text: Chapter 17
  17-39. Once the enemy commits in the engagement area, the fire plan causes the enemy to fight in as many
  directions as possible. This serves to further slow its advance, disrupt its command and control, and reduce
  its ability to mass, allowing friendly forces to provide interlocking fires with flank shots on individual targets.
  Combining fires from multiple directions with the random orientation of individual obstacles further confuses
  the attacker. For direct fires, units consider the use of TRPs and supplementary positions to reorient fires.
  They also consider the use of protective obstacles to protect the force. The fire support officer and fire support
  teams plan targets to hold the enemy in the engagement area and aim final protective fires on critical mobility
  corridors that may let the enemy threaten friendly positions.
  Turn Effect
  17-40. Turn is an obstacle effect that integrates fire planning and obstacle effort to divert an enemy
  formation from one avenue of approach to an adjacent avenue of approach or into an engagement area. To
  accomplish the turn effect, the obstacles and fires must—
  * Prevent the enemy from bypassing or breaching the obstacle.
  * Cause the enemy to bypass in the desired direction.
  * Maintain pressure on the enemy throughout the turn and exploit its exposed flank.
  17-41. Developing a turn obstacle requires mobility corridors and avenues of approach that are well defined
  by restricted terrain. To achieve a turn effect, the obstacles must have a subtle orientation relative to the
  approach of the attacking force. The obstacles and fires allow bypasses in the direction that is desired by the
  friendly scheme of movement and maneuver (or scheme of maneuver). Obstacles at the start of the turn are
  visible to the attacking force and look more complex than those in the direction of the turn.
  17-42. The anchor point, the initial point of the turn, is where most turn obstacles fail. Therefore, it is critical
  that units reinforce the anchor point with concentrated direct and indirect fires to achieve the turn effect.
  Units normally anchor turn obstacle groups to restricted terrain or to a strong point. They approve fire support
  coordination measures, which enable the focus of all available fires first at the anchor point. When the enemy
  encounters the obstacle, the combination of fires, obstacles, and terrain must limit their ability to breach or
  bypass at the anchor point.
  17-43. Units plan an indirect fire target or group to turn the enemy away from the anchor point. They focus
  enough direct fire assets to deal with the size of the enemy force expected at that point; for example, if an
  enemy company is expected at the anchor point, then at least one friendly platoon should be allocated to mass
  fires at that point. If the enemy breaches the obstacle at the anchor point, the turning effect could be lost—
  compromising the friendly defensive plan.
  17-44. The critical task in achieving the turn effect is to use obstacles and overwhelming fires to cause the
  enemy to move in the direction that is desired by the friendly unit. As the engagement progresses, the friendly
  force prevents enemy attempts to breach the obstacle by designating enemy breaching assets as priority
  targets. Direct fire weapon systems are the primary means for destroying enemy breaching equipment.
  Artillery- and aviation-delivered fires can attack individual targets, but they may be less timely. Plan indirect
  fires—artillery and mortars—in front of, on top of, to the side of, and behind obstacles to maximize their
  effect as combat multipliers. Developing fire control measures through the planning of NAIs, TAIs, triggers,
  and targets to support obstacles in the obstacle group will make indirect fires more responsive and effective.
  17-45. Units develop a fire plan with fire control measures that allow them to shift fires as necessary to
  cover the turn effect. Direct and indirect fires shift in unison to attack and maintain pressure on the enemy
  force’s flank. Fires covering the length of the turn effect are less focused than at the turn point. Company
  commanders facilitate this by assigning platoon sectors of fire between TRPs. Units usually execute indirect
  fires in groups instead of aiming at individual targets. Direct and indirect fires continue throughout the length
  and depth of the turn effect. These fires simultaneously exploit the vulnerability created by the turn effect
  and protect the integrity of the obstacles.
  RELATIVE LOCATION
  17-46. Relative location refers to the location of a tactical or protective obstacle in relation to maneuver or
  fire control measures such as avenues of approach, BPs, or engagement areas. Engineers and other
  countermobility planners describe planned obstacle locations in relation to maneuver or fire control measures