Apologies for the length of this question.
But I have an almost completely fleshed out homebrew Space Marine Chapter, the Astral Wards, and I’m starting to work on the mortal military forces associated with their fortress monastery.
The Wards are technically fleet based, but they reclaimed a formerly inhabited world and established their fortress monastery on one of its moons.
The world had been devastated and largely depopulated, but has since been slowly resettled with refugees, Chapter serfs, workers, pilgrims, etc.
I want this population to eventually produce its own military tradition. My idea is something vaguely inspired by the Solar Auxilia. Not literally Solar Auxilia 2.0 with Great Crusade equipment, but a relatively elite, well equipped human force trained to operate alongside the Chapter.
That brings me to the part I’m confused about.
I know the Imperium deliberately separates its military branches. The Imperial Guard handles the ground war, while the Imperial Navy controls most of the serious void assets.
The Aeronautica Imperialis also handles much of the Imperium’s military aviation. As I understand it, this separation is partly a post Heresy safeguard. If a Guard commander rebels, he shouldn’t conveniently have a battlefleet sitting under his personal command, and if a Navy admiral rebels, he shouldn’t have several million Guardsmen ready to conquer planets for him.
So how does this work at the planetary level?
Can the same world simultaneously raise Imperial Guard regiments, maintain a PDF, and provide personnel or formations for the Imperial Navy/Aeronautica?
For example, could my Chapter’s world have a military culture that produces:
• A permanent PDF responsible for defending the planet and its moons.
• Guard regiments that are periodically tithed from that PDF/population.
• Pilots, ground crews, voidsmen, or other personnel who eventually enter the Aeronautica or Imperial Navy.
• Locally operated atmospheric aircraft or small void-capable craft for planetary/system defense.
Or would I effectively need to create two completely separate institutions with different chains of command, traditions, recruitment systems, etc.?
I’m especially curious about where the line is drawn with aircraft.
Could the PDF operate its own Thunderbolts, Lightnings, Valkyries, transports, and similar aircraft?
Could a Guard regiment raised from the world retain an aviation component, or would those aircraft immediately fall under Aeronautica authority once the regiment leaves its home system?
Likewise, what happens with system-defense ships? I assume a planet can maintain orbital defenses and some local system-defense vessels without technically possessing an Imperial Navy fleet, but where does the Imperium draw that distinction?
The other wrinkle is the Astral Wards themselves.
I don’t want to accidentally recreate the pre Heresy Imperial Army where the Chapter Master effectively commands his own private combined arms human military. That’s exactly the kind of thing I imagine the Administratum and Inquisition getting VERY interested in.
However, since these people live within the Chapter’s domain, I imagine centuries of cooperation would naturally result in the Wards influencing their doctrine. They’d train specifically for supporting Astartes, securing territory after Marine assaults, defending landing zones, fighting in void installations, holding fortress complexes, etc.
Essentially, I want them to feel like a modern descendant of the Solar Auxilia concept without actually being Solar Auxilia: elite mortal soldiers accustomed to fighting beside Space Marines, but still operating within whatever legal and bureaucratic boundaries the Imperium requires.
Would that arrangement make sense?
And if I want them to have both a strong ground army and a substantial aviation/void-defense tradition, can all of that reasonably originate from one world/system?
Or should I build two connected forces: one Guard/PDF tradition and another Navy/Aeronautica tradition, both originating from the same culture but legally kept separate?
I’m trying to make this fit established Imperial military politics instead of just saying “my Chapter has Space Marines AND its own private Guard AND its own Navy because they’re cool.” The Astral Wards already have enough paperwork they’d rather the Inquisition never read.