I have no doubt that in frontier sectors like the Spinward Marches the Imperial Army is a small force that needs to be bolstered by mercenaries and colonial armies drafted into Imperial Service by treaty obligation.
Agreed
The bulk of the Imperial Army, like the bulk of the IN reaction BatRons, are not stationed in the frontier sectors but are closer to the core sectors so they can be deployed either to the frontier as needed.
I also have no doubt that CT sources point to their being an organised regular Imperial Army.
I fully disagree in that. IMHO there's no point of keeping those large reserves in the depots (that are after all Naval facilities, not Army), and moving them long distances would be quite expensive (mostly in CT, where low berth is not an option).
This strategy has sense in fleet, that takes quite long to build and have their own mobility, but armies, you have them anywhere, don't have their own mobility and are quite less time demanding to organize.
Since you send Word from Regina to the Core that you need help, Word would be received in Depot/corridor about 10-14 weeks after it is sent, Vland about 20-24 weeks, and Capital about 28-34 weeks. Since then, reingorcements will take about the same time, so forst reinforcements from Depot Corridor will reach Regina about 6-8 months after word is sent, from Vland about a year, and from Capital about 15-18 months.
While you cannot build a single battle ship in this time, how many troops can you mobilize?
And imagine what represents to move a full army. while moving a fleet involves qute a lot of people (the crews and marines), they are prople accostumated to living in a ship.
Ground troops, aside from being quite more people (if we asume the 500 battalions an army is said in FFW/IE, at about 600 men per battalion, we're talking tabout moving about 300000 people, plus equipment). Just life support means about Mcr 600 per two weeks of travel. And those 300000 men are confined in close quarters (the ships) they are likely not accostumed to, needing some R&R probably more often than the fleet crews (and imagine those 300000 troops coming for R&R to a downtown...).
My opinion is that the Imperial Army is just the support and special duty units to be bolstered by local armies (probably units already so earmarked and trained and equiped), and kept as close to the posible front as posible (though not in the first border line), probably at sector level.
That seems reasonable to me, especially since a TL15 multi-billion pop Core World planet going traitor/rogue is an entirely different proposition to handle then a TL10 10 million balkanized world frontier mess.
We don't normally see THE Imperial Army because only a proportion of it would shift frontierward, and a large percentage of it MUST stay behind as the real taxbase of the Imperium cannot be risked, EVER.
Another reason why the IN cannot be nuking wayward planets, even given whatever salutary terror/examples may be made- don't be killing what pays the salary.
But even this TL15 multi-billion pop Core World can be contained by the Navy if it becomes rogue while Ground troops are assembled/mobilized. it rebellion would not be critical to the Imperium as lon gas it does not spread (and, again, that's IN's task to avoid, not Army's.
And any rebellion(going rogue planet is probably more easy to occur in the frontier than in the Core, where any planet feels (probably) more Imperial loayalty (even if only due to not knowing anything else), knows that it ahs no outside support and is (again probably) in a more stable zone.
And think what would the Core pople, that to a point they feel secure and Imeprium Loyal, of having to maintain such an enormous aremy where it is not expected to be used (except maybe against themselves, as you say). Will they see it as a good way to expend the taxes?
Anothre point is that, unlike the Navy, that mostly stays in orbit, the Army units have to interact more closely with local population, so knowing something about it is a true bonues. And that cannot be achieved from a year distance, it must be closer.
And after all, Army is an offensive tool (unlike the Fleet, that has also a defensive role. Ground troops can defend the planets only in a limited way. If the enemy obtains Space supremacy and has (relatively) unlimited time, Ground units are useless. Army is to take/recover planets when you are at offensive in a (again relative) hurry and decide to invade them.
It's (again IMHO) akin of the Pacific War, when ground troops could not really hold the islands/atolls if the fleet was taken away. And even if they did, their positions could just be bypassed and left for latter (with the plus that in Traveller those baypassed points cannot even act as recon bases for the main force).
So, Imperium does not need a strong Standing Army, just the core needed to mobilize it with reservists and imperialized units in a relatively short time (I'd say from 6 months to a year). And, again, that's cheaper to do relatively close to wher you expect the battle lines (though not close enough to be overrun in the initial attack) than in the Core.
