Intro
Planetary invasions were once considered a thing of the past. With the combination of nuclear weapons and pinpoint orbital bombardments, simple orbital supremacy became more than enough to cow a planet into submission. Armies became simple police forces, meant only to keep conquered worlds in line. However, that all changed with the introduction of the entropy field.
Out of all of humanity’s inventions, almost none have changed warfare as much as the entropy field. It is an advancement of the metaspace engines used for faster than light travel, but for planets. It is a device that interacts with a planet’s gravity well and atmosphere. A combination of the technological and sorcerous, it shunts any release of energy above a certain threshold into the Aether, making the release harmless. In practicality, this means that nuclear weapons, and capital-ship grade, city destroying levels of orbital bombardment. Battles had to be fought again with soldiers and tanks on the ground to at least take the entropy fields generators or the power stations that supply them. Mere orbital supremacy was no longer enough.
Planetary invasion doctrine had to be worked from the ground up to what it is in modern times. Four stages were constructed to run a successful planetary invasion.
Stage 1:
Complete orbital supremacy, or partial orbital control over the drop point is established. Dozens of Orbital Drop Vehicles(ODVs) are then launched from the transport ships. These will form the bones of the invasion. ODVs fall at high speed towards the drop point, meant to bypass anti-air defenses the best they can. They are launched in a ring pattern around the future staging grounds. Each ODV carries about fifty troops, including carapace power armor forces. The ODVs come equipped with supporting firepower for the troops, along with heavy and light point defense as their main armament.
The ODVs job is to establish a “column” of protected airspace for the next stage of the invasion. While they would not be able to fend off a concentrated push on their own, the speed of the drop will hopefully prevent any true attack from occurring until reinforcements can arrive from above. But the weapons and troops provided by the ODVs can defend against isolated skirmishes. And if there are concerns of immediate retaliation on a hot drop point, the ODVs can always be loaded with a greater concentration of metaphysicals. However, commanders often loathe risking such a precious resource on the dangerous drops. The only common concern such a drop would have, is a prepared golem cadre. These jet-powered 18ft tall mechs could reach a landing spot in time and completely destroy the operation. This phase can last as little as thirty minutes.
Stage 2:
Once a landing perimeter has been established, the next stage can begin. Frigates are launched from their motherships and descend to the skies above the drop points. These vessels are the largest spacecraft which can operate in atmosphere, with the largest being capped out at 500m in length. These vessels fulfill three roles, the first is to flood the skies with strikecraft from their hangar bays, land heavy ground forces, and support the invasion with their mag-cannons, purposely kept weaker so as to not be caught by the planet’s entropy field.
If things go according to plan, then thousands of troops, vehicles, and supporting logistics will be brought down to secure the drop point. This first push by the attackers is incredibly important, as the initial landing will only hold a fraction of the invasion force above, which will be brought down in stage three by frigates designed purely for transport, without combat in mind. It is up for this beachhead to secure the landing zone and the airspace above from the inevitable counterattack. The defenders of the planet will want to crush the invasion at this juncture as soon as possible. This is because initial drop points are often placed near the space elevators of a planet. Once a space elevator is claimed by the attackers, they can easily ferry down the rest of the armies in record time. At most the second stage will take one to two days.
Stage 3:
If the beachhead is not crushed, the invasion can progress into the next stage. The purpose of this stage is to ferry down enough of a force to take a nearby space elevator. The attackers must play a delicate balancing act at this phase. If they move too soon, then the likely heavily fortified city, where the elevator is located may repel them. But wait too long and the larger defending armies will mobilize and crush the attackers. Defending forces cannot possibly cover the entire planet, and troops must be dedicated to defending the entropy field generators at all times. If the attackers secure control over them, then the invading army can turn them off, opening up the entire planet to orbital bombardment. The entropy field generators are the prize of the whole operation. Most defending armies will simply surrender if they are taken. The other option being completely deleted from orbit.
Once the attacking army is brought down, high-speed and high-strength forces such as golems and powerful metaphysicals will be sent to attack weak points and key infrastructure targets, playing havoc with the defenses.
The openings provided by these undermining efforts will hopefully prove enough for the attackers to take a space elevator. If they successfully do so, then the invasion can progress to stage four. Stage three can last several weeks if not months.
Stage 4:
With the successful capture of one or multiple space elevators, then the invasion can begin in earnest. Millions of troops and their supporting vehicles will be brought down in mass. Here the attacking armies will coordinate and move to take the planet’s entropy field generators. Large scale battles will occur either at the defensive positions around the generators, or where the defenders try to retake the space elevators. Though that is more of a question of how strong the defenders are. If they are weaker, then they will most likely fall back and stall for time until naval reinforcements can arrive. If not, then most battles will take place around the space elevators, grinding each other down until one side comes out on top.
This stage can potentially last for years, depending on how self-sufficient the defending planet is. But one thing is for certain, millions will die in the name of their gods.