I image this conflict going a lot like how it did for the US Marines during Vietnam, actually. It's going to be brutal. Though, thanks ranoncles, for the other engagements to have a look at.

I image this conflict going a lot like how it did for the US Marines during Vietnam, actually. It's going to be brutal.

Funny, I had the exact same thought.

And then tried to work from there.

Insurgencies and counter-insurgency operations are very sophisticated. The end goal is to control the country without challenge. Depending on the kind of game you are playing, you can safely ignore this but it should have some effect on the kind of missions you should plan.

In very general terms, the insurgents try to prevent the occupiers from controlling the country, i.e. raise taxes and have their administrative operations take root and govern the people. The counter-insurgency operations are generally aimed at ensuring the (local) government which is either a collaborative government or a parachuted government can perform the actions of a government; raise taxes, govern the people and provide basic security for those people that accept them as the government….The key is taxes (which require effective control…) If the occupier and or their puppet government can’t raise taxes to pay for their administration and military, the financial drain eventually becomes too much and their control collapses in the end as local administrators and troops go unpaid.

Following this, there are two kinds of insurgents. The first generally lives within the communities (cities, villages etc.) and who covertly commits acts of sabotage and murder (of enemy soldiers and collaborators) when they think they can get away with it. This is traditionally the farmer who kills a tax collector or straggling soldier with his axe and then hides the body. It is very difficult to identify such insurgents and thus occupying troops often resort to indiscriminate violence. Which often creates more insurgents….

The other kind is the organized band of insurgents. These bands generally live apart from the communities in difficult terrain (but rely upon sympathisers for food, new recruits etc.) where they can hide from the superior enemy forces and ambush their logistical tail or small isolated columns and raid supposedly safe communities where they kill local administrators and collaborators. These are often combatted by a combination of static garrisons and flying columns or concentric attacks by multiple columns to hem them into a killing zone. These insurgent bands rely on their knowledge of the terrain to escape enemy forces when they try to close in on their hideouts. The best way of tackling such bands are ‘similar bands’…either other locals (often from a racial minority) with the same knowledge of terrain or with special troops with much lighter equipment than the regular troops and which can thus manoeuvre the same way as the insurgents. For example, Napoleon organized French mountaineers into a special anti-partisan force who used their knowledge of mountaineering to chase the Spanish guerrillas while the Germans in WWII created special hunter teams of light infantry to take the fight to the partisans.

This is of course a very generic view but I hope it shows that insurgencies are very difficult to end without political compromise. A military solution requires a lot of troops (the often heard ‘boots on the ground' to provide both local garrisons to protect and control community centres and troops to chase the insurgents) and often takes years as insurgents are chased from hideout to hideout.

Okay, so translate that into M41 and aside Exterminatus, what are the options?

I mean, I could see some IG groups working with locals, but i have my doubts the ranking officers will give such an order.

Rather than go on at length about my theories - of which I have many - I'll just post some material from a previous Deathwatch campaign. I worked from the premise that the lists of forces present during the 3rd Armageddon War and 13th Black Crusade gave only representative samples, rather than being exhaustive TO&E lists. This document evolved over weeks of planning, to give something of what I felt was appropriate scale.

The Theron campaign was a small-to-medium counter-invasion of an Imperial world subjected to Tau dominion. The forces present during the campaign is as follows:

33rd Retaliation Group Imperial Navy (Detached Battlefleet Obscuras)

Commanding Officer: Admiral Wulfgang Richter Annerlitz-Verguβen

• Fist of Thracian (Mars-class Battlecruiser; Flagship)
  • 42nd Voidfighter Wing (Fury Interceptors; Flight Marshall Jonas Carranto)
  • 75th Void Bomber Wing (Starhawk Bombers; Wing Commander Thaddeus Orben)
  • 1380th Aeronautica Fighter Wing (Lightning Interceptors; Wing Commander Sebastin Kane)
  • 671st Aeronautica Bomber Wing (Marauder Bombers; Wing Commander Pieter Haran)
  • 1442nd Aeronautica Fighter Wing (Thunderbolt Fighters; Wing Commander Alain Choris)
• Count Szägen (Lunar-class Cruiser; Commodore Teodor Arill)
• Just Persecution (Dictator-class Cruiser; Captain Rafael Korrigan)
  • 88th Voidfighter Wing (Fury Interceptors; Wing Commander Abriel Huln)
  • 11th Void Bomber Wing (Starhawk Bombers; Flight Marshall Caspian Threnough
  • 2801st Aeronautica Fighter Wing (Lightning Interceptors; Wing Commander Matthias Kreel)
  • 635th Aeronautica Bomber Wing (Marauder Bombers; Wing Commander Solam Veddick)
  • 1645th Aeronautica Fighter Wing (Thunderbolt Fighters; Wing Commander Karl Astofen)
• Cypra Iustum (Tyrant-class Cruiser; Captain Xamuel Caidin)
• Indomitable (Gothic-class Cruiser; Captain Leander Cross)
• Solitary Defender (Dauntless-class Light Cruiser; Captain Lukas Frobischer)
• Forgotten Saint (Dauntless-class Light Cruiser; Captain Adrann Hess)
• Unknown Hero (Dauntless-class Light Cruiser; Captain Agaustin Raikk)
• Blade Squadron (Sword-class Frigates; Squadron CO Captain Augrym Theska)
• Lambent Squadron (Firestorm-class Frigates; Squadron CO Captain Deiran Vone)
• Serpent Squadron (Cobra-class Destroyers; Squadron CO Captain Halan Thennick)

442nd Army Group Imperial Guard (Subordinate to Greyhell Front Army Region, Canis Salient, Achilus Crusade)

Commanding Officer: Lord Commander Tomasz Heydrich

The 442nd Army Group consists of approximately 70 million Imperial Guardsmen, divided along traditional lines. Lord Commander Heydrich’s immediate subordinates are the nine Lord Generals, one commanding each Field Army. The Field Armies control all operations in one of the nine Administratum-denoted strategic regions of Theron.

Each Lord General is attended by six Generals, each commanding a single Corps, each of which in turn is comprised of six divisions, commanded by Lieutenant Generals and Major Generals, variously. Each Division consists of six Brigades, each commanded by a Brigadier General, and every Brigade contains six Regiments, each commanded by a Colonel.

