text: Chapter 7
  expressed asOAKOC. (See ATP 2-01.3 and ATP 3-34.80 for information on analyzing the military aspects
  of terrain.)
  Engagement Area Development
  7-132. The BCT commander and staff develop EAs,to include engagement criteria and priority,to cover
  each enemy avenue of approach. Within the BCT’sMBA,the commander determines the size and shape of
  the EAs by the relatively unobstructed line of sight from the weapon systems firing positions and the
  maximum range of those weapon systems.Once the commander and staff select EAs,the commander arrays
  available forces and weapon systems in positions to concentrate overwhelming effects into these areas. The
  commander routinely subdivides EAs into smaller EAs for subordinates using one or moreTRPsor by key
  terrain or prominent terrain feature. The commander assigns sector of fires to subordinates to ensure complete
  coverage of EAs and to prevent fratricide and friendly fire incidents. Never split the responsibility for an
  avenue of approach or key terrain.
  7-133. Security area forces, to include field artillery fire support teams and observers, employ fires to
  support operations forward of the BCT’s MBA using precision and other munitions to destroy enemy
  reconnaissance and security forces and identified HPTs, and to attrit enemy forces as they approach the
  BCT’s MBA. The employment of fires within the security area also helps to deceive the enemy about the
  location of the BCT’s MBA. The BCT fire support officer plans the delivery of fires at appropriate times and
  places throughout the area of operations to slow and canalize the enemy force as the enemy approaches. The
  employment of fires allows security area forces to engage the enemy without becoming decisively engaged.
  To prevent fratricide,alliedcasualties,civilian noncombatant casualties,and excessive unintended collateral
  damage,the commander designates fire support coordination measures (such as no-fire areas,restrictive fire
  areas, restrictive fire lines, fire support coordination lines, and restricted target lines) where security area
  forces are positioned. The commander establishes these measures in order to exercise restraint and balance
  the need for combat action and that of maintaining the legitimacy of the mission and to prevent unintended
  negative effects. The commander uses fires to support the withdrawal of security forces once shaping
  operations are completed within the security area and the defending unit is prepared to conduct MBA
  operations.
  7-134. Engagement criteria are protocols that specify those circumstances for initiating engagement with
  an enemy force. Engagement criteria may be restrictive or permissive in nature. For example, the BCT
  commander may instruct a subordinate battalion commander not to engage an approaching enemy unit until
  the enemy commits to an avenue of approach. The commander establishes engagement criteria in the direct
  fire plan in conjunction with engagement priorities and other direct fire control measures to mass fires and
  control fire distribution.
  7-135. Engagement priority specifies the order in which the unit engages enemy systems or functions
  (FM3-90-1). The commander assigns engagement priorities based on the type or level of threat at different
  ranges to match organic weapon systems capabilities against enemy vulnerabilities. Engagement priorities
  are situationally dependent and used to distribute fires rapidly and effectively. Subordinate elements can have
  different engagement priorities but will normally engage the most dangerous targets first,followed by targets
  in-depth or specialized systems,such as engineer vehicles.
  7-136. A target reference point is a predetermined point of reference, normally a permanent structure or
  terrain feature that can be used when describing a target location(JP 3-09.3). The BCT and subordinate units
  may designate TRPsto define unit or individual sectors of fire and observation,usually within the EA.TRPs,
  along with trigger lines,designate the center of an area where the commander plans to distribute or converge
  the fires of all weapons rapidly to further delineate sectors of fire within an EA. Once designated, target
  reference points may also constitute indirect-fire targets.
  7-137. Atrigger lineis a phase line located on identifiable terrain that crosses the engagement area—used
  to initiate and mass fires into an engagement area at a predetermined range for all or like weapon systems
  (ATP3-21.20). The BCT commander can designate one trigger line for all weapon systems or separate trigger
  lines for each weapon or type of weapon system. The commander specifies the engagement criteria for a
  specific situation. The criteria may be either time-or event-driven,such as a certain number or certain types
  of vehicles to cross the trigger line before initiating engagement. The commander can use a time-based fires
  delivery methodology or a geography-basedfires delivery.