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The enemy attack came hard against the two infantry battalions set in a hasty defense along the ridgeline. Indirect fires rained steel, smoke, and white phosphorus on the attackers, killing the infantry, blinding their gunners, and burning their light vehicles. Though effective, the fires in closer were not as dense as they should have been. In particular, the battalion and company mortars were not achieving the accuracy necessary to build that final wall of steel in front of the U.S. positions. Ideally, the fires should have broken the enemy before they could engage the U.S. infantry. That would not be the case in this fight, all because the mortars had not received the correct meteorological (MET) data.

If the above sounds unlikely, think again! Observers at the Joint Readiness Training Center (JRTC) consistently report that battalion fire support elements (FSEs) fail to deliver accurate and timely meteorological (MET) messages to battalion and company mortar sections.That failure means that maneuver commanders do not get full benefit of their organic fire support systems.

Accurate MET equals accurate fires

Mortar sections must get MET messages if they are to provide accurate fire support. Meteorological messages provide information needed to compensate for the effects of weather on the projectile in flight. The battalion FSE is responsible for accurately providing MET data to mortar sections in a timely manner. Firing data must compensate for variations in air temperature, air density, and the speed and direction of the wind (FM 6-40, Tactics, Techniques, and Procedures for Field Artillery Manual Cannon Gunnery, Chapter 11). The MET section generates several types of surface-to-surface MET messages for the fire support system. Those include computer, ballistic, and target acquisition MET messages (FM 6-121, Tactics, Techniques, and Procedures for Field Artillery Target Acquisition, Chapter 2). Indirect fire delivery assets, including artillery and mortars, use computer and ballistic MET messages.

Mortars need both MET formats

Usually a field artillery (FA) battalion disseminates the MET in a timely manner, but not in the format needed by the mortar section. Rotational units at JRTC often mistakenly believe that mortars only use a ballistic MET, not a computer MET. In fact, mortar sections use both, based on the section's needs. Mortars use the ballistic MET message when computing manual firing data off the M-16 plotting board. They use computer MET messages when computing firing data with the M23 mortar ballistic computer (MBC). Like all data processors, the MBC has been upgraded several times and that has changed its data requirements. In the early 1990's, it used the 2a processor chip and required the ballistic MET message. It was then upgraded to the 3a processor chip, which can receive a computer MET message.

Battalion FSEs must know how the mortars are computing data when disseminating meteorological data. In split section operations, the fire direction center (FDC) can use the MBC and the plotting board (FM 23-91, Mortar Gunnery, Chapter 3) in order to have a primary and a check computer. Mortar O/Cs report that mortar FDCs often depend on the MBC and ignore the M-16 plotting board as a secondary check. Battalion FSEs contribute to this trend by not sending both MET messages, when in most situations the mortar sections must have the ballistic and computer MET. Consequently, battalion FSE personnel must understand the differences and similarities between the two messages. Moreover, they should know how to properly transmit them.

The different formats make a difference

The ballistic MET message is similar to the computer MET message. "They both determine the corrections needed to compute firing data so that the section has better accuracy and target effect without registering every two to four hours."(FM 23-91, Chapter 4) Both messages come in two parts, the introduction and the body. The data contained in the body lists zone heights in meters in both formats. That is where the similarities end.

As the old saying goes, "The devil is in the details," the devil in the two MET formats is in their differences. The computer MET message measures wind direction in tens of mils, speed in knots, temperature in Kelvin, and pressure in millibars. The computer MET message is recorded on DA Form 3677 and distributed via hard copy or voice, transmitted on digital systems with a SYS; MET message (AFATDS, IFSAS, BCS), and then input through a MET: CM into the MBC (see Figure 1). The ballistic MET message gives wind data in hundreds of mils for direction and speed in knots. The ballistic MET provides temperature and pressure data as well, but gives data as percents of the standard atmosphere, preinstalled in the MBC at the factory and commonly referred to as "standard MET," not a specific measurement. These differences make it impossible to interchange the MET messages, so it is imperative that the FSE provide the correct MET needed by the mortar section (see Figure 2).

