of Rogue Traders. Still, the sheer, mind-boggling quantities of materials and materiel that need to move around the Imperium requires that infrastructure exists to move those things. Bulk haulers capable of transporting hundreds of millions of tonnes of goods (or a comparable quantity of soldiers) will be a frequent sight in the high orbit of hub worlds (those in the centre of a local region's structure). Even isolated, primitive worlds exist because they serve some purpose to the Imperium (a world that cannot contribute to the Imperium isn't worth sustaining with external resources, an idea presented in the short story Mortal Fuel in the anthology Planetkill ), meaning that such worlds will see a handful of ships a generation at least - ships to gather the tithes, Blackships, occasional Navy patrols to check for threats, etc.

That doesn't mean it's efficient. The Administratum exists to manage and maintain the largest civilisation in human history, and human error causes problems detailed in many places... but it functions well enough that the Imperium hasn't collapsed. Just as importantly, the Imperium has never left its war footing, and is thus built with a mind to maintaining a powerful military on a vast scale. That is, in fact, the sole purpose of the Departmento Munitorum - to strive to ensure that military resources are where they're needed.

Within the context of a Crusade, moving a few tens of millions of troops to a world on the front lines is entirely feasible on a fairly routine basis - afterall, an active Crusade represents a local concentration of not only force, but of the logistical infrastructure needed to support and deploy that force. It also represents an environment where Adeptus Astartes and Adeptus Titanicus forces are likely to be in greater local supply than they ordinarily would be. Moving that sort of force to a completely new warzone isn't impossible, but requires greater effort - you need to spend time moving things around that would already be on-hand during an established conflict.

I don't disregard canon sources - where possible, I try and incorporate as many of them as possible, especially if the same concept appears in multiple sources (which is generally how ideas tend to propagate through the setting - writers seeing ideas they like and expanding them with each passing iteration). But I see "mindboggling scale" as being something that compliments the canon, a few ill-chosen numbers aside, rather than something contrary to it - it's something that I feel works well with the tone and themes and implications of the setting, even if it runs roughshod over a few specific details (indeed, my time spent contributing to the RPGs has taught me that specific details and concrete numbers are generally bad things to add to 40k; they're intrude rather than inspiring).

Oh, and "calling in the Space Marines" is far, far easier said than done. One Space Marine per planet, approximately speaking, combined with their practical autonomy from the Imperium, means that the best you can do is petition them for aid and hope they respond. It's why the Imperial Guard has their own special forces in a variety of forms, with the Storm Trooper Regiment at the very top (where I still prefer to take the "unusually large regiment" statement as truth, and ignore the specific "10,000 men" detail - and I like to imagine that Lord-Colonel of the Storm Trooper Regiment is a largely ceremonial/political role, serving as an advisor to the Lord Commander Militant of the Imperial Guard).

I'm well-versed in the various ways and complications of raising regiments of Imperial Guard, and the inconsistent definition of them - I had to do a fair amount of research for the Regiment Creation chapter of Only War, and this was part of it. To quote myself:

What this all boils down to is the regiment. The regiment is the building block of the Imperial Guard, and the nature of each regiment defines how it is to fight, how it is to be equipped, and the manner in which it is best employed. Regiments are raised either as part of the tithe that all worlds contribute to the Imperium, or as necessary from worlds within a particular distance of a newly-opened warzone. It is

a rare world in the Imperium that has not raised at least one regiment of Imperial Guard, with the overwhelming majority of those being the tithe-exempt forge worlds and the home worlds of the Adeptus Astartes, both of which produce their own particular fighting forces.

Though regarded as such by many within the Departmento Munitorum, a regiment is not a uniform mass of warriors, equal in might and utility to every other regiment. On the contrary, regiments vary immensely in size, structure, and purpose, from small, deadly, armoured regiments, to bewilderingly large regiments of siege infantry. In truth, the regiment is a difficult thing to define, but some might classify it thusly: a regiment is the operational unit of the Imperial Guard, a discrete formation of Imperial Guardsmen, all trained and equipped to operate in a single way, and all drawn from a single world. All other factors are subject to local variation and prevailing logistical doctrine—at times, all the fighting men taken from a single world at a single time have been classified as a single regiment, creating units of millions of

men, while other periods and places have attempted to define a set number of warriors or an arbitrarily calculated fighting strength to determine a regiment.

Long story short - there's no single definition of Regiment. The number of contradictory sources on the subject can basically be rationalised into local variations and perpetual changes in Departmento Munitorum doctrine. The fact that many of the Hive Worlds we know about tend to give part of their tithe in regiments (rather than purely when required by nearby conflicts) suggests that they do tithe more frequently and produce proportionally more regiments than other kinds of worlds (barring fortress worlds, death worlds and other planets whose primary resource is tough, dangerous people). Still, it doesn't resolve the fact that the 2nd edition codex test is contradictory - rather, it shows that taking multiple sources into account in a creative manner provides the best way to resolve the issue.

At some point this entire discussion becomes pointless beyond amusement and overal clarification for GM's IMO.

After all, Only War is about players in a squad. The promise of playing characters with a higher level of authority has (so far) not been fulfilled.

And a simple (or even a not so simple) grunt would have little knowledge of actual numbers of troops. Often, his world is not bigger than his own regiment, the opposing force and perhaps the adjacent regiments. Therefore it should suffice for the GM to mention that the players are part of a major invasion with many millions of troops and let it go at that or that the invasion is a low key or shoe-string effort and only one or a few regiments have landed and there are never enough troops to go around.

You've got a point, though a lot of players like to know details even just out of character as a means of immersing them in the game's world. Kind of like a second perspective where the player is granted the insight of an omniscient observer, as if they were watching a movie. The books supply a lot of background that doesn't directly affect the player characters (with the ignorance of the average citizen in 40k, some might argue a single page of fluff might suffice!), but it's still critical to evoke an attachment to the setting.

But ... the debate is pointless nonetheless, simply because at the end we've all read and adopted or dismissed different sources and interpret their contents differently. If, after 2-3 pages of debate neither side managed to convince the other of their own subjective perspective, then perhaps it is time to agree to disagree.

Within a RPG group, I would simply solve such issues either via majority vote or by attempting to circumvent their appearance. I have the great fortune that my current group shares most of my interpretation of the setting as well as a preference for the very same sources, and I hope for everyone here they have similar luck. Common ground is important.