Here's my take. I see the Imperial Army as technically being all ground forces, but actually being mostly a small cadre force that can back up local forces with officers and NCOs, and a few field units to act a local reserve for the local armies (and deter rebellion). I think that's kind of implied in the original Bk1 CG system, where you only have to roll a 5+ to get a commission (compared to 9+ for the Marines). That implies to me a force that has a lot of officers.
From my IMTU write up:
The Army theoretically comprises all terrestrial forces, and includes Nautical Forces Command (the “wet” Navy) and the Close Orbit and Atmospheric Command (flyers), in addition to Ground Forces Command. In practice, the Imperial Army itself does not maintain those forces, but leaves them to the local planetary governments. The Imperial Army is primarily a cadre force that trains ground Officers and NCOs to support local planetary Armies, and provide High Tech Level reserve forces that can be moved relatively quickly in the event of direct intervention or foreign invasion. The standing units of the Imperial Army serve as a training ground, with officers and young soldiers starting in them to learn leadership and tactics, then being posted to local Armies that are involved in or preparing for military conflicts to build combat experience.
Individual worlds are required to maintain standing and reserve forces based on the threat to the system from foreign enemies. In many cases, the local government will maintain larger forces for domestic political reasons. Any local government may request Imperial forces or personnel to augment their forces. Local wars and counter insurgency operations provide a valuable and regular training ground for the Imperial Army’s professional leadership, and the occasional opportunity to deploy regular army units as well. Local military forces will almost never be deployed out of system, but local soldiers may be integrated into Imperial Army units in the event of a major mobilization.
As a general rule, the Imperial Army will maintain a regular force capable of defeating the single largest planetary army in a subsector to ensure that it can put down any local rebellion successfully. Imperial Army units will always be at least one and preferably at least two Tech Levels above the best local army in the border regions.
The main tactical organization for the IA is the Combined Arms Brigade. Each brigade is capable of independent action, or can be combined with other brigades to from larger formations. Divisions are common, but Corps are not, and Field Armies are rare. Training units are Branch “pure” Regiments.
In determining the size of a local Imperial Army garrison, the Army will determine the size of the largest local army and then determine the proper combination of tech level and force size needed to defeat it with Imperial “Space Superiority”. This will normally be a one to one troop ratio reduced by one organizational level for each tech level advantage. For example, Jewell has a local army consisting of a TL12 Grav Cavalry Corps. The Imperial garrison would be one TL 13 Division, or one TL 14 Brigade of the same troop type.
There are four basic types of formations in the Imperial Army:
Field: Full strength tactical units capable of immediate combat operations.
Training: School Regiments that train civilians or Local Army personnel to serve in the Imperial Army. They provide minimum combat power themselves, but are critical to the manning of the IA.
Cadre: Full strength Headquarters and full compliments of equipment with small numbers of soldiers to perform maintenance. Designed to absorb large numbers of trained soldiers from training units or local armies in the event of mobilization.
AG: Augmentation Groups are ad-hoc formations tailored to the requirements of a local government’s military situation. They provide assistance to local armies on request.
Household Troops
Nobles are allowed to raise household troops. These forces are usually small and intended for the security of the Noble, their family, and valuable household property. In the case of high ranking nobles, these forces may be very large and significant. Most Dukes have a force large enough to deal with minor rebellions within their sub-sector (much better to deal with it quietly without having to bother the imperial admirals and marshals). Household troop will normally be veterans of other services as few nobles have the wealth to establish a permanent training base of their own.
Local Armies
The Imperial Army gives wide latitude to local governments in organizing and equipping their forces provided they meet the force minimums set by the Imperial Ministry of War. The general pattern that emerges is one of large standing forces closer to the borders diminishing to cadres and reserves in the core of the Imperium. Organization, uniforms, and doctrine of local armies are heavily influenced by local cultures and terrain.
Mercenaries
Since full scale Imperial Army intervention usually results in the replacement of local security officials and military officers with Imperial personnel, local governments are reluctant to call on the Imperial Army until the survival of the regime itself is threatened. To fill the gap between the need for outside military forces and the imperative for Imperial Army intervention a large number of Mercenary organizations have developed. The Imperium accepts and licenses these organizations, provided they to not operate against Imperial forces and abide by the Imperial Rules of War.
Just my take...
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). A system might be responsible for providing x number of battalions (corps level for pop 10 or larger), Barons might be held to providing a battalion, a Count a division, a Duke a corps, and so on in that manner.