The factory installed standard MET message contained in the MBC can be used in the absence of MET data. However, the information contained in this message assumes a standard atmosphere at sea level. According to FM 6-16, Tables for Artillery Meteorology (Electronic) Ballistic Type 3 and Computer Messages, the International Civil Aviation Organization defines standard atmospheric conditions as: dry air, 0% humidity; no wind, 0 knots; surface temperature of 15 deg C with a decrease, or lapse rate, of -6.5 deg C per 1000 meters and a constant temperature of 56.5 deg C between 11,000 and 25,000 meters; surface pressure of 1,013.25 mb decreasing with height; and a surface density of 1,225 grams per cubic meter (gm/m3 ). Unfortunately, the actual atmosphere rarely reflects these standards. That means it is VITAL that meteorological data be applied regularly.

Get it right before it goes out!

Before the FSE disseminates an MET message, the FSE must ensure the message is valid. All too often components of the fire support system use different versions of digital equipment. These differences can inadvertently alter the information in an MET message. Human error can add to the problem when an MET message is transmitted over the radio. For that reason the MET message must always be read back to the sender to confirm the data. FM 6-40, Tactics, Techniques, and Procedures for Field Artillery Manual Cannon Gunnery, Chapter 11, provides guidelines for checking an MET. Knowing these guidelines makes it possible for FSE personnel to validate the MET message so the mortar ballistic computer will not reject the data or cause errors in manual computations.

Check for errors in both computer and ballistic MET message IAW FM 6-40, Chapter 11:

• The heading of an MET message includes important information needed to verify a MET's validity, such as the MET station location. Preferably, the MET is flown no more than 20 km from the midpoint of the trajectory and is less than two hours old. However, METT-T considered, the MET should normally be used when flown within 80 km of the midpoint of the trajectory and is less than 4 hours old.

• Check for drastic wind direction changes (1000 mils or greater) or sudden reverses of wind direction from line to line, particularly if wind speeds are more than 10 knots.

• Check severe increases or decreases (10 knots or greater) in wind speed from line to line.

• Check for a severe increase or decrease (over 20 degrees K) in temperature from line to line.

• Check for differences in identification line pressure and surface pressure. Both should match.

• Check for increases in pressure between lines. Pressure should decrease smoothly from line to line. Pressure will never increase with height in nature.

If any of the above mentioned criteria are identified, contact your FDC, or, if possible, your MET section, to verify the validity of the MET message.

Since a mortar round's maximum ordinate is 3,039 meters, only the first eight lines of the MET message are needed. There is no need to send the full 27 lines. However, mortar rounds travel through at least three changing layers of atmospheric conditions, affecting the ballistics of the round significantly.

Transmission Protocols Avoid Errors

Once the battalion FSE validates the MET message, the FSE must transmit it in a format the MBC operator can easily use. Often battalion FSEs try to send MET messages to the mortar fire direction center (FDC) digitally when mortar FDCs normally prefer hard copy. Sometimes sending a hard copy is not possible and the message must be voice transmitted. If that is the case, ensure that both the sender and the receiver have DA Form 3637 for ballistic MET and DA Form 3675 for computer MET. This gives them both a common frame of reference.

The FSE should understand how the MBC operator inputs the MET message. The heading of the MET message has four six-character groups. When the MBC operator prepares to enter an MET message, he presses the "MET" key, selects "NEW" then "SEQ", waits for a group of six numbers to be sent, enters them, then presses "SEQ" again and waits for six more numbers. These refer to quadrant and latitude and longitude, or MET station location. If the battalion FSE sends an error, the MBC operator probably will not realize it. Continuing through group five brings the MBC operator to the body of the MET message. This consists of up to 27 lines of MET data, each broken into two eight-number groups. The MBC operator expects to receive the data as a series of numbers; he enters eight numbers and hits "SEQ", repeating it until complete. If the data comes any other way, it confuses him. That interrupts the flow and data is lost. Having the proper forms available at both ends before transmission can avoid such difficulties.

Conclusion: Get the MET data right and get steel on the target!

Understanding MET and its use to increase mortar accuracy is a consistent problem at JRTC. Training mortar FDCs and battalion FSEs in MET and use of the MET TTPs discussed above will help improve their ability to provide timely and accurate fires. The pursuit of the five elements of accurate predicted fires is constant. Battalion FSEs must aggressively obtain MET messages from the FA battalion FDC. The FSE must validate and then disseminate them in an equally timely and accurate fashion. By doing so, the FSE will increase first-round accuracy and lethality. It will also conserve ammunition and better support its maneuver forces with accurate, predictive fires.

Figure 2. Sample Ballistic MET message