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So in Book 9, "His last command" it states that the 81-1 Belladons have very few actual commissars, only 5. They are a regiment correct? That puts the minimum at 5. I think Rain's book has 1 per company, which would be 8-10+ per regiment, if you count the support battalions (food, transport, repair, processing, etc). This also doesn't take into account the Commisariate having their own command unit, likely with junior commissars, (Still count) and other Schola adepts, likely a commanding commissar.

I would put it at 10-15 sash wearing commissars per Regiment, maybe the same of trainees, juniors, and a high ranking command person.

FezzikDaBullgryn wrote:
So in Book 9, "His last command" it states that the 81-1 Belladons have very few actual commissars, only 5. They are a regiment correct? That puts the minimum at 5. I think Rain's book has 1 per company, which would be 8-10+ per regiment, if you count the support battalions (food, transport, repair, processing, etc). This also doesn't take into account the Commisariate having their own command unit, likely with junior commissars, (Still count) and other Schola adepts, likely a commanding commissar.

I would put it at 10-15 sash wearing commissars per Regiment, maybe the same of trainees, juniors, and a high ranking command person.

Are you giving that number as an average? It is probably a reasonable average estimate. We know that regiments can have just one assigned (and none whilst waiting for replacements if the commissars die), and there is at least one known example of a regiment with 18 commissars to just three understrength infantry companies.

I suspect the upper end is potentially approaching 100+ commissars in a single regiment when extrapolatimg out the numbers from the Cadian 180th to larger regiments. Maybe for the Terrax Guard.

I would actually suppose Cadian regiments to be less needing of commissars. To the point of it being a pointless waste of them. There are no "raw recruits" with morale problems on Cadia. All of them are extremely seasoned vets by, like, age 13? Fluff aside, there are the two cadian books where Minka Lesk's company/platoon (I forget which) is assigned a commissar detachment because their assigned regimental commander is a pompous ass, that feels the cadians lack the fortitude to actually make the assault. I forget the exact details, but the commissars are basically a waste of space for the entire book.

We are forgetting of course the secondary aspect of having commissars in with units. Aside from being "morale boosters" they are also basically Kasarkin-level trained soldiers. They are each extremely skilled, to the point of being special forces. And they carry weapons that most other Guard never see. Incredibly rare stuff like Plasma Pistols and Powerfists. Most Company commanders don't even carry those.

Depends on the size of the regiment. Generally they are in the range of what we'd refer to as a regiment in modern terminology.

The siege of Vraks for instance consisted of 5 Kreig corps and each one generally consisted of around 4 infantry regiments(consisting of around 4000 men each), two of artillery and an armoured/tank regiment. (So very much what you'd consider a division these days).

This is about the same size as the UN intervention in the Korean war(albeit the infantry regiments themselves are double strength) and would be vastly outnumbered by the Chinese army of the same war, them fielding 4 army groups, each consisting of 3 armies that each contained 3 corps. Not something that has gone into history as an incredibly large war. Thought I'd point this out as Vraks was considered a collosal meat grinder in universe. This suggests that imperium may be vastly underpopulated and worlds that truely hold populations in the billions are few and far between.(or perhaps more likely the writer's grasp on numbers has been consistently quite underwhelming and we should be multiplying things by large orders of magnitude.)

Anyway back to comissars: for them to be effective you'd want one at company level of each of the infantry regiments. One per 250 or so guardsmen should be a pretty strong but reasonably disperced pressence. That is around 48 per regiment, we'll half this as companys will be in resurve or on 2nd line duties. Commissars would be pretty wasted away from frontline duties. So by the time we kit out 4 line corps and an assault corp we have around 360 commissars before you get to replacements, cadets in frontline training etc. Someone needs to manage this fairly large group of people and make sure they are getting what they need to do their job, etc so i imagine that job goes to the most experienced/suitable one the lord commissar.
This is of course the biggest deployment of imperial guard forces you can find reliable numbers for. So typical deployments can easily be a fraction of this. 24-72 should be the normal ball park.
That's just how i figure it anyways.

