You have to first download the Military Analyst extension first, and then active it from Customize > Extensions. Additionally, you have to add the Military Analyst toolbox in ArcToolbox or access the toolbar from Customize > Toolbars.
Open ArcToolbox
Right click on the white area and click Add Toolbox...
Navigate to C:\Program Files\ArcGIS\Desktop10.0\ArcToolbox\Toolboxes
Choose Military Analyst Tools.tbx