In traditional Imperial Guard fashion, each Regiment is then comprised of several Companies (commanded by Majors or Captains), which each contain several Platoons, Squadrons, Batteries, etc. In total, there are 11,664 regiments present upon Theron.

First Army (Caedes Province – Central Command Garrison)

Commanding Officer: Lord General Surander Caelan (nominal; subordinate to Lord Commander Heydrich)

Second Army (Ebonspire Mountains Region)

Commanding Officer: Lord General Orzim Strauka

Third Army (Haruan Plains Region)

Commanding Officer: Field Marshall Baron Thuren Kristov Arun

Fourth Army (Paer Ceydon Province – Eastern Coastal & Wet Navy)

Commanding Officer: Lord General Alessaunder Menken-Varras

Fifth Army (Anas-Vyl Province)

Commanding Officer: Commander Abriel Thorne

Sixth Army (Stregani Province)

Commanding Officer: Lord General Vandar Serenno

Seventh Army (Thal Vegeer Province)

Commanding Officer: Lord General Edoard Baruhk

Eighth Army (Paer Rephel Province – Southern Coastal & Wet Navy)

Commanding Officer: Lord General Lorenzo Hamaskine

Ninth Army (Entir Forest Province)

Commanding Officer: Lord General Thaniel Komestoga

Departmento Munitorum Support Assets

• Support Brigade 3/981Δ, Ordinate-Majoris (Militant/Logistik) Enzer Nattic
• Commissariat detachment, Commissar-General Naxander Stromfels
• Divisio Tactica delegation, Primary Ordinate Ciro Durander
• Storm Trooper Regiment, 88th Battalion, Major Vos Korden
  • 68th Company, command Company
  • 298th Company, Captain Hiram Reschic
  • 111th Company, Captain Colen Hasz
  • 390th Company, Provost-Captain Silas Kevisch (on secondment to Commissar-General Stromfels as Military Police detachment)
  • Cross attached: Imperial Navy 1981st Transport

Task Force Broadsword (Adeptus Astartes)

Commanding Officer: Wolf Lord Haakon Greypelt, Space Wolves Chapter

Task Force Broadsword comprises the small Adeptus Astartes contingent present on Theron. Few in numbers, the Astartes presence has little theoretical authority with regards to the campaign itself, and operates autonomously from the 442nd Army Group, liaising with Lord Commander Heydrich and his General Staff as required but maintaining their own operations.

Task Force Broadsword is commanded by Wolf Lord Haakon Greypelt of the Space Wolves Chapter, whose Great Company comprises almost a third of the force. Haakon was given command by mutual agreement, due to having served the Imperium for over five hundred years and being the most senior Astartes present as a result. Second is the Justicars strike force, composed of the Chapter’s 4th Company plus support (Veteran, Armour and Scout elements), and commanded by Commander Alzir Toban. A small armoured vehicle contingent of Storm Wardens led by Brother-Sergeant Adan McCullough provides additional fire support to other Astartes operations.

Task Force Broadsword is due for reinforcement, as the Iron Knights 2nd Company in its entirety, aboard the Strike Cruiser Fist of Brycantia and commanded by Brother-Captain Hervald Strom (winner of the 812nd Feast of Blades), is en-route from the Maw. The Iron Knights are due to stop briefly at Strife to rendezvous with a Deathwatch Kill-Team also en-route to Theron.

Haakon Greypelt’s Great Company

Haakon Greypelt, Jarl of Dekk, has been on Theron since 5278817.M41, arriving alongside the Storm Wardens contingent. The 10th Great Company, under his command, have been fighting the Tau for six months, and have suffered some casualties in the process. The 10th consists of approximately 120 warriors, divided over fifteen packs – 4 Long Fangs packs, 4 Grey Hunter packs, 4 Blood Claw packs (one is Skyclaws, one is Swiftclaws), two Wolf Scout packs, and Haakon’s Wolf Guard, supported by Rhino and Razorback APCs, a trio of Predators, and the Wolf Guard Land Raider.

Greypelt is regarded as overall theatre commander for Adeptus Astartes forces on Theron.

Justicars 4th Company

[Details Incomplete]

Storm Wardens Armoured Assault Group

The Storm Wardens Armoured Assault Group, codenamed “Thunderhead”, is a small group intended to operate in support of other Imperial forces as a fast mobile reserve. It consists of a collection of Astartes drawn from the 2nd Company and Armoury of the Storm Wardens Chapter, under the command of Brother-Sergeant Adan McCullough. The force consists of the 3rd Tactical Squad, transported by the Razorbacks Sword of Sacris and Persecutor, supported by the Tech-Marines Eymon Gethryn and Artur Orm, along with the Predators Remorseless and Stormbringer (Annihilator and Destructor, respectively) and the Land Raider Thunder's Call. These are borne to battle by the Thunderhawk Transporters Chariot, Storm’s Herald and Tempestus.

Iron Knights 2nd Company Strike Force

Commanded by Hervald Strom, current reigning champion of the Feast of Blades, the 2nd Company of the Iron Knights Chapter are the newest additions to the Astartes Task Force on Theron, due to arrive on 5776817.M41 with the support of Deathwatch Kill-Team Talon. Their Strike Cruiser, the Fist of Brycantia will remain in-system to provide support to Imperial Navy planetary assault, commanded by Shipmaster Leos Vogt.

The Iron Knights are a Codex Chapter, and consequently the 2nd Company falls within the normal structures of an Astartes Battle Company, as follows:

• Brother-Captain Hervald Strom, commanding officer
  • Command Section consisting of Veteran Brother Dietrich, Brother-Apothecary Stenn, Brother-Sergeant Koren, Brother-Champion Recht and Revered Brother (Banner Bearer) Sieger.
• Brother-Chaplain Tyro Kurgen
• Brother-Epistolary Meron Thane
• Honoured Brother Valoy, Dreadnought
• Honoured Brother Demetrius, Ironclad Dreadnought
• 6 Tactical Squads, 2 Assault Squads, 2 Devastator Squads
• 10 Rhinos, 1 Razorback
• Armoury Detachment: 6 Predators Destructor, 4 Predators Annihilator, 3 Vindicators
• Fleet Detachment: 12 Thunderhawk Gunships, 12 Thunderhawk Transporters
• First Company Detachment: Squad Nihilus (Sternguard), in Tactical Dreadnought Armour, led by Brother-Sergeant Hano Nihilus.

