From Corporate Shadowfiles:
- Ares: Light Regiment
- Aztechnology: Regiment or larger
- Fuchi: Company
- MCT: Company
- S-K: Batallion
Big enough to be effective, small enough to be cost effective. 
And secret enough that you'll probably never know. That secretary pool over there? Yeah, SpecOps team. Those freighter crews? Navy crewmen for Subs that are hidden away. Those cargo pilots? Fighter pilots who practice in Sim while the cargo plane is on autopilot.
Yes and no. Consider Yamatetsu/Evo; how big is a Carrier Strike Group? Quoting from that
paragon of information ...
A carrier strike group (CSG) is an operational formation of the United States Navy. It is composed of roughly 7,500 personnel, an aircraft carrier, at least one cruiser, a destroyer squadron of at least two destroyers and/or frigates,[1] and a carrier air wing of 65 to 70 aircraft. A carrier strike group also, on occasion, includes submarines, attached logistics ships and a supply ship.
7500 people, with more being possible. That's regiment-plus level -- and I can't imagine one of the ten largest powerhouses in the world having that minimal amount of force projection for its shipping, &c. To give you an idea, the current (late 2011) total personnel count in the US Armed Forces -- second largest in the world -- is 2¼ million people. A lot of those are in support positions; I vaguely remember one comment that said it took 20 support people to keep one soldier in the field. Using that as a benchmark -- and yes, that could be completely wrong -- that'd be 107,000 people on the field/seas/air. No, the corps aren't going to have that size, but consider the Balkanization the world has undergone, and the amount of power the corporations represent -- and thus what they have to protect.
I grant you that Aztechnology is probably going to have the largest standing army among the corps, just because a) it's always at war, and b) it has Aztlan's armed forces to draw from and trade into, but I think -- have always thought -- that the military sizes in the 'Corporate' books were massive underestimations. 5,000 men to put into the field against someone in SE Asia who's doing some Very Bad Things to you and who has 15,000? Can you imagine Fuchi or MCT having only
250 soldiers??
Yes, they have security forces. Yes, in a pinch, they can always pull from the one in 200 corporate citizens who wear a badge and carry a gun. Yes, they can hire mercenaries -- but now you're dealing with the size of the merc outfits. (Fortunately for my peace of mind, the SR writers tend to view mercs the way David Drake does -- and the way I like to think of them.) How
big is MET2000, or Tsunami, or 10,000 Daggers, or Combat, Inc? How big is, say, Picador's unit? You can bet that
she's coming to the party with everything she has ... but is that anything over 150 people? That's good for protecting a couple of villages or a small town, but your corporation has a
lot more at stake than that ...
Consider also the fact that all of the Big 10 -- with the possible exception of Horizon -- are
nuclear powers. Ares and SK (at the very least) utilize terminal reentry weapons, i.e. Thor shots. Both of these weapons are purely military in use (so yes, you could consider Danchekker having been taken out in a military operation), and I just can't see a corporation with at most 1500 people under military arms as being capable of dropping the hammer like that.
Last, remember the Ensenada Strike -- the Corporate Court pulled from
all the other AAA militaries. I again can't imagine Fuchi saying, 'Uhhh, sure, you can have
half our military for this...'
I don't know. I'd personally put the total personnel in all branches of the corporate militaries to be in at least the tens of thousands each, up to 75-100k. If Aztechnology has the biggest at 175k+, then a 'big force' corporation such as Ares or Saeder-Krupp should have 100k, while a 'small force' such as Evo or Horizon should probably run 50k or so. Again, that's among all the branches -- but if you functionally restrict that to two sections, Navy and Marines, each of whom have air support and at least one of which feels no restriction in going 3000km away from the nearest seashore, you have some pretty hefty forces.
