The term theater of operations was defined in the US Army field manuals as the land and sea areas to be invaded or defended, including areas necessary for administrative activities incident to the military operations. In accordance with the experience of World War I, it was usually conceived of as a large land mass over which continuous operations would take place and was divided into two chief areas-the combat zone, or the area of active fighting, and the Communications Zone, or area required for administration of the theater. As the armies advanced, both these zones and the areas into which they were divided would shift forward to new geographic areas of control.[1]