text: Chapter 17
  that location depending on the effects of terrain. Similarly, the obstacle effect symbols in table 17-1 have
  different orientation, meaning, and application than the tactical mission task symbols they resemble.
  Block Effect
  17-24. Block is an obstacle effect that integrates fire planning and obstacle efforts to stop an attacker along
  a specific avenue of approach or to prevent the attacking force from passing through an engagement area. To
  accomplish the block effect, the obstacles and fires must—
  * Prevent the enemy from bypassing or breaching the obstacles.
  * Maximize available standoff.
  * Stop enemy forward movement.
  17-25. Units consider obstacle protection when planning fire control measures. The first mission of the
  overwatching force is to stop any bypassing or breaching attempt. They respond to any attempt to breach or
  bypass with direct and indirect fires. Block obstacles stop enemy maneuver and cause the enemy to commit
  breaching assets that can be destroyed by fire.
  17-26. To support survivability, units position forces to provide standoff so that the force can survive. The
  engagement area must cover the width of the entire avenue of approach. The maximum effective range of the
  overwatching weapons minus the standoff distance limits the depth of the engagement area. The commander
  positions forces so that they can mass interlocking fires across the entire avenue of approach. The defending
  force must be able to concentrate all available fires within the obstacle group. Units array weapon systems in
  depth based on their maximum effective ranges.
  17-27. The success of a block obstacle is measured by its impact on the enemy advance, not by enemy
  losses. The block effect is the most resource-intensive obstacle effect to achieve and is usually only limited
  to critical points on the battlefield. Normally, the purposes of forces overwatching a block obstacle is to
  defeat lead enemy units and cause the attacker to reconsider the deployment of follow-on forces.
  Commanders allocate sufficient combat power to achieve all effects of the obstacle which demand protecting
  the obstacle and defeating enemy forces encountering it.
  17-28. Achieving the block effect requires the integration of complex obstacles—those that require more
  than one reduction technique to create a lane—with massed fires to defeat the breaching effort of the attacking
  force. Units array obstacles successively in a concentrated area. When the attacking force reduces one
  obstacle integrated with massed fires, it encounters another obstacle integrated with massed fires. Obstacles
  must defeat the mounted and dismounted breaching efforts of the attacking force. They must span the entire
  width of the assembly area, allowing no bypass. Obstacles intended to prevent an attacking force from using
  a specific assembly area should be readily visible to discourage further progress forward. Obstacles used to
  prevent an attacking force from passing through an engagement area should be less visible to avoid
  discouraging the enemy from entering the engagement area. Fires should be planned, not on the obstacles,
  but on the locations where enemy forces will move to when they are blocked.
  Disrupt Effect
  17-29. Disrupt is an obstacle effect that focuses fire planning and obstacle effort to cause the enemy to
  break up its formation and tempo, interrupt its timetable, commit breaching assets prematurely, and attack in
  a piecemeal effort. The disrupt effect also helps to deceive the enemy concerning the location of friendly
  defensive positions, separate combat echelons, or separate combat forces from its logistics support. To
  accomplish the disrupt effect, the obstacles and fires must—
  * Cause the enemy to deploy early.
  * Slow and disrupt part of the enemy force.
  * Allow part of the enemy force to advance unimpeded.
  17-30. Obstacles must normally attack half of the targeted avenue of approach to achieve the disrupt effect.
  The obstacles should not require extensive resources for construction or emplacement. Units normally use
  the disrupt effect beyond engagement areas, while being careful not to inadvertently discourage the enemy
  from entering the engagement area.