text: FM 7-100.1________________________________________________________________________________
  2-20. A theater headquarters provides flexible and responsive control of all
  theater forces. When there is only one theater, as is typical, the theater head-
  quarters may also be the field headquarters of the SHC, and the CGS may
  also be the theater commander. Even in this case, however, the CGS may
  choose to focus his attention on national strategic matters and to create a
  separate theater headquarters, commanded by another general officer, to
  control operations within the theater.
  2-21. When parts of the strategic campaign take place in separated geographi-
  cal areas and there is more than one major line of operations, the OPFOR
  may employ more than one theater headquarters, each of which could have
  its own theater campaign plan. In this case, albeit rare, the SHC field
  headquarters would be a separate entity exercising control over the multiple
  theater headquarters.
  2-22. Theater command provides flexibility to the OPFOR, since the exis-
  tence of one or more separate theater headquarters enables the SHC to fo-
  cus on the strategic campaign and sustaining the forces in the field. A
  theater headquarters acts to effectively centralize and integrate General
  Staff control over theater-wide offensive and/or defensive operations. The
  chief responsibility of this headquarters is to exercise command over all
  forces assigned to a theater in accordance with mission and aim assigned by
  the SHC. A theater headquarters links the operational efforts of the OPFOR
  to the strategic efforts and reports directly to the SHC.
  Administrative Force Structure
  2-23. The OPFOR has an administrative force structure that manages its
  military forces in peacetime. This structure is the aggregate of various military
  headquarters, organizations, facilities, and installations designed to man,
  train, and equip the forces. In peacetime, forces are commonly grouped into
  corps, armies, or army groups for administrative purposes. An army group
  can consist of several armies, corps, or separate divisions and brigades. The
  administrative force structure also has responsibility for disaster manage-
  ment and support to other State agencies. In some cases, forces may be
  grouped administratively under geographical commands designated as
  military regions or military districts.1 Normally, these administrative group-
  ings differ from the OPFOR’s go-to-war (fighting) force structure.
  2-24. The administrative force structure includes all components of the
  Armed Forcesnot only regular, standing forces (active component), but also
  reserve and militia forces (reserve component). For administrative purposes,
  both regular and reserve forces come under the headquarters of their respec-
  tive service component. Each of the six service components is responsible for
  manning, equipping, and training of its forces and for organizing them within
  the administrative force structure.
  2-25. If the General Staff or SHC elects to create more than one theater
  headquarters, it may allocate parts of the administrative force structure to
  each of the theaters, normally along geographic lines. One example would be
  to divide Air Force assets into theater air armies. Another would be to assign
  1 A military district may or may not coincide with a political district within the State government.