Example: Combat Drop
Grand Strategy
Imperium grand strategy focuses on one goal: expand the Imperium. Since you have to hold what you have to add to it, the Imperium is also concerned with defending and maintaining currently held worlds. This strategic goal of expansion is a major reason why the Imperium continues to support exploration.
When faced with a new alien race, the Imperium will ascertain the race's strength, and determine if it is strong enough to conquer them, or if it must buy time to build up strength. Peaceful coexistence is out of the question; one is inside the Imperium or soon will be. A major race will provoke a major buildup of Imperial forces, including reserves and core system forces. When the Imperium High Command feels they have overwhelming superiority, they will attack. The aim is conquest; enemy systems will be systematically attacked, reduced, and garrisoned.
Strategy
Each sector is considered a strategic unit. The sector's commanding general works with the sector's military AI as the primary strategic body. They assign missions to the divisions, corps, armies and fleets within the sector. One world in the sector will be designated a 'garrison world' where ground forces units can train, rebuild their strength, or have new units brought up. Likewise, a world is designated as a 'shipyard', with a Class V port, where naval forces can rebuild, refit, and rest.
A rebellion on a single world is a sector issue. The Imperium is not to be bothered with rebellions until they cause armed unrest on more than half a sector's planets, or unless the sector's ground forces meet with a serious reverse. Once a rebellion does arise, the sector command assesses its strength and assigns forces to deal with it. Very common, these are overwhelming forces. For a rebellious province or continent on a single planet, a division is sent in. If most of the planet is in rebellion, a corps is sent. The only time an entire army deploys on a single planet is to conquer a major stronghold of a highly-advanced enemy.
Most divisions spend the majority of their time on the garrison world, training. They don't board ship until an alert comes about a potential problem. During training is when combat assignments are practiced; a combat drop zone is a bad idea to make friends with somebody you've never met before on your side. While brigade assignments are flexible, any changes usually happen back on the garrison planet, where the new units have time to work together.
The same cannot be said of space forces. Most cruisers, destroyers and frigates spend most of their time patrolling, looking for smugglers, pirates, and rebel ships. Some destroyers and frigates are tied down at the shipyard as escorts for the big ships, but in most cases patrolling ships are called in to reinforce a group at its destination.
In case of major wars, the relevant sector commands are heavily reinforced, both in terms of troops and in terms of command personnel. The first priority is to stop any enemy preemptive strikes, and then to carry the fight to the enemy. In order to maintain a defense in depth, not all ground troops are committed to the first invasions; rather, some front-line units stay back to defend the nearest Imperium systems, while others carry out the first attacks. Once the first attacks are successful, the former attackers go to garrison on the planets they captures, while the defending troops are brought forward and attack the next series of planets. Hostile shipyards and garrison worlds are preferred targets and are attacked by heavier-than-normal forces.
Operational
Imperium operations focus on the campaign to secure a particular planet. In most cases, a corps or division is assigned to this mission; only heavily defended planets draw the attention of a full army. Ground force commanders draw up a set of critical objectives at the start of a mission, and rarely vary them. One objective is always the destruction of organized enemy resistance in the field, but this is seldom the primary or only objective going in. Rather, enemy formations, starports and manufacturing facilities are primary targets, with final destruction of enemy field forces coming afterwards.
In order to destroy broken enemy forces, Ground Force units establish small bases, called 'firebases', in hostile territory for a battalion task force to operate out of. The forces in the firebase patrol the surrounding territory, tracking and engaging enemy forces found therein. Special Forces are often assigned to these firebases as highly skilled patrollers and trackers.
Tactics
Imperium forces usually have technical superiority over their opponents, but are outnumbered. In order to combat this, they use coordination, mobility and firepower. Coordination allows units to respond quickly to changes in battle conditions; a broken or exposed flank, reinforcements for one side or the other, etc. Imperium units will, in most cases, recognize and respond to these changes faster than their opponents. Mobility is contained in the Imperium's grav vehicles. Without Broadswords, an Imperium unit can move up to two hundred miles per hour across any terrain. While power armor and infantry aren't that maneuverable, their Stallion IFVs are. This mobility allows Imperium units to get places their opponents aren't expecting them, and to get there with substantial firepower. Firepower is a basis of Imperial units from the fusion guns and brilliant missiles in every fireteam to the blaster rifles that Dragoons and Broadswords carry to the heavy missiles that the Broadsword uses as fire support. Firepower allows Imperial units to maneuver freely, since the enemy is more worried about staying alive with all of that energy flying around. With their thermal superconducting armor, Imperium forces are resistant to their own weapons; a significant advantages, since most rebels are armed with old Imperium hardware. While Gauss guns ignore thermal superconductive armor, the Imperium doesn't use them for fear of them falling into rebel hands. Besides, if the rebels don't have the special armor, why bother?