That is a TOC, or Tactical Operations Center. It is an operational headquarters - in this case (as I have heard it) the headquarters for a brigade of the 3rd Infantry Division. Something like this would consist of several tents and/or headquarters vehicles that are temporarily co-located to provide a command and control center. They move frequently (depending on the tactical situation). Most Brigades that I am aware of would have more than one TOC in operation (usually a forward and a rear) so that one can move while the other runs the battle. The soldiers at the TOC would usually consist of the Brigade staff and, if the commander was not physically present, would be run by the operations officer.