But the idea that the imperium is vastly unpopulated makes a lot of things in universe suddenly make sense. 1000 marines is a substancial force if planetary populations are in the hundreds of thousands. Likewise 2000-4000 guardsmen are also a substancial force and you'd not actually want to give them resources(their own spacecraft and atmosphereic fast moving aircraft) that could lead to them dominating local PDF forces, commandeering the meagre output of a planet and carving their own little realm out in the stars.
Geez, in this context the Chinese army of the Korean war becomes a veritable tyrannid swarm. It'd strip the land of food and quickly overwhelm anything smaller than a substancial imperial army. Hell add the MacArthurian levels of incompetence in the imperial army and well you have whole regiments being cut off and disappearing overnight without so much as a whisper. Something unthinkable at the time(of the korean war) as it would be within the imperial army's administration. It would really fit well into 40k lore however. Even down to the incompetent sector commander repeatedly urging his superiors that the only path to victory in the sector is through use of exterminatus whilst trying to undermine their power.

Cadians have the issue of turning to Chaos due to proximity.

And arguably commissars are just as important away from the front line maintaining discipline when the troops get bored and start mucking about.

Double or triple the numbers to suit the regiment in question. I just worked out a baseline working figure. Probably halve it for Kreigers. They do not need commissars as such and your casualty rate leading frontal assaults would be pretty bad. It'd basically just be a waste of trained professionals to have a 1 per company dispersal to frontline units at that point.

Also comissars are basically extremely motivated and well trained spare officers. So if a company commander goes down, or is found wanting, or really anyone in that chain of command needs to be replaced you essentially have a fanatical and highly trained replacement who will follow their orders out no matter what.


Automatically Appended Next Post:

 Lord Damocles wrote:
Cadians have the issue of turning to Chaos due to proximity.

Proximity may breed resilience. And what would stop commissars stationed on cadia from being influenced?

In the Cadian Blood book, the 88th Mechanized ran without a Commissar for a while, thanks to some manner of loophople that allowed the Cadians to get away, until the local General uses the fact the regiment has a Psyker to overrule that. It's also specified that he assigned a non-Cadian Commissar, which was an insult for the Guardsmen.

In other words they are, much like their homeworld, pretty much recognised by the administration as being able to deal with possible chaos corruption internally. Interesting.

Kreigers i imagine do not have the issue of being corrupted either.

The main POV character, a Captain, was given training in how to handle psyker, as well, I forget if he specifies it is on par with what the Commissar handlers get, however.

Oh of course if you're from Cadia, its going to be an ever present threat with your psychers there. I imagine it'd be something like we saw on Astartes? But less punching and more hacking. Grenades maybe?

Being able to identify when to put a lasbolt through the psyker's head, and more importantly, when not. Things to that effect. The Kasrkins Master Sergeant simply pistol whips the psyker at some point.

Different methods

 OldMate wrote:
Depends on the size of the regiment. Generally they are in the range of what we'd refer to as a regiment in modern terminology.

The siege of Vraks for instance consisted of 5 Kreig corps and each one generally consisted of around 4 infantry regiments(consisting of around 4000 men each), two of artillery and an armoured/tank regiment. (So very much what you'd consider a division these days).

This is about the same size as the UN intervention in the Korean war(albeit the infantry regiments themselves are double strength) and would be vastly outnumbered by the Chinese army of the same war, them fielding 4 army groups, each consisting of 3 armies that each contained 3 corps. Not something that has gone into history as an incredibly large war. Thought I'd point this out as Vraks was considered a collosal meat grinder in universe. This suggests that imperium may be vastly underpopulated and worlds that truely hold populations in the billions are few and far between.(or perhaps more likely the writer's grasp on numbers has been consistently quite underwhelming and we should be multiplying things by large orders of magnitude.)

Anyway back to comissars: for them to be effective you'd want one at company level of each of the infantry regiments. One per 250 or so guardsmen should be a pretty strong but reasonably disperced pressence. That is around 48 per regiment, we'll half this as companys will be in resurve or on 2nd line duties. Commissars would be pretty wasted away from frontline duties. So by the time we kit out 4 line corps and an assault corp we have around 360 commissars before you get to replacements, cadets in frontline training etc. Someone needs to manage this fairly large group of people and make sure they are getting what they need to do their job, etc so i imagine that job goes to the most experienced/suitable one the lord commissar.
This is of course the biggest deployment of imperial guard forces you can find reliable numbers for. So typical deployments can easily be a fraction of this. 24-72 should be the normal ball park.
That's just how i figure it anyways.

