FM-3-09 Fire Support and Field Artillery Operations Download
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Denied, Degraded and Disrupted Operations 30 April 2020 FM 3-09 C-9 C-48. Propellant temperature affects the range a round will travel. Propellant has a standard temperature based on 70 degrees Fahrenheit. If the propellant is colder than standard the round will have a decreased range, if the propellant is warmer than standard the round will have an increased range to the target. A propellant is a low-order explosive that burns rather than detonates (TC 3-09.81). In artillery weapons using separate-loading ammunition, the propellant burns within a chamber formed by the obturator spindle assembly, powder chamber, rotating band, and base of the projectile. For cannons using semi-fixed ammunition, the chamber is formed by the shell casing and the base of the projectile. When the propellant is ignited by the primer, the burning propellant generates gases. When these gases develop enough pressure to overcome initial bore resistance, the projectile begins its forward motion. Table E in the tabular firing tables lists the magnitude of change in muzzle velocity resulting from a propellant temperature that is greater or less than standard. Appropriate corrections can be extracted from that table. Propellant temperature should be determined from ready ammunition on a periodic basis, particularly if there has been a change in the air temperature. For more information on the procedures see TC 3-09.81. ACCURATE METEOROLOGICAL INFORMATION C-49. With today's emphasis on FFE and trends toward longer distances, accurate MET corrections for artillery fires are crucial. Atmospheric conditions that include wind direction, wind speed, air temperature and air density along the trajectory of a projectile or rocket directly affect its accuracy and may cause the projectile or rocket to miss the desired point of impact. C-50. The Computer Meteorological Data-Profiler (CMD-P) (AN/GMK-2) is a weather measurement system developed to provide MET data to support artillery and TA units. CMD-P interfaces with the AFATDS via local area network connection and is operated by the AFATDS operator. The BN AFATDS transmits MET data to the subordinate FA units. Every effort must be made to obtain the most accurate MET corrections available. C-51. Meeting the MET requirement in D3SOE conditions can be resolved by a number of techniques if CMD-P is unavailable: • MET can be received from other units not affected by the D3SOE. • MET message via voice. • Conduct a registration if conditions are permissive. VERIFYING MET MESSAGES C-52. When the FDC receives a MET message, it should be checked to ensure that it is valid. Any peculiarities in the message should be noted. If the timeliness or validity of a MET message is doubted, that should be questioned and referred to the BN FDC. While most messages are transmitted digitally, verbal transmission of MET messages may cause copying errors, particularly if the message is copied down on something other than the standard (computer) DA Form 4200 (Met Data Correction Sheet). FDC personnel should use the procedures outlined in TC 3-09.81 to verify MET messages. C-53. Check the computer MET message heading as follows: Check message type, octant, and location entries for correctness, ensuring validity for the AO. The location of the MET message should be the midpoint between the gun and target areas. Check date-time entries to ensure they are current (date-time entries are expressed in Greenwich Mean Time). Check for possible line to line errors in the computer MET message as follows: Question drastic wind direction changes (1,000 mils or greater) or sudden reverses of wind direction from line to line, particularly if wind speeds are more than 10 knots. Direction changes greater than 1,000 mils are common when wind speeds are 10 knots or less. Question severe increases or decreases (10 knots or greater) in wind speed from line to line. Temperature accuracy is hard to evaluate because of natural erratic changes. Question a severe increase or decrease (over 20°K) in temperature from line to line.