Adeptus Titanicus Quatro-Legio - Legio Fulminare

Commanding Officer: Legate-Princeps Hadrazael Kaan (represented by his Equerry, Moderatus-Primus Athric Quos)

12 Engines (under strength):

• Contemno Aeturnum (Warlord-class Battle Titan)
• Deus Vocis (Warlord-class Battle Titan)
• Fiat Ignis (Warlord-class Battle Titan)
• Excoriare (Reaver-class Battle Titan)
• Vereor Apparatus (Reaver-class Battle Titan)
• Dies Bellum (Reaver-class Battle Titan)
• Barbarus and Ferus (Warhound-class Scout Titans)
• Contemno and Abominor (Warhound-class Scout Titans)
• Lupus and Vulpes (Warhound-class Scout Titans)

So, in summary... a lot of military assets. And this isn't complete - there's still the Adeptus Mechanicus contingent (and their accompanying Skitarii phalanx) undetailed. Tens of millions of warriors, fighting a protracted planetary war.

The Astartes are there as a point of comparison. Nobody does concentration of force like the Astartes, and it's a truism of Imperial warfare that a squad of Space Marines is far greater than the sum of its parts. If each Space Marine is worth ten guardsmen, and each squad of ten Astartes is worth more than the individual might of the warriors that comprises it, then a single tactical squad could easily be argued to have tactical and strategic might comparable to three full platoons of Guardsmen. Potent, yet compact - considerable force contained within a far smaller number of warriors and thus able to hit a target with greater coordination and precision than a comparably-strong force of Guardsmen. No better force exists for line-breaking, surgical strikes and similarly swift, crippling actions, and the dread they engender because of their inhuman efficacy only makes them more effective in that role.

The Imperial Guard break and gouge and blast their foes apart on a large scale. The Astartes deal catastrophic blows to strategic weak spots. Both are needed to truly and utterly subjugate a world, but to merely claim one can be achieved by a force of Astartes in a startlingly short space of time, crippling a foe's ability to effectively retaliate and compelling surrender through abject terror of the Emperor's Angels of Death. It is why the Astartes have been at the forefront of the most brutal wars for more than hundred centuries - they can achieve quickly what would be difficult for mortal forces, and attempt what would otherwise be impossible.

_{That's quite the order of battle you got there. The engagement i'm talking about is actually much less serious business. Though if i had all of that to deal with the problem i outlined, BWAHAHAHA.}

The Theron campaign was a small-to-medium counter-invasion of an Imperial world subjected to Tau dominion. The forces present during the campaign is as follows:

Small-to-medium counter-invasion for an imperial World?

More likely an entire crusade... or several.

I worked from the premise that the lists of forces present during the 3rd Armageddon War and 13th Black Crusade gave only representative samples, rather than being exhaustive TO&E lists.

The 13th Black Crusade one, yes. The Armageddon 3 list, no.

But since artistic licence allows all of us to change such details on a whim, there is always the option of simply replacing those lists with one's own interpretation of warfare in the 41st millennium. The Forge World studio seems to prefer vastly bigger army groups than GW's core team, too, I think.

Rather than go on at length about my theories - of which I have many - I'll just post some material from a previous Deathwatch campaign. I worked from the premise that the lists of forces present during the 3rd Armageddon War and 13th Black Crusade gave only representative samples, rather than being exhaustive TO&E lists. This document evolved over weeks of planning, to give something of what I felt was appropriate scale.

The Theron campaign was a small-to-medium counter-invasion of an Imperial world subjected to Tau dominion. The forces present during the campaign is as follows:

33rd Retaliation Group Imperial Navy (Detached Battlefleet Obscuras)

Commanding Officer: Admiral Wulfgang Richter Annerlitz-Verguβen

• Fist of Thracian (Mars-class Battlecruiser; Flagship)
  • 42nd Voidfighter Wing (Fury Interceptors; Flight Marshall Jonas Carranto)
  • 75th Void Bomber Wing (Starhawk Bombers; Wing Commander Thaddeus Orben)
  • 1380th Aeronautica Fighter Wing (Lightning Interceptors; Wing Commander Sebastin Kane)
  • 671st Aeronautica Bomber Wing (Marauder Bombers; Wing Commander Pieter Haran)
  • 1442nd Aeronautica Fighter Wing (Thunderbolt Fighters; Wing Commander Alain Choris)
• Count Szägen (Lunar-class Cruiser; Commodore Teodor Arill)
• Just Persecution (Dictator-class Cruiser; Captain Rafael Korrigan)
  • 88th Voidfighter Wing (Fury Interceptors; Wing Commander Abriel Huln)
  • 11th Void Bomber Wing (Starhawk Bombers; Flight Marshall Caspian Threnough
  • 2801st Aeronautica Fighter Wing (Lightning Interceptors; Wing Commander Matthias Kreel)
  • 635th Aeronautica Bomber Wing (Marauder Bombers; Wing Commander Solam Veddick)
  • 1645th Aeronautica Fighter Wing (Thunderbolt Fighters; Wing Commander Karl Astofen)
• Cypra Iustum (Tyrant-class Cruiser; Captain Xamuel Caidin)
• Indomitable (Gothic-class Cruiser; Captain Leander Cross)
• Solitary Defender (Dauntless-class Light Cruiser; Captain Lukas Frobischer)
• Forgotten Saint (Dauntless-class Light Cruiser; Captain Adrann Hess)
• Unknown Hero (Dauntless-class Light Cruiser; Captain Agaustin Raikk)
• Blade Squadron (Sword-class Frigates; Squadron CO Captain Augrym Theska)
• Lambent Squadron (Firestorm-class Frigates; Squadron CO Captain Deiran Vone)
• Serpent Squadron (Cobra-class Destroyers; Squadron CO Captain Halan Thennick)

442nd Army Group Imperial Guard (Subordinate to Greyhell Front Army Region, Canis Salient, Achilus Crusade)

Commanding Officer: Lord Commander Tomasz Heydrich

The 442nd Army Group consists of approximately 70 million Imperial Guardsmen, divided along traditional lines. Lord Commander Heydrich’s immediate subordinates are the nine Lord Generals, one commanding each Field Army. The Field Armies control all operations in one of the nine Administratum-denoted strategic regions of Theron.

