text: Chapter 13
  Figure 13-8. Example of successive bound by unit and continuous marching methods of
  displacement
  Screening Operations During Limited Visibility
  13-71. Limited visibility often affects the screening force’s ground and air observation. During limited
  visibility, the screening force uses all available night and thermal observation devices and electronic
  surveillance devices. Although the screening force can use technical information collection assets to offset
  limited visibility, it should also adjust its techniques and procedures to the conditions. For example, screening
  force units may adjust the number and location of observation posts in limited-visibility conditions. They can
  establish more observation posts to cover avenues of approach that these conditions mask. They plan for
  illumination and use it when necessary. Screening force units closely coordinate their combat and
  reconnaissance patrols to prevent misidentification and friendly fire incidents. Noise and light discipline
  prevents compromise of observation posts by enemy reconnaissance forces. Additional observation posts
  along enemy avenues of approach can provide depth to facilitate the detection of enemy forces that eluded
  forward security elements.
  GUARD
  13-72. Guard is a type of security operation conducted to protect the main body by fighting to gain time
  while preventing enemy ground observation of and direct fire against the main body (ADP 3-90). A guard
  differs from a screen in that a guard force contains sufficient combat power to defeat, cause the withdrawal
  of, or fix the lead elements of an enemy ground force before it can engage the main body with direct fire. A
  guard force routinely engages enemy forces with direct and indirect fires. A screening force, however,
  primarily uses indirect fires or close air support to destroy enemy reconnaissance elements and slow the
  movement of other enemy forces. A guard force uses all means at its disposal to prevent enemy forces from
  penetrating to a position to observe and engage the main body. It operates within the range of the main body’s