But the idea that the imperium is vastly unpopulated makes a lot of things in universe suddenly make sense. 1000 marines is a substancial force if planetary populations are in the hundreds of thousands. Likewise 2000-4000 guardsmen are also a substancial force and you'd not actually want to give them resources(their own spacecraft and atmosphereic fast moving aircraft) that could lead to them dominating local PDF forces, commandeering the meagre output of a planet and carving their own little realm out in the stars.
Geez, in this context the Chinese army of the Korean war becomes a veritable tyrannid swarm. It'd strip the land of food and quickly overwhelm anything smaller than a substancial imperial army. Hell add the MacArthurian levels of incompetence in the imperial army and well you have whole regiments being cut off and disappearing overnight without so much as a whisper. Something unthinkable at the time(of the korean war) as it would be within the imperial army's administration. It would really fit well into 40k lore however. Even down to the incompetent sector commander repeatedly urging his superiors that the only path to victory in the sector is through use of exterminatus whilst trying to undermine their power.

Where do these numbers for DKoK regiment size come from? Imperial Armour volume 5 describes the first siege regiment to land on Vraks as having 200000 men, not 4000. Two orders of magnitude greater. It also describes the first offensive being conducted by three regiments with 500000 soldiers in the assault. One action within this assault describes the 32nd company being decimated- given Krieg infantry companies are approx. 700 soldiers strong, that implies at least 22000 soldiers in that regiment. They were losing 2000 guardsmen a day across the 88th siege army following this.

Imperial Armour volume 7 records the total death toll for Vraks as 14 million guardsmen, which is fairly substantial.

Also, we know the approx. proportion of hive worlds in the Imperium pre-rift. There are about 32000 out of ~1000000 total worlds, so about 3% of worlds have very high populations.

 Bobthehero wrote:
In the Cadian Blood book, the 88th Mechanized ran without a Commissar for a while, thanks to some manner of loophople that allowed the Cadians to get away, until the local General uses the fact the regiment has a Psyker to overrule that. It's also specified that he assigned a non-Cadian Commissar, which was an insult for the Guardsmen.

That sounds a bit counter to normal practice. I thought part of the point was to assign commissars from different places specifically to ensure an independent point of view. If the commissars are coming from the same place as the troops, waaaaay too easy to let laxity creep in

all very well for Catachans just not to like commissars, for example, but I don't think there has ever been an indication that you solve this by providing them with commissars from Catachan.

Sounds like it was a good thing Cadia exploded, before some real heresy set in! [/s]

I'm simply running off the TTP of the US Military here, but a division (Modern term for the older term, Regiment) is made up of Battalions, usually between 6-8. Depending on the type of division. Or if its a +/- unit. Each Battalion consists of between 3-6 companies. Usually 4, not counting the HQ company. Each company is made of 4 platoons, not counting the HQ unit. Each platoon is made up of 4-6 squads, depending on type of platoon and purpose.

Each squad is 2 teams. Each team is 3-6 persons. Not counting vehicles.

That makes a division between 6-8 thousand troops, not counting support units.

If 40k is at all based in modern types of strategic thought, which it certainly isn't, then a single "regiment" would have just under 10k troops.

Again, 40k fluff is wildly off the mark when it comes to the terms they toss around. Like they use "squad" to describe a platoon strength element at times. The Tanith alone have a "Scout" squad that numbers in the 10s of troopers. Their "companies" number in the thousands. Like I said, wildly off the mark.

 Flinty wrote:
That sounds a bit counter to normal practice. I thought part of the point was to assign commissars from different places specifically to ensure an independent point of view. If the commissars are coming from the same place as the troops, waaaaay too easy to let laxity creep in

all very well for Catachans just not to like commissars, for example, but I don't think there has ever been an indication that you solve this by providing them with commissars from Catachan.