Each Lord General is attended by six Generals, each commanding a single Corps, each of which in turn is comprised of six divisions, commanded by Lieutenant Generals and Major Generals, variously. Each Division consists of six Brigades, each commanded by a Brigadier General, and every Brigade contains six Regiments, each commanded by a Colonel.

In traditional Imperial Guard fashion, each Regiment is then comprised of several Companies (commanded by Majors or Captains), which each contain several Platoons, Squadrons, Batteries, etc. In total, there are 11,664 regiments present upon Theron.

First Army (Caedes Province – Central Command Garrison)

Commanding Officer: Lord General Surander Caelan (nominal; subordinate to Lord Commander Heydrich)

Second Army (Ebonspire Mountains Region)

Commanding Officer: Lord General Orzim Strauka

Third Army (Haruan Plains Region)

Commanding Officer: Field Marshall Baron Thuren Kristov Arun

Fourth Army (Paer Ceydon Province – Eastern Coastal & Wet Navy)

Commanding Officer: Lord General Alessaunder Menken-Varras

Fifth Army (Anas-Vyl Province)

Commanding Officer: Commander Abriel Thorne

Sixth Army (Stregani Province)

Commanding Officer: Lord General Vandar Serenno

Seventh Army (Thal Vegeer Province)

Commanding Officer: Lord General Edoard Baruhk

Eighth Army (Paer Rephel Province – Southern Coastal & Wet Navy)

Commanding Officer: Lord General Lorenzo Hamaskine

Ninth Army (Entir Forest Province)

Commanding Officer: Lord General Thaniel Komestoga

Departmento Munitorum Support Assets

• Support Brigade 3/981Δ, Ordinate-Majoris (Militant/Logistik) Enzer Nattic
• Commissariat detachment, Commissar-General Naxander Stromfels
• Divisio Tactica delegation, Primary Ordinate Ciro Durander
• Storm Trooper Regiment, 88th Battalion, Major Vos Korden

• 68th Company, command Company
• 298th Company, Captain Hiram Reschic
• 111th Company, Captain Colen Hasz
• 390th Company, Provost-Captain Silas Kevisch (on secondment to Commissar-General Stromfels as Military Police detachment)
• Cross attached: Imperial Navy 1981st Transport

Task Force Broadsword (Adeptus Astartes)

Commanding Officer: Wolf Lord Haakon Greypelt, Space Wolves Chapter

Task Force Broadsword comprises the small Adeptus Astartes contingent present on Theron. Few in numbers, the Astartes presence has little theoretical authority with regards to the campaign itself, and operates autonomously from the 442nd Army Group, liaising with Lord Commander Heydrich and his General Staff as required but maintaining their own operations.

Task Force Broadsword is commanded by Wolf Lord Haakon Greypelt of the Space Wolves Chapter, whose Great Company comprises almost a third of the force. Haakon was given command by mutual agreement, due to having served the Imperium for over five hundred years and being the most senior Astartes present as a result. Second is the Justicars strike force, composed of the Chapter’s 4th Company plus support (Veteran, Armour and Scout elements), and commanded by Commander Alzir Toban. A small armoured vehicle contingent of Storm Wardens led by Brother-Sergeant Adan McCullough provides additional fire support to other Astartes operations.

Task Force Broadsword is due for reinforcement, as the Iron Knights 2nd Company in its entirety, aboard the Strike Cruiser Fist of Brycantia and commanded by Brother-Captain Hervald Strom (winner of the 812nd Feast of Blades), is en-route from the Maw. The Iron Knights are due to stop briefly at Strife to rendezvous with a Deathwatch Kill-Team also en-route to Theron.

Haakon Greypelt’s Great Company

Haakon Greypelt, Jarl of Dekk, has been on Theron since 5278817.M41, arriving alongside the Storm Wardens contingent. The 10th Great Company, under his command, have been fighting the Tau for six months, and have suffered some casualties in the process. The 10th consists of approximately 120 warriors, divided over fifteen packs – 4 Long Fangs packs, 4 Grey Hunter packs, 4 Blood Claw packs (one is Skyclaws, one is Swiftclaws), two Wolf Scout packs, and Haakon’s Wolf Guard, supported by Rhino and Razorback APCs, a trio of Predators, and the Wolf Guard Land Raider.

Greypelt is regarded as overall theatre commander for Adeptus Astartes forces on Theron.

Justicars 4th Company

[Details Incomplete]

Storm Wardens Armoured Assault Group

The Storm Wardens Armoured Assault Group, codenamed “Thunderhead”, is a small group intended to operate in support of other Imperial forces as a fast mobile reserve. It consists of a collection of Astartes drawn from the 2nd Company and Armoury of the Storm Wardens Chapter, under the command of Brother-Sergeant Adan McCullough. The force consists of the 3rd Tactical Squad, transported by the Razorbacks Sword of Sacris and Persecutor, supported by the Tech-Marines Eymon Gethryn and Artur Orm, along with the Predators Remorseless and Stormbringer (Annihilator and Destructor, respectively) and the Land Raider Thunder's Call. These are borne to battle by the Thunderhawk Transporters Chariot, Storm’s Herald and Tempestus.

Iron Knights 2nd Company Strike Force

Commanded by Hervald Strom, current reigning champion of the Feast of Blades, the 2nd Company of the Iron Knights Chapter are the newest additions to the Astartes Task Force on Theron, due to arrive on 5776817.M41 with the support of Deathwatch Kill-Team Talon. Their Strike Cruiser, the Fist of Brycantia will remain in-system to provide support to Imperial Navy planetary assault, commanded by Shipmaster Leos Vogt.

The Iron Knights are a Codex Chapter, and consequently the 2nd Company falls within the normal structures of an Astartes Battle Company, as follows:

• Brother-Captain Hervald Strom, commanding officer
  • Command Section consisting of Veteran Brother Dietrich, Brother-Apothecary Stenn, Brother-Sergeant Koren, Brother-Champion Recht and Revered Brother (Banner Bearer) Sieger.
• Brother-Chaplain Tyro Kurgen
• Brother-Epistolary Meron Thane
• Honoured Brother Valoy, Dreadnought
• Honoured Brother Demetrius, Ironclad Dreadnought
• 6 Tactical Squads, 2 Assault Squads, 2 Devastator Squads
• 10 Rhinos, 1 Razorback
• Armoury Detachment: 6 Predators Destructor, 4 Predators Annihilator, 3 Vindicators
• Fleet Detachment: 12 Thunderhawk Gunships, 12 Thunderhawk Transporters
• First Company Detachment: Squad Nihilus (Sternguard), in Tactical Dreadnought Armour, led by Brother-Sergeant Hano Nihilus.

