text: Fundamentals of Operations
  enemy and a fluid forward line of troops. Sectors are best for front line units conducting a defense, making
  it easier for a higher headquarters to conduct deep operations and for subordinate units to have mutually
  supporting fires.
  Mutual Support
  3-133. Commanders and staffs consider mutual support when considering how large an area to assign
  subordinates. Mutual Support is that support which units render each other against an enemy, because of their
  assigned tasks, their position relative to each other and to the enemy, and their inherent capabilities (JP 3-31).
  In Army doctrine, mutual support is a planning consideration related to force disposition, not a command
  relationship. Mutual support has two aspects: supporting range and supporting distance.
  3-134. When two units are mutually supporting, their assigned areas are generally contiguous with each
  other. Units with non-contiguous areas are generally not mutually supporting. Supporting range is the
  distance one unit may be geographically separated from a second unit yet remain within the maximum range
  of the second unit’s weapons systems (ADP 3-0). Supporting range depends on available weapons systems,
  and it is normally the maximum range of the supporting unit’s indirect fire weapons, although certain
  capabilities employed via space and cyberspace can be used at much longer ranges. Terrain, visibility, and
  weather may limit the supporting range. If one unit cannot effectively or safely fire in support of another, the
  first may not be in supporting range even though its weapons have the required range. At higher echelons,
  communications are also a consideration. If two units cannot effectively coordinate the use of indirect fire,
  then they may not be considered in supporting range of each other. Figure 3-3 on page 3-26 illustrates a
  notional corps assigned area with noncontiguous AOs.
  3-135. Supporting distance is the distance between two units that can be traveled in time for one to come
  to the aid of the other and prevent its defeat by an enemy or ensure it regains control of a civil situation
  (ADP 3-0). These factors affect supporting distance:
  (cid:122) Terrain and mobility.
  (cid:122) Distance.
  (cid:122) Enemy capabilities, including those employed from the space, cyberspace, air, and maritime
  domains.
  (cid:122) Friendly capabilities, including those employed from the space, cyberspace, air, and maritime
  domains. (See Chapter 6 for a greater discussion of mutual support.)
  Note. Contiguous boundaries do not imply units are capable of mutual support or that their
  subordinate units have contiguous assigned areas. Therefore, mutual support between adjacent
  units and subordinate units must be part of commander dialogue to ensure the formation is
  assuming risk deliberately and at the right echelon.