Sounds like it was a good thing Cadia exploded, before some real heresy set in! [/s]

TBF there have been quite a few instances of same-world Commissars and Regiments.
The benefits of an independent Commissar are that they don't get overly attached to the troops they might need to execute but then they also can't relate to the soldiers and encourage them in more meaningful or personal ways. A Commissar from the same planet loses that lack of attachment (to some degree) but then gains the benefit of knowing the culture and creed of the troops they lead. They can regale them with victories of their forebears or evoke imagery of home to encourage steadfastness in the face of the enemy, an "If you fall, home falls" sort of deal.
With the Cadians, they don't really like outsiders all that much so having Cadian-born Commissars gets rid of that issue. Combine that with the very militant and strict Cadian culture and the issue of getting attached is reduced.

FezzikDaBullgryn wrote:
I'm simply running off the TTP of the US Military here, but a division (Modern term for the older term, Regiment) is made up of Battalions, usually between 6-8. Depending on the type of division. Or if its a +/- unit. Each Battalion consists of between 3-6 companies. Usually 4, not counting the HQ company. Each company is made of 4 platoons, not counting the HQ unit. Each platoon is made up of 4-6 squads, depending on type of platoon and purpose.

Each squad is 2 teams. Each team is 3-6 persons. Not counting vehicles.

That makes a division between 6-8 thousand troops, not counting support units.

If 40k is at all based in modern types of strategic thought, which it certainly isn't, then a single "regiment" would have just under 10k troops.

Again, 40k fluff is wildly off the mark when it comes to the terms they toss around. Like they use "squad" to describe a platoon strength element at times. The Tanith alone have a "Scout" squad that numbers in the 10s of troopers. Their "companies" number in the thousands. Like I said, wildly off the mark.

Firstly, I think brigade is the equivalent to old US regiments- division is the next level up IIRC.

Whilst Imperial regiments do have a wide variety of organisations and structures, most do follow roughly the same structure of squad < platoon < company < regiment with roughly analogous sizes for the first two, generally fairly consistent for companies, and wildly variable for regimental sizes.

Generally, I think you will find a better analogy to this in the British army system, particularly from the WWI and WWII era, than the US army organisation. This makes sense, being a lore developed by brits

Within the British system, regiments are an administrative and ceremonial organisation, not a combat one. They have a minimum size of one battalion, and no upper limit of size, and are formed of broadly the same kind of unit (armoured, infantry, artillery etc). The largest British regiment I am aware of (by number of battalions) was the Royal Tank Regiment, which had 24 in WWII. The battalions are the actual combat units, and the battalions are split out of the regiment and formed into 3-battalion (plus support elements) brigades for deployment, which are generally combined-arms units. Brigades are analogous to the larger Imperial Guard battlegroups.

Battalions are much more standardised, and are divided into companies and platoons in a similar way to typical IG equivalents. The main difference is they are smaller (a real British WWII platoon typically has 3 infantry squads, an IG up to 5, a WWI British platoon has 4 infantry squads, the DKoK up to 6).

Battalions are not mentioned much in lore, but I strongly suspect larger Guard regiments (like Valhallans) are frequently divided into battalions for practical purposes- at least to be equivalent to the "standard" regimental size of 3000-8000 that seems to be what most planets muster their forces at. We know the Gudrun Rifles use battalions. My personal headcanon is that Guard battalions are typically 6 companies, because this matches the company-colour method of organisation: a battalion would contain red, green, blue, white, yellow, and black company. The next battalion reuses the same colours, and that prevents a large regiment from needing more and more obscure colours to differentiate companies after the first 6. Conveniently, 6 full Imperial Guard companies is approx. 2000-3000 troopers. Therefore most IG regiments would have 1-4 battalions.

No one wants to be in Beige company… Oystershell company is mainly a ceremonial unit

Behold the power and might of a typical cadian regiment. It's just scraping by at the bottom end of a battalion. Cadian regiments are apparently battalion strength.https://wh40k.lexicanum.com/wiki/Imperial_Guard_Regiment#/media/File%3ACadianRegimentsArt.jpg

These guys would definitely be turned into hamburgers by a company of space marines. Although the idea of them seizing or defending a planet bigger than a red dwarf planetoid is pretty laughable.

