text: Environmental and Terrain Considerations for Fire Support
  CLOSE AIR SUPPORT
  D-71. Because the terrain forces the enemy to concentrate his forces along roads, valleys, reverse slopes, and
  deep defilades, CAS is very effective. However, the terrain also restricts the attack direction of the CAS
  strikes. The enemy also conducts IPOE to determine the likely direction of the CAS strikes and will weight
  his air defenses along those routes. The FSCOORD must aggressively identify the enemy air defense systems
  and target them to enhance the survivability of the CAS assets.
  COMMUNICATIONS
  D-72. Communications considerations in mountain operations include:
  * Place antennas on sides of hills or mountains.
  * Make maximum use of directional antennas.
  * Plan to use retransmission capabilities.
  SECTION IV – JUNGLE OPERATIONS
  D-73. Jungle operations are usually carried out by infantry forces. FS may be limited to indirect fires and air
  support. Because small-unit operations are commonplace, greater challenges accrue to the FS personnel at
  company and BN levels.
  MUNITIONS
  D-74. In jungle terrain, most contact with the enemy is at extremely close range. If the friendly force has a
  substantial advantage in FS, the enemy will most likely try to come in as close as possible and maintain that
  close contact. Thus, the friendly force commander cannot use his FS advantage without inflicting casualties
  on his own troops. Therefore, a knowledge of the type of munitions best suited for the terrain and how to
  employ them is vital. For example, in triple-canopy jungle:
  * HE-delay penetrates the treetops and splinters the trees, creating additional fragmentation
  (splintering effect).
  * Smoke has limited effectiveness.
  * White phosphorous is effective as a marking round and in initial adjustments.
  TARGET ACQUISITION AND OBSERVATION
  D-75. The triple-canopy jungle makes observation beyond 25 to 50 m very difficult. The jungle also makes
  map reading, self-location, target location, and friendly unit location very difficult.
  D-76. Experience from World War II (WWII) and Vietnam showed that FOs must be able to adjust mortar
  and FA fire by sound, because often they cannot see the rounds to adjust them. This sound adjustment is very
  difficult and requires experience. Greater accuracy can result from the recommended adjustments of two or
  more FOs. The battery FDC can help by announcing “splash” to let the FOs know when the round should
  impact. The observer then counts the seconds until they hear the rounds detonate. By multiplying the seconds
  by the speed of sound, the observer can estimate the range to impact. The speed of sound is approximately
  350 m per second. The speed of sound varies according to temperature, wind speed and direction, relative
  humidity, and air density; but 350 m per second should be used as a start point.
  D-77. The FO must determine the observer location and ensure that the battery FDC has it plotted. The FO
  then determines the direction to the target and selects a target grid 1,000 m along the direction to the target.
  Using that direction and target grid, the FO sends a call for fire to the FDC. Add 1,000 m to the FO's position
  for safety.
  D-78. When the initial adjusting round impacts, the FO uses that impact as a known point. The FO determines
  the direction to the round, measures the difference between the direction to the target and the impact of the
  initial round, computes the lateral correction, and makes a range correction, if necessary. Using the shift from
  a known point call for fire, the FO sends the data to the FDC, reporting the new direction.