Adeptus Titanicus Quatro-Legio - Legio Fulminare

Commanding Officer: Legate-Princeps Hadrazael Kaan (represented by his Equerry, Moderatus-Primus Athric Quos)

12 Engines (under strength):

• Contemno Aeturnum (Warlord-class Battle Titan)
• Deus Vocis (Warlord-class Battle Titan)
• Fiat Ignis (Warlord-class Battle Titan)
• Excoriare (Reaver-class Battle Titan)
• Vereor Apparatus (Reaver-class Battle Titan)
• Dies Bellum (Reaver-class Battle Titan)
• Barbarus and Ferus (Warhound-class Scout Titans)
• Contemno and Abominor (Warhound-class Scout Titans)
• Lupus and Vulpes (Warhound-class Scout Titans)

So, in summary... a lot of military assets. And this isn't complete - there's still the Adeptus Mechanicus contingent (and their accompanying Skitarii phalanx) undetailed. Tens of millions of warriors, fighting a protracted planetary war.

The Astartes are there as a point of comparison. Nobody does concentration of force like the Astartes, and it's a truism of Imperial warfare that a squad of Space Marines is far greater than the sum of its parts. If each Space Marine is worth ten guardsmen, and each squad of ten Astartes is worth more than the individual might of the warriors that comprises it, then a single tactical squad could easily be argued to have tactical and strategic might comparable to three full platoons of Guardsmen. Potent, yet compact - considerable force contained within a far smaller number of warriors and thus able to hit a target with greater coordination and precision than a comparably-strong force of Guardsmen. No better force exists for line-breaking, surgical strikes and similarly swift, crippling actions, and the dread they engender because of their inhuman efficacy only makes them more effective in that role.

The Imperial Guard break and gouge and blast their foes apart on a large scale. The Astartes deal catastrophic blows to strategic weak spots. Both are needed to truly and utterly subjugate a world, but to merely claim one can be achieved by a force of Astartes in a startlingly short space of time, crippling a foe's ability to effectively retaliate and compelling surrender through abject terror of the Emperor's Angels of Death. It is why the Astartes have been at the forefront of the most brutal wars for more than hundred centuries - they can achieve quickly what would be difficult for mortal forces, and attempt what would otherwise be impossible.

The Theron campaign was a small-to-medium counter-invasion of an Imperial world subjected to Tau dominion. The forces present during the campaign is as follows:

Small-to-medium counter-invasion for an imperial World?

More likely an entire crusade... or several.

Nope, N0-1_H3r3's numbers seem about right to me (though the number of Astartes and Titans points to a very well-connected commander). Consider that we on today's Earth have several tens of millions of soldiers if you count the reserves which would be mobilized against planetary invasion - and the worlds of WH40K often don't stop at a mere 7 billion people. If you want a force that can actually conquer a planet without massively relying on local sympathies, you need roughly equivalent numbers at least.

That warmaster from the first page with his half million appears rather ridiculous when you consider that World War II saw over a hundred million soldiers fighting.

That warmaster from the first page with his half million appears rather ridiculous when you consider that World War II saw over a hundred million soldiers fighting.

Only if we completely dismiss the weapons of mass destruction fielded in M41, from Vortex missiles to planetary bombardment. WW2 would have been over in a week if either side had a battleship in orbit.

In fact, Japan's surrender after two nukes probably is testament to this.

[edit] I think there's two types of interpretations put forth by the people in this thread:

The "low numbers school" that looks at the limitations of intersteller transportation and the options presented by the military hardware within the setting,

and the "high numbers school" that compares the conflicts in Wh40k to Earth's own history, basically scaling up the numbers of historical battles as wars in 40k involve entire planets or even star systems.

As with almost all background in this franchise, both approaches are valid - they simply depend on individual perspective, and (or so I think) what sort of books we've read on the setting itself. Depending on the exact origin, official sources including licensed material have referenced and/or supported both schools of thought in the past.

The Theron campaign was a small-to-medium counter-invasion of an Imperial world subjected to Tau dominion. The forces present during the campaign is as follows:

Small-to-medium counter-invasion for an imperial World?

More likely an entire crusade... or several.

Perhaps. But I've long worked with the (entirely unofficial) notion that the total population of the Imperium is somewhere in the region of 3.3E+17 (derived from figures in the 3rd edition Warhammer 40,000 rulebook), and that planetary population figures in the RPGs tend to be orders of magnitude too low.

The force I listed - just over eleven and a half thousand regiments, some thirty-five million men - covers a single front within a single Salient of the Achilus Crusade. The Salient itself would be 10-20 times as large - somewhere between a 150,000 and 200,000 regiments - and each of the Salients is only about a third of the whole Crusade. Rough estimate, assuming a mean of 10 companies (300 men per company, per Infantry standard) per regiment, we're talking about the Crusade's ground forces alone consisting of well over one and a half billion men (short billion) spread across around half a million regiments. The numbers I work with, that's still a tiny fraction of the forces available to the Imperium of Man, scattered across innumerable warzones.

And that's without considering the naval forces involved. The fleet I listed is perhaps larger than is typical for the force it accompanies, but it's commensurate to the known Kor'vattra (Tau fleet) forces known to be operating in and around Theron (It's basically a 2000 point BFG fleet). The fleet's combined crew probably numbers around seven hundred thousand souls, meaning that there are fifty men on the ground for every one aboard ship, not including the troop transports (of which there would have been many). And, all that aside, when you've got tens of thousands of men in every starship, having ground forces that pale in comparison to the number of ratings in the fleet that carried them seems improper.

The thing to remember is that military force concentrates in places where it's necessary to have military force. Some sectors may have only the tiniest numbers of troops and ships present. Active warzones and threatened regions will have forces large enough to populate whole cities, even whole planets, operating within them.

That warmaster from the first page with his half million appears rather ridiculous when you consider that World War II saw over a hundred million soldiers fighting.

Only if we completely dismiss the weapons of mass destruction fielded in M41, from Vortex missiles to planetary bombardment. WW2 would have been over in a week if either side had a battleship in orbit.