My head cannon is either you have "regiments" with straight out 10-20 million soldiers. Of course this would mean that every regiment is some mix of infantry tanks, artillery and support. This would give a regiment somewhere near the frontage needed to hold a continent which would be vital in planetary warfare. It would also make sense as part of the planetary tithe. You are asking them to give up a considerable percentage of their prime working age manpower.

In ww2 there was about 70 million combatants, this is obviously including naval and airforce personnel.BUT the war was condensed to only a limited number of theatres. So the fighting strength of 3 "regiments" a pretty standard large war by 40k standards is in the same ball park as ww2 but before we figure in aerial assets and logistics and support; this puts us neatly into the epic scale of conflict they aspire to in 40k(and in many cases quite amusingly fail when numbers are comically small in what is meant to be a global war(i have a vivid imagination and can easily imagine tens or hundreds of thousands of troops strung out on a frontage of hundreds or thousands of kilometres, of tiny elements of armies clashing in squad level skirmishes along a thousand mile front because that is how thin they are forced to deploy). Or on the other hand that there is literally thousands of regiments in any conflict.

The issue with scaling guard up to deal with a planetary war is that Astates start to look really frickin irrelevant. Dispatched 100 space marines to reinforce a planet? In a war where there is 80 million troops per side? They had best be everywhere at once and individually have the striking power of an ICBM.

Hence why i put forwards the 'vastly unpopulated imperium' theory before. It is the inly way to make a space marine chapter strength deployment relevant in a global war(or a regiment having a single baneblade, its contending with dozens of enemy russes then, not tens of thousands of them); as 99% of depictions of them have space marines performing a shock role on the front lines. And it does not matter how good they are the disparity in firepower will quickly become apparent. And if the enemy hold the battlefield they cannot recover the geneseed.

In the first Gaunt book, gaunt pulls "the remainder of the Tanith 1st" off their homeworld. That was the remainder of their regiment. Later in the book he estimates that he has between 5-8 thousand troops. He doubles that when he adds the Vervunhive troops. When they are later reformed into the 81st 1st, they are finally at "full regiment" stength. Multiple battalions, tank units, artillery support, assault aircraft, and logistical support. About 20k men according to field reports in the book when it comes to "losses".

Again, this is entirely conjecture. A "regiment" could be 100k or 1k. GW has made it quite clear there is no real rules when it comes to definitions or facts. Terminators can both barely move due to their weight, and Back flip. Titans are impervious weapons of the machine god, And able to be "wounded" by a laspistol.

The only thing that we know about 40k, is there are zero rules, everything is made up, and none of it makes any sense.

That isn't quite true Fezz. When the Tanith 1st leave their burning homeworld they number around 3500. By the time of the Ghost's deployment to Monthax (the one with those Aeldari), they had reached 1500 and then the siege of Vervunhive depleted them even further. The Act of Consolidation allowed Vervunhivers to join the Ghosts and they reached a strength of around 2500. By the time they join with the Belladon and receive reinforcements from both Belladon and Verghast they sit at 19 regular companies and one unique company.
At no point did the Ghosts Regiment contain armour, aircraft, or artillery. They did have a fully staffed Medicae Corps with Dorden, Curth, Kolding, and various orderlies as well as a well-staffed Commissar pool with Gaunt, Hark, Ludd, Blenner and Fazikiel.

FezzikDaBullgryn wrote:

Again, this is entirely conjecture. A "regiment" could be 100k or 1k. GW has made it quite clear there is no real rules when it comes to definitions or facts. Terminators can both barely move due to their weight, and Back flip. Titans are impervious weapons of the machine god, And able to be "wounded" by a laspistol.

The only thing that we know about 40k, is there are zero rules, everything is made up, and none of it makes any sense.

