Lord General Potemkin is the commander in chief of Imperial Guard forces assigned to Driftward Command in the Obscura Sector. His task basically revolves around the raising and assigning of IG regiments. By arrangement, regiments raised in one of the four ‘directional commands' are deployed elsewhere in the sector, if not further afield. Regiments raised by Driftward Command are offered over to other commands and other Lords Militants in other sectors. Careful count is kept to ensure that men out is balanced by men in, that for every elite or armoured unit that leaves, another is received from outside of the Driftward Strategic Area of Responsibility.
The Lords Militant of the Obscura Sector divide their bailiwick into four; Spinward, Driftwards, Coreward and Trailing. Each of these ‘Commands’ within the Sector has a nominal four armies with which to prosecute the emperor’s wars. Of course these are only administrative ‘armies’ for accounting purposes. Each will tend to have a flavor; a slant towards the origins of the Generals assigned to lead it on campaign. Lord General Potemkin favours Vostroyan and Valhallan Generals in the 15th Army.
Driftward Command has four 'armies' at it's disposal. These are actually the logistic tails that enable campaigns to be prosecuted. In theory an 'army command' can fight multiple campaigns simultaneously, this actually depends on the logicistic Main Supply Route being linier enough for this to be feasible enough to allow this to happen. The 15th Army contains a number (up to 700) of Corps. It is these administrative groups that attach and detach regiments to form formations that are then deployed. It is these Corps that are the umbrella organisations for the formations that actually do the fighting.
The scribes of the Lords Militant keep the numbers and the lists of what unit is a part of which formation. Everything about what is sent to support that regiment or formation in the field is recorded. Thus it looks like every IG regiment is well supported and gets all the material it could wish for. Of course, occasionally, data on the amount of material that the regiments actually received comes back to the Lords Militant’s offices. The disjoin here is that it normally goes into the Departmento Ante Bellum, into the records. The Departmento Ultra Bellum, who deal with planning and future wars, rarely refer to the records to inform their planning, it’s a different office within the Departmento Munitorium.
Still based on Agripinna, The Klestor Sub Sector war office deals with far more than the Klestor Sub Sector. There was once a conflict there that spanned five systems and involved the Inquisition, Imperial Navy and Adeptus Astartes. The expertise gained has not been completely eroded by time. So the Klestor Sub Sector war office is pre-eminent within Driftward Command. It is here that wars are planned, at least as far as which assets are to be assigned.
The 72nd Army Corps was the number of the Skitari and Astartes supported Army Corps that deployed to Devos IV hundreds of years ago. This number was reassigned to the Devos IV expeditionary force by the Departmento’s bureaucrats, possibly at the behest of a Staff Officer who is also a student of military history. Most of the Devos IV PDF regiments trace their origins back to elements of the 72nd Army Corps of antiquity.
The Vostroyan doctrine for campaigning is for Brigades of 1 to 4 battalions as the normal unit of maneuver. 1 to 5 Bdes form what the Vostroyan's refer to as a 'Battle Group'. General Tolstoy's staff has for the last seven years referred to itself as the 17th Battle Group. This number stretches back to a brief and successful campaign putting down a rebellion based around promethium manufacture on the Ice world of Stegen. The Departmento has not changed the number yet.
The 15th Army has assigned numbers 900 to 904 for the 72nd Army Corps' brigades. The 17th Battle Group believe this to be optimistic in the extreme. The available assets, from Armageddon, Krieg and Valhalla, amount to one Division. The Vostroyans do not use 'Brigade' in their vocabulary and therefore the Brigades are Divisions. They have nominally assigned another Division for any remnants of loyalist PDF units. This includes the Cadian 144th Long Range Recce Regt, sent to secure the Priory of the Silver Chalice when the insurrection began and a detachment of the Praetorian 5th, who were guarding the system defences on Devos XII.
In the unlikely event that the IG force on Devos IV eventually exceeds five brigade/divisions, another 'Battle Group' would be needed. This new Battle Group would still be a part of the 72nd Army Corps.
Another Vostroyan, General 1st class Zhukov, has seniority over General 2nd class Tolstoy. General Zhukov has Lord General Potemkin’s confidence. Gen Tolstoy has commanded 17th Battle Group for the last three years, having been a Regimental CO within 17BG prior to that. Gen Tolstoy will only get "his" command back if either General Zhukov is killed or the camapign goes on for so long (or goes so badly) that 72AG gains another Battle Group; elevating Zhukov back out of his way.
So, therefore; Imperial Guard forces both en route to Devos IV and those already present all fall under the umberella of the 72nd Army Group. (Although those already present won’t know this until the main body arrive).
The HQ of the 72nd Army Group continues to refer to itself as 17th Battle Group, because the Departmento Munitorum has not officially renumbered it yet. The chances of a second ‘Battle Group’ within the 72AG coming into existence are thought to be remote, but the possibility remains.
The fighting formations of the 72AG are:
900 Inf Bde
901 Inf Bde
902 Inf Bde
903 Inf Bde
904 Inf Bde
Although their HQ, 17BG refers to these formation as “Divisions” because they (the staff officers) are Vostroyan.
902 Inf Bde is comprised of the existing assets that Gen Tolstoy knows are en route; ASL, DKK and Valhallans. It is mostly Armd (the ASL) and Mech (the DKK). If the Navy’s 50th Tactical Lift Wing can be persuaded to ‘hop’ the Valhallans in theatre, then so much the better.
903 Inf Bde comprises of the remnants of the Preatorian 5th who were the garrison for the system defences on the Moon of Devos XII, the Cadian 144th LRRR, who were sent to bolster the Loyalists and any remaining Devos IV PDF who remain within the emperor’s light.