In fact, Japan's surrender after two nukes probably is testament to this.

[edit] I think there's two types of interpretations put forth by the people in this thread:

The "low numbers school" that looks at the limitations of intersteller transportation and the options presented by the military hardware within the setting,

and the "high numbers school" that compares the conflicts in Wh40k to Earth's own history, basically scaling up the numbers of historical battles as wars in 40k involve entire planets or even star systems.

As with almost all background in this franchise, both approaches are valid - they simply depend on individual perspective, and (or so I think) what sort of books we've read on the setting itself. Depending on the exact origin, official sources including licensed material have referenced and/or supported both schools of thought in the past.

Thing is, men are expendable. Planets are not. Weapons of mass destruction deal more damage to planets than is desirable, so they are used sparingly. Vast quantities of soldiers can be sent into a conflict zone and act more thoroughly and with less irrevocable desolation than blind saturation bombardment from orbit. Weapons of mass destruction have its place... but a lot of the time, you need boots on the ground to secure the planet.

Further, the forces arrayed against the Imperium are much less likely to capitulate after a couple of small nukes. They often have much less willingness to relent than human forces throughout history, and the kinds of forces who are likely to withdraw are the kinds of forces who don't regard the holding of territory in the same way or who have completely different objectives. Just as importantly, everyone has those kinds of weapons - and they all have reasons not to rely heavily upon them.

Thing is, men are expendable. Planets are not. Weapons of mass destruction deal more damage to planets than is desirable, so they are used sparingly. Vast quantities of soldiers can be sent into a conflict zone and act more thoroughly and with less irrevocable desolation than blind saturation bombardment from orbit. Weapons of mass destruction have its place... but a lot of the time, you need boots on the ground to secure the planet.

Further, the forces arrayed against the Imperium are much less likely to capitulate after a couple of small nukes. They often have much less willingness to relent than human forces throughout history, and the kinds of forces who are likely to withdraw are the kinds of forces who don't regard the holding of territory in the same way or who have completely different objectives. Just as importantly, everyone has those kinds of weapons - and they all have reasons not to rely heavily upon them.

Arguably, all of this is a matter of interpretation, too - I guess we just happen to follow different ones. In terms of collateral damage, for example, I keep in mind that the majority of worlds in 40k may not look like contemporary Earth. Many of the planets may fall into the feral/feudal, agri, or hive world category, and collateral damage within such environments either doesn't concern the higher-ups, or it is unlikely.

Take Armageddon, for example, where almost all of its population and industry are huddled together in a few huge hives. Anything outside these giant cities, from the oceans to the jungles to the deserts, is a no-holds-barred zone where entire square kilometers of ground (and the forces on top) may get obliterated without anyone raising an eyebrow. Excepting a few sorties and clashes outside the walls, this effectively forces the defenders into the cities, which (a) may not be able to support them all, and (b) forces the attackers to start a siege, anyways.

For this reason, and because it fits to the studio fluff I've read so far, I think that the Imperium is much less concerned about environmental damage and may, in fact, simply prefer to "reduce and rebuild", as venkelos put it on the previous page. It is the grimdark™ pragmatic realisation that, with the kind of enemies the IoM is facing, and the kind of environment the IoM is fighting for/on, collateral damage is unavoidable, so they may just as well go "all in" right from the beginning. If there's something truly irreplaceable, I'm sure it would be considered important enough to send the Space Marines, who are experts at quickly securing strategically important areas long enough for reinforcements to arrive.

A questionable assessment? Perhaps. But I find this easier to believe than multiple millions of troops being transported across the Immaterium even for minor battles if space travel is supposed to be a rare and special thing in this setting.

But, I'm also operating on the crew sizes provided by Andy Chambers rather than what's provided in the Rogue Trader RPG books (sidenote: that short story he mentions was eventually published in the "Dark Imperium" anthology).

Further, the forces arrayed against the Imperium are much less likely to capitulate after a couple of small nukes. They often have much less willingness to relent than human forces throughout history, and the kinds of forces who are likely to withdraw are the kinds of forces who don't regard the holding of territory in the same way or who have completely different objectives. Just as importantly, everyone has those kinds of weapons - and they all have reasons not to rely heavily upon them.

It's not about capitulation - or not entirely, at least - but simply the ability to reduce an enemy's forces and fortifications to ashes without them being able to prevent it.

The Imperium not relying on massive orbital bombardment to support its invasions would quite simply contradict the original studio material, so this bit is a matter of "let's agree to disagree".

Though, of course, a case could be made for the medium ground between the "boots on the ground" and all-out nuking everything as well. The Imperium does have bomber formations, after all, and orbital strikes may not always refer to all-out destruction, but at least in GW's material may very well mean pinpoint damage limited to a specific location or enemy unit. At the end of the day, the important thing to remember - and the difference to WW2 - is that in a planetary invasion, no-one is safe anywhere, regardless of which side of the planet they're on or what sort of building they hide in. They'll either get obliterated or besieged, depending on how hard they are to crack.

The "low numbers school" that looks at the limitations of intersteller transportation and the options presented by the military hardware within the setting,

I'll grant you the military hardware (when it's used), but if you're not capable of ferrying a few million men and women across the void, you have no business feeding the billions of a hive world either. Additionally, quite a bit of setting material has presented the guard's wars as very much like those of today (and yesterday... and several centuries ago...), except for the fact that they're fought with extremely low manpower. Trench warfare isn't something that you engage in when the enemy is already on the run...

I think it is a mathematical fallacy to assume that if world X has y number of inhabitants, you'd need approximately y number of troops. The Soviet Union, when faced with a genocidal war in WWII, conscripted roughly 35 million troops during the entire war (thus there never were 35 million troops under arms at any time) out of a total population of roughly 200 million. And that was considered an extreme effort. The Germans and their allies usually had between 2 and 4 million troops on the Eastern front during the war.

So simply looking at numbers is not the way to go.

The Achilus crusade has 30 billion troops after considerable reinforcement and that is a full fledged attempt to reconquer a sector (about 200 inhabited planets?) so N0-1_H3r3's numbers of 70 million troops for a small-to-medium invasion of a single world sounds quite reasonable. With the caveat that less than 30% of those 70 million would be actual combat troops. The vast majority would be myriad support forces which I don't see in his order of battle. I know its not sexy but logistics, engineering, medical etc. take up much more manpower than combat. Tooth to tail is major factor and is hardly ever addressed.

