text: Chapter 13
  * While displacing, determine the direction of enemy movement, maintain contact, and report threat
  activities.
  13-60. A unit can normally screen an avenue of approach two echelons larger than itself, such as a battalion
  scout platoon screening a battalion-sized avenue of approach or a cavalry troop screening a brigade-sized
  avenue of approach. Security force units inform their higher echelon commanders of shortfalls when their
  forces lack the time or other resources to complete all screen operations. They request guidance on which
  tasks they must complete and their priority. After initiating the screen, if security force units determine their
  forces cannot complete all assigned tasks—such as maintain continuous observation of all avenues of
  approach that affect the main body’s mission—they inform their higher echelon commanders and await
  further instructions while the unit continues to screen to the best of their ability.
  Organization of Forces
  13-61. A screen normally requires the subordinate elements of the security force to deploy abreast. A screen
  force normally organizes itself into a number of observation posts determined by the number of avenues of
  approach into the main body and any additional NAIs the security force must cover, as specified by the main
  force commander. The screening force may retain a small reserve to extract endangered observation posts.
  Screen Control Measures
  13-62. The control measures necessary to conduct a screen include phase lines, observation posts, named
  areas of interest, handover lines, and contact points. Figure 13-5 depicts example screen control measures.
  Figure 13-5. Control measures used in a screen mission
  Executing a Stationary Screen
  13-63. Screening forces establish observation posts with overlapping fields of observation when
  establishing screens. Security force units adjust the locations of subordinate screening elements to take