Careful, notice how we don't know there entire military forces just yet, just what our recently emplaced spies know. Since it was after all during this timeframe when they started making efforts to upscale their military, and with the ORDI next door it wouldn't surprise me if they hired every merc/pirate they could and raises for legio in an emergency (or already started increasing their military sooner on the timeline since major butterfly's). They got the money to so from their trade links with the FWL.
It appears that we achieved strategic surprise. They're acting unprepared. I wouldn't be surprised if they are somewhat able to call in mercenaries and stand up militia, but the major advantage of doing this now is that there just aren't that many mercenary companies available for hire-- the Great Houses will have snapped up almost anyone willing to fight in a seriousface war. There might be some merc/pirate outfits hanging around, maybe some low quality lances, but they're either going to be unwilling to fight a serious war against serious opposition or will be chaff. We've penetrated their counterintelligence people and have some idea of what's going on; I suspect that if they had large quantities of mercs or had been rapidly beefing up their own forces we would have caught wind of it. The only thing that seems to be going on is "panic."
If the FWL wasn't getting smashed by the Lyrans and vice versa I might expect them to make threatening noises or deployments in our direction via establishing a tripwire on Alphard, or even use their deeper pockets to deploy mercs in support of their germanium suppliers. But I don't think the cavalry is coming for the slavers. The Marians produce low-tech, low-quality weapons in the periphery, I'm not really worried about their ability to rapidly stand up forces capable of fighting us.
Remember that the ORDI order of battle is:
15 Combined Arms Regiments (Helghan)
2 Battlemech Regiments (Helghan)
2 Mercenary Battalions (Helghan)
1 Mech Regiment (MoC)
2 Armor Regiments (MoC)
3 Infantry Regiments (MoC)
1 Mech Regiment, Mercenary (Taurians)
1 Mercenary Mech Company, 1 Elite Mech Battalion (Aurigans)
This adds up to somewhere around 4.5 regiments of battlemechs and almost 21 regiments of armor, infantry, or combined arms (and our combined arms is 10% powered armor, remember). We're also bringing 3 Hastas and 6 Damascus, which is 756 ASF for complete aerospace dominance. They're digging in with 4 battalions of mechs and the local defenders. In mechs alone we outnumber them probably... mmm... 3:1, let alone all the other stuff. And since we have complete aerospace dominance, we can lock down an entire area of operations, mulch the defenders and defeat them in detail, then leapfrog onto the next area of operations to defeat THEM in detail.
This isn't to say that the Marians *can't* hurt us. They can. But I really doubt this is going to end more than one way.