@ranoncles

While I agree that one can't provide an exact formula for planetary invasions, it's certainly possible to eyeball forces as several orders of magnitude too small by looking at the conflicts of our world.

I'd say that depends on your capabilities to positioning what forces you have available, and your options on reducing the enemy number or force them to move to a specific location. If we are still comparing 40k to our real Earth (which I consider a dangerous approach, due to technological and methodical differences), then we also need to look at how various large realms were threatened by much smaller outside forces. In short: it doesn't matter if you have a hundred times the number of troops as your enemy, as long as they are scattered throughout the planet and it is the enemy who chooses the battle site.

Regarding support elements such as logistics, medical and engineering, I'm seeing IG regiments far closer to the armies of the Napoleonic Age than the "bloated" units of contemporary modern military forces, but this is just extrapolation from Codex fluff regarding the tithing and training/equipping of new IG regiments, and the lack of any support elements in GW's regimental organisation charts.

As for hive worlds, I don't actually think that they rely on outside supplies entirely - large parts of the population, especially the underhive section, may be limited to locally grown fungi or recycled organic material rather than having access to offworld products, which I'd consider more for the middle and higher classes rather than the rabble - though there could be some "trickle down economics" involved.

Also, I'd say hive worlds are actually the minority of planets in the Imperium (at least going by the BFG random sector generator), hence the mercantile fleets required to support them may still be small if you consider the entirety of the Imperium.

Of course, at the end of the day it's also important to consider what the Imperium's objective would actually be. If a hive world has been taken over by a traitorous government, it may be more prudent to focus on decapitating the leadership and try to win back the world with a minimum of collateral damage - compared to, say, the reaction to an outbreak of cult activity and warp phenomena. Case in point, as another example from the old Armageddon 3 background: the obliteration of the planet Khattar via orbital bombardment by Inquisitorial mandate, even after the corrupted priesthood that turned the ruling castes to the worship of Slaanesh had already been killed by the Celestian Lions.

... actually, that makes me wonder how many people on a hive would even notice a war going on if they're dwelling a kilometer below ground, only busying themselves with the constant gang troubles and how to survive until the next day.

"Say, who's our governor right now?"

I thought Navy, Mechanicus and Munitorum all supported the IG. The guard have bandaids and a few mechs, as well as comm techs, but for the most part, the Navy ferries them about and provides air support, the Mechanicus fixes/maintains their war machines and the Munitorum supplies them with the gear they get (note i didn't say need).

If that's how things actually work (and not just my own personal deduction) then it seems normal for the battle roster to just list a bunch of regiments, because the other groups aren't part of the Guard.

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.

Thing is, many millions or billions of people being moved around is rare Warp Travel - the population of the Imperium is far, far larger than mere billions. As I've said, I've been working from an approximate population of the Imperium as about a third of a quintillion (3.3E+17, or 330,000,000,000,000,000 - an assumption derived from a studio source, that I've worked with for over a decade), and only about 0.1% of the population is part of the Imperial Guard (seems like a reasonable, if low, value given the militarised nature of the Imperium - about a third the proportionate size of the US Army, and a similar proportion of civilian-to-soldier as the People's Republic of China), then you'd have a total number of Guardsmen of about three hundred and thirty trillion - you'd have a thousand souls for every soldier.

Moving half a million men to a warzone... that's an insignificant movement of men to an Imperium of the scale I've mentioned. It's about 0.15% of the total fighting strength of the organisation, notionally equivalent to the United States Army moving about 1,700 men (a couple of Battalions).

Now, obviously, 0.1% of the population in the Imperial Guard doesn't assume an even spread across the galaxy. Some worlds militarise 90%+ of their populations (Cadia is the iconic example, but far from the only one), others only muster troops as necessity requires. It's also an inconsistent value - the natural cycle of casualties and recruitment means that the actual proportion will grow and shrink frequently.

On the subject of collateral damage... no, there aren't many worlds like Earth. But that actually makes them more valuable. And the ones that aren't like Earth are valuable for other reasons. Every world is a resource that cannot be easily replaced. If you're warring across an Agri-world, then the conflict itself is deleterious to local infrastructure - it can't effectively produce food for nearby worlds while currently a warzone, and a war that cripple's that world's ability to sustain future macro-scale agriculture is a far greater loss than the lives of hundreds of thousands, even millions of men. Hive worlds aren't the only planets dependent on off-world resources, afterall, and off-world resources covers far more than just food. Raw materials for manufacture, and the products of that manufacture must be in perpetual motion around the Imperium - metal ores and unrefined promethium and valuable chemicals sent to industrialised, forge and hive worlds to be turned by colossal manufactories into the machinery (including, but not limited to, weapons and armour) needed to keep the Imperium going for another generation. The inconsistent spread and relative scarcity of technical knowledge means that conflicts on industrialised worlds can be as harmful as those on worlds producing food or raw materials - what happens if your industrial capabilities are virtually irreplaceable?

Now, the Imperium will at times consider the destruction of the world (whether in absolute terms, or in terms of its utility) to be the better option - certain enemies can't be eradicated without extreme measures, and the infrastructure of the Imperium couldn't function without a degree of redundancy in its component planets (infrastructure is typically built on a local - sector or subsector - level to minimise wide-scale disruption caused by conflict or disaster, and to ensure that most warp travel is over relatively short, relatively safe distances), meaning that few worlds are utterly irreplaceable. Still, I don't regard the utilisation of weapons of mass destruction to be mutually exclusive to massed ground forces - some of the most destructive weapons require terrestrial deployment (Titans being the best example), but I don't regard "take off and nuke them from orbit" to be the first choice of any commander, but rather a single tool in the toolbox.

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.

The "low numbers school" that looks at the limitations of intersteller transportation and the options presented by the military hardware within the setting,

I'll grant you the military hardware (when it's used), but if you're not capable of ferrying a few million men and women across the void, you have no business feeding the billions of a hive world either.

Exactly; when you have worlds that can't sustain themselves in isolation, that are home to hundreds of billions, even trillions of people, you need to be able to move quantities of food and raw materials that defy comprehension on a regular basis.

