Avernite Army Organization
The forces levied by Avernus in the first wars of expansion, were to set the tone for the organization for the whole of the Avernite Army. Until then, Avernus' forces had followed the standard organization for the Imperial Guard, a regiment forming the primary tactical formation, with any organization beyond that being ad-hoc formations in the field. But even the regiment was a temporary formation, as it would typically receive no further reinforcements once it arrived at the warzone. Given all the regiments of Avernus were incredibly close to their homeworld, the regiments began to acquire permanence, and once the larger battles took place, the role of Avernus in the greater trust was assured. Avernite forces would be the shock troops that would lead attacks while Midgard and Byzantium provided the followup cannon fodder.
But better organization was needed. Ancient tomes on Dark Age military organization gave the basis. The basic unit was the ten man squad, mounted in a Chimera IFV. Five squads made a platoon, and five platoons and a mortar section made a company of some 300 soldiers. Four companies make a battalion of 1,200. Three battalions of infantry and one of artillery with 25 guns make a regiment of 4,800. Avernite regiments, you will notice are much smaller than their Midgardian or Byzantine counterparts, and this is due to the fact that Avernite forces at every level, are trained for breakthrough and assault. But a regiment is not even the main force on the battlefield. The Avernites organized their regiments to act as part of a greater whole, with two mechanized, and one armored regiment forming a mechanized brigade and the reverse being true for armored brigades. An Avernite Mechanized Division would be made up of one armored brigade and two mechanized brigades, thus having four tank regiments and five mechanized regiments. There is only one all arms brigade, and that is the artillery brigade, which controls three regiments of Basilisk Self-Propelled Artillery.
These main combat forces are joined by several specialized battalions dealing with communications, chemical and biological combat, Triple A, enginseers, and reconnaissance. The division, as Avernites call it, is the main tactical formation, and is itself part of the corps, with an armored division and two mechanized divisions forming the main combat force, with a brigade of Valkyrie dropships, three of artillery and an armored Rough Rider regiment forming the support elements. Four of these corps would thus form an Avernite Field Army. Four Field Armies and two Tank Armies would provide the combat forces for an Army Group, along with an Artillery Corps, a Deathstrike Missile Division, an Airborne Corps, a Mechanicus Combat Engineer division and an Avernite Air Force providing the air cover. This is the highest organization of Avernite forces to date, but the coming of the Ork gods may necessitate further growth.
Combat doctrine
The Avernite Army, as has been previously mentioned, is geared towards one thing, breakthrough and assault. Thereby, in the Avernite's mind, defense is to be striven against, as an action that will only aid the enemy. Avernites also share a keen bond of comradeship within their ranks, a trait carried over from Avernite civilization itself. Thusly, Avernite Sergeants tend to act as second fathers to their troops, with whom they train from the moment they enter the army. It also means that when fighting any species and taking casualties, the loss of their leader or fellow soldiers is keenly felt and often evolves into a hatred for any they are fighting against. This close bond is compounded by a near suicidal bravery in the ranks, a natural development of the Imperial Truth being indoctrinated into every Avernite soldier, from Marshal down to buck Private, so every soldier knows that humans are nobler and purer than all others, and that other races, are not merely despicable, but actively malign, and that compassion is to be striven against as a crime against humanity (There are, it is true, exceptions).
This devotion to the advance pervades all aspects of Avernite military thought. For example, if a major has three companies in action, one of which is slowly advancing, one that is stalemated and one that is being forced back, and he has three tank companies, and three batteries of artillery for support, there is only one place they can be sent to. The company that is advancing. Avernite forces have always been outnumbered, and drawn out conflict is something to be avoided, so if there is one place that an advance is being made, then all forces at every level are to be deployed to that area.
Will probably change later.