FM-3-09 Fire Support and Field Artillery Operations Download
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Appendix D D-12 FM 3-09 30 April 2020 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 meters per second. The speed of sound varies according to temperature, wind speed and direction, relative humidity, and air density; but 350 meters per second should be used as a start point. D-70. 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 meters 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 meters to the FO's position for safety. D-71. 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. D-72. If the FO's position location is poor, the initial round location will be poor too. The FO can use the initial round to re-determine his location. For example, the FO's call for fire told the FDC to fire grid 123456, direction 0200. The round impact is nowhere near the target. The FO then determines the direction and range to the burst. The FO plots a back-azimuth from the burst and estimates range along that direction to replot the FO's position. Then, using the new position location, FO reinitiates the mission. D-73. Vietnam and WWII also showed that the first round in adjustment should be white phosphorous. Because both the FO's location and the location of other friendly elements may have been doubtful, white phosphorous was usually fired first to avoid inflicting casualties on friendly personnel. (Using a 200-meter height of burst can help the FO see the first round.) D-74. Creeping fires were also used extensively in Vietnam and WWII. The FO adds 300 to 400 meters to the target location in case the FO's position location is wrong. Then the FO makes corrections of no more than 50 meters until the fires are on target. In Vietnam, this process sometimes started with an air observer and was taken over by the ground observer once the ground observer was able to see the rounds. The air observer was often required to relay fire requests from the ground because the terrain severely limited the ranges of radio communications. The creeping method of adjustment is used exclusively during danger close missions. Danger close in close air support, artillery, mortar, and naval gunfire support fires, the term included in the method of engagement segment of a call for fire which indicates that friendly forces are within close proximity of the target (JP 3-09.3). The observer makes range changes by using corrections of 100 meters or less and creeping the rounds to the target. The observer must know where all friendly troops are to avoid endangering them. All weapons that will FFE are used in adjustment. For battalion missions, batteries should be adjusted individually. D-75. Marking rounds can be fired to help the FO determine his own location. The use of marking rounds also helps ensure that the FDC knows in what area the friendly unit is, which ensures more responsive fires. A marking round is usually white phosphorous fired 300 to 400 meters forward of friendly units at 200 meters height of burst. The FDC plots a target, fires a white phosphorous round, and sends the grid of the white phosphorous impact to the FO. The FO then has a known position on which to orient. D-76. Because of the close combat, laser range finders may not be of great use; however, night vision devices are extremely critical. D-77. Air observers. Air observers can be important in jungle warfare. They can detect enemy movements that ground forces have no way of seeing. They can act in concert with ground observers to deliver accurate fires on enemy elements in close contact with friendly forces. Also, the air observers can relay calls for fire from ground elements to the FDC. D-78. Air observers can help direct close air support assets against enemy targets. Because ground observers cannot see the whole battlefield, the air observer marks targets for the close air support sortie (by use of flares, white phosphorous, or smoke). Caution must be taken, and positive identification of the target must be made.