Debatably all fiction is made up, its kinda the point; the best 40k work(sure there is the trashy stuff they use to market factions; such as a hormagaunt's claws beings uper hard and sharp and being able to slice through terminator armour, whilst terminator armour is all but indestructable) sticks to an agreed upon set of rules when it comes to how gak behaves and when something like a terminator copping a beam from a las pistol or a single round from an auto pistol and dying without *a satisfying reason* its pretty frickin jarring and its an example of piss poor writing.(admittedly doing something so exploitative of the physics of the world such as a space marine becoming a martyr by using jump packs to accelerate himself into the ground after reaching terminal velocity and impacting with an activated power fist to essentially release a similar amount of force to a hyrogen bomb would also be jarring, its not how the world is meant to work and the writer and reader have that unspoken contract)

. There is a pretty grass roots understanding that to kill a terminator you probably want some super energy weapon, or a battle tank's main gun.

My point is regardless of the numbers that are given, which are usually really really small and never scrape anywhere near some conflicts on our own world, are somehow meant to be vast and on an epic scale. A planetary scale.
What i put forwards is that instead of looking at unreliabley tiny numbers provided in the lore, we should be looking at context clues.
Such as a single regiment being considered sufficent to reinforce the PDF of a planet. If the planet is earth sized you'd need millions of troops to make a difference.

And you simpily cannot have the intended grandure and epicness of conflict by having a few thousand guys with a dozen tanks and a titan kicking it off on a planet the size of frickin Ireland.

My take on Regiments is that the Regiment number is actually the Battalion number. It seems to match the British Regiment system.

My own country, of NZ, as a commonwealth country also follows this system. But as a smaller colony (compared to India or Canada) we are under 1 regiment, the Royal NZ regiment. During WW2 this regiment fielded 3 divisions (maybe 2 its late).

Just like WW2 battalions they should be grouped in Brigades and Divisions as needed.

I think that we all agree GW numbers are way too low for major battles.

On Commissars 1 per regiment I see as default. With more attached as needed.

 OldMate wrote:
Behold the power and might of a typical cadian regiment. It's just scraping by at the bottom end of a battalion. Cadian regiments are apparently battalion strength.https://wh40k.lexicanum.com/wiki/Imperial_Guard_Regiment#/media/File%3ACadianRegimentsArt.jpg

These guys would definitely be turned into hamburgers by a company of space marines. Although the idea of them seizing or defending a planet bigger than a red dwarf planetoid is pretty laughable.

Those are not particularly typical regiments, despite Lexicanum's description, unless you are taking them as typical of understrength regiments that have likely suffered a lot of casualties. Three companies of three platoons each is near enough the minimum strength that could be considered a regiment, and it is very likely these regiments will be merged with other understrength regiments in the near future if they survive.

We know that Cadian infantry regiments are considerably larger at muster- the Cadian 114th mechanised under Colonel Stranski was ~4000 strong at the beginning of the Taros campaign, with ~12 mechanised infantry companies, 6 self-propelled artillery companies, 2 recon companies, and a headquarters company. It was apparently divided into 4 battalions on the FW TOE (they called them brigades, but this seems like an error in terminology). Likewise, 12 infantry companies of the Cafian 8th under Lord Castellan Creed constituted ~4000 troopers prior to the 13th Black Crusade, with this representing only half the tegiment- the other 4000 soldiers on other deployments.

Personally, I think context is important for understanding the image Lexicanum uses- most players now probably associate it with the 8th edition AM codex, but it first appeared in Apocalypse 1st edition as a supplement for 40k 4th edition. At the time, the current IG codex was the IG 3rd edition 2nd codex (usually known as 3.5), which featured a two page spread showing the 4000 soldiers in twelve companies of the Cadian 8th mentioned above (if you bother to count, it actually shows 24 companies, but I'm goimg off the published lore). In other words, GW at the time was well aware of what a full Cadian regiment looked like, but they chose to put the understrength one in the Apocalypse rulebook. I am fairly confident this is because the force depicted is actually of a size possible to field in a single Apocalypse battle and feasible to collect. In fact, I am fairly confident that the IG Youtuber Mordian Glory has a Guard force larger than that displayed. Plonking down 4000 troopers is a much less attainable goal to encourage players to collect.

The IG 3rd edition, 1st codex explicitly states that regiments are typically 3000-4000 strong. However, we also have multiple other explicit numbers over a fairly large range, such as the Valhallan 18th light infantry aving a founding strength of >120000, the Krieg 143rd siege regiment mustering at 200000, and the single largest I am aware of being the 50th Gudrun rifles with an initial strength of 750000 (upped from 500000). The numbers are variable between regiments, but we do have explicit numbers for many regiments.

