From the SRD:
Tactics:Techniques and strategies for disposing and maneuvering forces in combat.
I'm guessing this means that a successful check would cover current military procedures covering both troop deployment, standard tactics in specific situations (ie tankbusting techniques, urban combat maneouvers, etc), and even things like marching order. Obviously, how much information gained from one check would depend on the GM, the complexity/obscurity of the information/knowledge wanted, and any other situational circumstances.
If you're after what synergy bonus five ranks in Knowledge (Tactics) would apply in situations... I'd probably allow it for investigating a battlefield, or possibly in determining if a professional/military unit has any involvement in a scene. I'd probably also allow a synergy bonus to skill checks such as Search/Spot (if you're actually looking for signs of military activity), Profession (if you need to prove that you were a certain rank in the military), and possibly also with Computer Use checks or Drive checks (when performing certain tasks with those skills)
Anyone else care to add to this? Its been a while since I last ran a d20 Modern campaign, so I'm not really in the right brain space (and I've still to write a d20 Future campaign)
