VBS / Arma2

The Virtual Battlefield System, or VBS, is a tool used by the United States Marine Corps for combat training. It utilizes networked computers to create a full-scale virtual battlefield, wherein hundreds of Marines can train both in force-on-force scenarios and versus large groups of A.I. opponents. It is an invaluable tool for teaching the value of teamwork and communication in battle, before the real bullets start to fly.

Arma2 is the civilian-ized version of that system. It's the same exact tool, just with the classified bits removed. How realistic is it? Well, go watch this group of veterans demonstrate it. You're riding along with a Marine company XO in his LAV25 as he coordinates the advance of a platoon of Abrams tanks down a rail line. They soon encounter a reinforced Russian mechanized company deployed for an in-depth defense.

The video highlights the close coordination and disciplined comm procedures required to make a modern American military unit effective. This is how it's done. The first four minutes of the video consist of the frag order and mount up, so you can skip that bit if you're the impatient type.

EDIT: Here's the same battle, from the perspective of the infantry company assaulting the town to the south.

You can try Arma2 for free here. If nothing else, you can have fun trying out the hundreds of different weapons and systems, all of which are simulated in extraordinary detail, from the M9 to the M1A2.