My head cannon is either you have "regiments" with straight out 10-20 million soldiers. Of course this would mean that every regiment is some mix of infantry tanks, artillery and support. This would give a regiment somewhere near the frontage needed to hold a continent which would be vital in planetary warfare. It would also make sense as part of the planetary tithe. You are asking them to give up a considerable percentage of their prime working age manpower.

In ww2 there was about 70 million combatants, this is obviously including naval and airforce personnel.BUT the war was condensed to only a limited number of theatres. So the fighting strength of 3 "regiments" a pretty standard large war by 40k standards is in the same ball park as ww2 but before we figure in aerial assets and logistics and support; this puts us neatly into the epic scale of conflict they aspire to in 40k(and in many cases quite amusingly fail when numbers are comically small in what is meant to be a global war(i have a vivid imagination and can easily imagine tens or hundreds of thousands of troops strung out on a frontage of hundreds or thousands of kilometres, of tiny elements of armies clashing in squad level skirmishes along a thousand mile front because that is how thin they are forced to deploy). Or on the other hand that there is literally thousands of regiments in any conflict.

The issue with scaling guard up to deal with a planetary war is that Astates start to look really frickin irrelevant. Dispatched 100 space marines to reinforce a planet? In a war where there is 80 million troops per side? They had best be everywhere at once and individually have the striking power of an ICBM.

Hence why i put forwards the 'vastly unpopulated imperium' theory before. It is the inly way to make a space marine chapter strength deployment relevant in a global war(or a regiment having a single baneblade, its contending with dozens of enemy russes then, not tens of thousands of them); as 99% of depictions of them have space marines performing a shock role on the front lines. And it does not matter how good they are the disparity in firepower will quickly become apparent. And if the enemy hold the battlefield they cannot recover the geneseed.

Your headcanon for larger regiments is not consistent with established lore on the whole, although I am sure some regiments of that size exist.

However, the under-populated Imperium is largely true- the overall population is truly staggering, but looks to be highly concentrated on a small number of worlds. Pre-rift, only ~3% of Imperial worlds are hive worlds like Minea with its ~150 billion souls. Major forge worlds are probably similar in population but similarly rare. Civilised and other industrial worlds will have a population broadly comparable to modern Earth at an unknown frequency, and frontier, agri, mining, and death worlds all typically have low populations in the millions. Betalis III, for example, is a frontier mining world with a population of 130 million. This is a pretty low value in the scheme of things. Taros had a population of just 12 million prior to the Taros war.

Add to this that part of the setting is that the Imperium never has enough guardsmen to cover its needs- a good example is the Taros campaign, which received just ten regiments when the commanding officer thought they needed over twenty to prosecute the campaign successfully. The campaign failed. This is despite many Imperial worlds generating millions of troopers per annum to feed the meat grinder. The Imperium eats through bodies quickly.

I think the Imperium has the means to arm much larger numbers of troops, but not to deploy them and maintain discipline, which limits what it can do with its populations. For example, many Imperial citizens are oppressed underclasses force to toil in horrible conditions. They are frequently already rebellious and being beaten down by a class of enforcers. Arm too many at once as the world is just as liable to be lost through uprising as enemy action. Available transports to ship guard units around the Imperium, and escorts to protect them, are also a limiting factor.

As such, forces are frequently stretched thin and forced to operate on razor thin margins and make use of local resources to prevail. Often, an Imperial force will smash the main centres of resistance on a planet, and leave a single regiment to conduct planet-wide mop-up operations. This probably requires recruiting locals to form a new PDF, forming bases of operation, and consolidating from there. Such clean up can take decades or even generations.

Big worlds are explicitly noted as being beyond the means of most Imperial forces to recapture- when Krieg rebelled, for example, it was a prosperous and well fortified hive world. The Imperium basically took one look and said they'd deal with that later when enough force could be generated. It took 500 years and unleasing usually forbidden atomic weaponry for the single IG regiment on planet to retake the world.