Further, as much as space travel may be defined as a rarity, it's also an utter necessity - the Imperium is built with the concept of relatively stable, routine logistical space travel (that is, space travel to maintain the gross structure of civilisation) in mind. It's why Navigators exist, why there are stable charted routes through each sector, and why Hive Worlds can even exist in the first place. 99% of people may never leave their homeworlds (though, again, this is not an even spread - the proportion will vary massively from world to world). The ones who do will likely spend a lot of time in space throughout their lives. For those born on spacecraft, interstellar travel is likely to be fairly commonplace.

And that's before you consider that interstellar travel in the Imperium still allows for interplanetary pilgrimages to shrine worlds and other sacred locations (as shown in many sources, not least of which the original Codex Sisters of Battle). Such pilgrims will probably never return home, likely living and dying as they voyage across the galaxy or at their destination (such was the idea I used to define the Maccabean Janissaries in the Only War rulebook).

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.

Ah, now it is getting easier for me to understand you. Though you have to admit that this "flawed approach" is a key-element of the WH40k lore. On one hand we have the Judge Dredd Inspired Mega Cities that even culminate into Hives, on the other hand we have the WH40k "grimdarkness" that tries to create a feeling of humanities struggle to survive. Mankind seeks populations centers for the protection they offer. The theme is around "bastions" or "forts" that offer some kind of protection, a thematic you get in most fiction that is about constant conflict etc.

I agree that this approach is flawed in most sci-fi scenarios where people arrive on new worlds that only seem to have one town but in WH40k it is understandable to some degree. If you think about it most battles in the lore, not the TT, are about sieges. And in most of this battles the defenders, in this case the imperials, would have lost if they had not concentrated their forces around several, defendable strongholds and waited for reinforcements. This tries to catch the atmosphere of the siege of a medieval castle (the entire "gothic" aesthetic aims at that) and this you cant compare to WW2 scenarios.

WH40k has its absurdities but does explain them to a degree. Just take the existence of dedicated melee troops. They wanted to make melee work in the TT so they made the Fluff work for it (Heavy armor etc.)

You are always free to have your own interpretation of the lore, but if you start to ignore thematic core elements your conclusions might still be valid in your own setting, but they wont fit anymore in the fluff we have.

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.

Ah, now it is getting easier for me to understand you. Though you have to admit that this "flawed approach" is a key-element of the WH40k lore. On one hand we have the Judge Dredd Inspired Mega Cities that even culminate into Hives, on the other hand we have the WH40k "grimdarkness" that tries to create a feeling of humanities struggle to survive. Mankind seeks populations centers for the protection they offer. The theme is around "bastions" or "forts" that offer some kind of protection, a thematic you get in most fiction that is about constant conflict etc.

I agree that this approach is flawed in most sci-fi scenarios where people arrive on new worlds that only seem to have one town but in WH40k it is understandable to some degree. If you think about it most battles in the lore, not the TT, are about sieges. And in most of this battles the defenders, in this case the imperials, would have lost if they had not concentrated their forces around several, defendable strongholds and waited for reinforcements. This tries to catch the atmosphere of the siege of a medieval castle (the entire "gothic" aesthetic aims at that) and this you cant compare to WW2 scenarios.

WH40k has its absurdities but does explain them to a degree. Just take the existence of dedicated melee troops. They wanted to make melee work in the TT so they made the Fluff work for it (Heavy armor etc.)

You are always free to have your own interpretation of the lore, but if you start to ignore thematic core elements your conclusions might still be valid in your own setting, but they wont fit anymore in the fluff we have.

Having written a fortress world for the RPGs, I'm pretty sure they can work even when dealing with a "true" planetary scale, rather than the more common sci-fi "abbreviated" planetary scale. The writeup of Hethgard in The Jericho Reach was a deliberate attempt on my part to write a fortress world where the entire planet was a singular, extended fortification - underground tunnels, subterranean bunkers, a command complex inside an armour-plated mountain, and occasional surface fortresses that allow confrontation of enemy ground troops.

Having written a fortress world for the RPGs, I'm pretty sure they can work even when dealing with a "true" planetary scale, rather than the more common sci-fi "abbreviated" planetary scale.

Well, that is what a Fortress World is made for, to endure any imaginable invasion. But that does not make an invasion with billions of soldiers common in the fluff of WH40k. A prime example for such an Invasion would be the 13th Black Crusade with the invasion of Cadia Prime though another prime example for the necessity of strong bastions is the hive world Armageddon.

Though the Fluff of WH40k is far from being consistent these rather "small" engagements have been the norm for the most of the time. Here and there they had the effort to explain these but in the end it boils down to how they made up their setting. The good thing however is that we can make whatever we want from it. But if we change such major aspects we always have to accept that we are not walking in the planes of the original fluff anymore.

Having written a fortress world for the RPGs, I'm pretty sure they can work even when dealing with a "true" planetary scale, rather than the more common sci-fi "abbreviated" planetary scale.

Well, that is what a Fortress World is made for, to endure any imaginable invasion. But that does not make an invasion with billions of soldiers common in the fluff of WH40k. A prime example for such an Invasion would be the 13th Black Crusade with the invasion of Cadia Prime though another prime example for the necessity of strong bastions is the hive world Armageddon.

Though the Fluff of WH40k is far from being consistent these rather "small" engagements have been the norm for the most of the time. Here and there they had the effort to explain these but in the end it boils down to how they made up their setting. The good thing however is that we can make whatever we want from it. But if we change such major aspects we always have to accept that we are not walking in the planes of the original fluff anymore.

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.

I don't regard scale of conflict as being such a "major aspect" as to essentially invalidate whole swathes of people's ideas. 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; the intro I wrote to the Regiment Creation chapter in Only War works to try and find some middle ground amongst a variety of sources old and new).

A lot of the time, whenever concrete numbers are given to things in 40k, those numbers are flawed. The official write-up of the specifications of the Land Raider gave it fundamentally weaker armour than that of a modern day main battle tank. The masses of starships given in the Rogue Trader line could be interpreted to suggest that those starships were made with a substance less dense than styrofoam. Planetary populations are written that look big on paper but never quite bear up to scrutiny based on the supposed size and population density those worlds are meant to have. Generally speaking, applying concrete numbers to 40k is tricky and rarely works well. It's why it happens so comparatively rarely - vagueness and generalisation are preferred instead. And every time concrete numbers are provided, people latch onto them and extrapolate and infer all sorts of things from them...

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.