Also want to make some notes on cuts to the AFFS prior to this time. Irose gleaned that the Suns fielded 125 Mech regiments prior to the formation of the Star League. This would mean 37 such regiments were disappeared prior to the start of the Reunification War
There is a lot of detail on these changes on Page 32-33 of H:RW. H:RW specifically mentions that 37 regiments were transferred to the SLDF. It also describes the regiments as:
Alexander Davion took the opportunity to prune the most troublesome, worst-trained and worst-equipped units from his military.
The Terran and Outworld Brigades that were likely successor formations probably patrolled their defunct Marches until they got shipped out for foreign service. Never fully trusted these border guards performed a vital task screening the Federation’s frontiers. Their totals were most likely more then 6 regiments a piece as both entire groups were sent packing to the SLDF.
Again the Terran Brigade is specifically mentioned as being transferred to the SLDF.
From H:RW
The once-proud Terran Brigade—a large organization of regiments that had guarded the former Terran March and still harbored deep resentment against Davion for his eradication of the Terran March principality—was transferred whole
Based on that I would actually put the Terran Brigade at 12-18 regiments- roughly on par with the Syrtis Fusiliers, but less then the Avalon Hussars. I would put the Outworlds Brigade at about 6 regiments. (and for that matter I would put the Draconis Brigade at about 6-8 regiments. we'll get back to this in a little bit)
Training Cadres were the next likely group shipped off to the SLDF or folded into other AFFS local units. The Albion was the largest such formation but its incorporation into the Star League Academy system means its Cadre would be absorbed at this time. Other Federation Military Academies could have incorporated their Cadres into Regional Defense Commands bolstering those units and eliminating the need to account for “second line assetsâ€. Not sure if their total number would add up to a total of 6 Mech regiments but it might be close.
I think you are over doing the size of the Cadres- I think only Albion had a large formation at this point.
Independent Commands, aka as a number of private regiments, who no doubt supported Alexander during the Civil War probably left for SLDF service. Encouraged by generous offers of upgrades the First Lord would be wise to add these skilled units to his new army. Again I’m not sure if their total number would add up to a total of 6 Mech regiments but it might be close.
Again covered in H:RW- it says a number of former private regiments were transferred to the SLDF- I don't think they were given a choice or went voluntarily.
Not sure if half of the Syrtis Fusiliers joined the SLDF but I could think of a reason why. Some folks in these units probably still aren’t trusted by Alexander and this is a good way to weed out the undesirables. If the total number is half then 6 regiments is a good number for the Fusiliers to sacrifice at this time.
H:RW is specific that it was half of the Syrtis Fusiliers. So I would say 8 regiments.
Finally the Avalon Hussars who make up the bulk of the AFFS would likely be asked to join the SLDF at this time. No doubt some would accept such an offer but 6 regiments could be a little too much to ask here.
Based on the description of the types of regiments that Alexander Davion gave to the SLDF I doubt there would be many Avalon Hussar regiments transferred- probably only the dregs if any.
So I would say we have the following
16 regiments of the Terran Brigade (all but the unit that became the Clovis Guards)
8 regiments of Syrtis Fusilers
3 regiments Albion Cadre
8 independent regiments
2 Avalon Hussars
But wait you say- what about the Outworlds Brigade and the Draconis Brigade? Well I suspect the Draconis Brigade is very small following the Civil War- I suspect they were small to start with and then they got the crap beat out of them in the civil war as they supported Laura Davion. (Don't think there was a Draconis Brigade? It is indirectly mentioned in H:RW- "He [Alexander Davion] dismantled the structure of five equal principalities and in its place organized the Federated Suns into three marches, in the process combining the five disparate military organizations into a single united AFFS." and "Gone were the five principalities and their virtual private armies." We definitely have the Avalon Hussars, Terran Brigade & Syrtis Fusiliers, so the other 2 must be the militaries of the Outworlds and Draconis marches. )
But I don't show them being transferred to the SLDF- instead what I think we need to do for SD is have these units become the core of the regional forces for the Draconis March and the Periphery areas of the Crucis March. What I see happening is that rather then having regiments join the RDCs as whole units, they instead were disbanded and the soldiers returned to their home regions where many were recruited to join the newly forming RDCs. (this way we can mention this in the intro to the RDCs and not have to rewrite all of the units. )
I still think the idea of having both RDCs and March Militias is valid- what I might emphasis more is that the March Militias are under command of the military leader of the March, while the RDCs are under the command of the Combat Region leader. The RDCs are more of a tactical unit, while the March Militias are a strategic reserve for the military commander of the March.