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Registering Mortars in Combat

by SFC Sean Harris
Task force, company, and platoon-level fire supporters experience difficulties in conducting successful mortar registration missions at the Joint Readiness Training Center (JRTC). There is a significant difference between registering a mortar at the beginning of a livefire exercise or practicing registration missions at the forward observer training site (FOTS) and conducting a registration mission on a nonlinear battlefield. At the JRTC, forward observers (FOs) must contend with the enemy, transfer limits, clearance of fires, civilians on the battlefield (COBs), and many other friction points. FM 6-30, Observed Fire, clearly explains the technical aspects of conducting a mortar registration, but it does not address the previously identified issues. Typically, mortars have a more difficult time achieving the five requirements for accurate predicted fires;1therefore, all FOs must know how to conduct valid mortar registrations. Consequently, this article provides the fire supporter with a logical sequence for conducting a successful registration mission.

Planning and Coordination

First, position the mortars so they can support current and future operations (next 24-36 hours). Ensure the mortars have self-located by the most accurate means available. Battalion mortars should be surveyed whenever possible. Mortars should use a PLGR (Precision Lightweight (GPS) Receiver) in the absence of survey. The PLGR should be placed on or near the base plate of the mortar. Once it displays +/- 20 meters (FOM21), it should be changed to the AVGing mode and allowed to count 300+ times.3This provides common grid, but it does not provide common direction.4To obtain common direction, the mortar platoon can coordinate with the battalion fire support officer (FSO) to conduct a simultaneous observation with the direct support field artillery battalion survey team, utilizing a celestial body.

Second, consider the possibility that the mortar will be exposed to enemy target acquisition devices while conducting the registration mission. At the JRTC, a friendly mortar's biggest threat is often an acquisition by the Q36 Weapons Locating Radar. The solution to this is simple. Fire supporters ensure the higher headquarters has their friendly mortar location and is notified when the element is firing.

Third, determine if there is sufficient ammunition to support the mission. Always consider the ability to resupply and the amount of ammunition that will be saved because of the increase in accuracy. Observers should strive for one round adjustment missions; however, this will be extremely difficult if the firing element has not met the five requirements for accurate predicted fires or has not registered.

Finally, with the commander or S3, determine or verify the best azimuth of fire (AOF) to support current and future operations. Remember the main effort is the priority. Only by plotting the mortars on a map and drawing the AOF with the 400 mils left and right fan, can one assure the selected AOF covers the task force (TF) area of operations. The FSO should not assume the mortars always have 6,400-mil capability at all firing locations.

Transfer Limits

The registration point location cannot be selected without taking into account the transfer limits of the mortar (see figure 1). FM 23-91, Mortar Gunnery, states that registration corrections can be applied 1,500 meters beyond and short of the registration point (RP) and 400 mils left and right of the weapon location.

Based on this information, the ideal RP for a 60-mm mortar would be between 1,700-2,000 meters from the mortar tube. Mortars with larger ranges, such as 81-mm or 120-mm, could require two registration points to cover their entire range. Additionally, more than one registration could be necessary when a mortar platoon is supporting a battalion with a large sector. For example, the TF FSO planning for future operations would determine the vicinity grid for the registration point. This area reflects where the S2 predicts the majority of fire missions will be requested. Then the FSO can establish the transfer point.

Considerations for a Registration Point Location
  • Future operations.
  • Maxiumum range the mortar is anticipated to fire.
  • The transfer limits of the RP.
  • The location is clear of friendly units and COBs.
  • Must be able to accurately locate it within 10 meters.
  • Semi-permanent.
  • On fairly level terrain.
  • Center of zone of fire.
  • Easily identifiable.

In most cases, the preferred RP location can be determined by subtracting 1,500 meters from the maximum range of the mortar or the maximum range the weapon is expected to fire. Figure 2 clearly illustrates this point for an 81-mm mortar. An 81-mm mortar has 12.3 square kilometers in its mortar fan (one octant). Because of transfer limitations (see Figure 1), it is impossible to cover the entire 12.3 square kilometers with one registration point. Figure 2 illustrates the benefits of registering at 4,100m (maximum range minus 1,500m) for an 81-mm mortar. A similar chart could be constructed for a 60-mm, 107-mm, and 120-mm mortar.

Once the FSO has determined where the ideal registration point would be, he plots this point on a map and considers the possibility of registering in that area. If the area is clear for a fire mission, he uses the range calculation (RNG-CALC) function on the PLGR to determine the 8-digit grid to the tentative registration point. At the TF level, the FSO selects the best FIST or COLT to conduct the mission. At the company level, the FSO selects the best observer.

Whenever possible, the FSO ensures the maneuver company or platoon is tasked with the responsibility to register the mortars. This tasking is found in paragraph 3(b) of the operations order (OPORD) tasks to maneuver units. At the task-force level, the commander or S3 tasks a company; at the company level, a platoon is tasked. This will facilitate the observer getting the security force he needs to contend with the enemy while moving to the observation point (OP) to conduct the mission. When the observer is given the 8-digit grid to the tentative registration point, he stores this grid as a waypoint in his PLGR. Finally, the company FSO/FSNCO ensures the observer has the necessary equipment to conduct the registration mission (pre-combat inspections), adequate security, and communications with the firing asset prior to departing the patrol base or assembly area. Time permitting, the observer needs to rehearse. At a minimum, the observer should review the details of the particular mission he is expected to conduct in FM 6-30. If time is available, the FO conducts a technical rehearsal with the firing element.

Execution

After a good map reconnaissance of the route, the observer uses the NAV function of the PLGR to move to the tentative registration point. Movement to the tentative registration point or OP needs to happen as quickly as possible. Often commanders get alarmed at the amount of time many registration missions take to accomplish. Everything the fire support team can do to expedite this process should be done. A +/- reading of 20 meters on the PLGR is necessary before the team moves to the RP. This will decrease the time the team is exposed to the enemy at the OP or RP.

When the observer gets within 100-500 meters of the tentative registration point, he must ensure the area is clear of any friendly units and COBs. He then decides if the area will support an OP and if a point can be found that can be accurately (within 10 meters) located, is semi-permanent, on fairly level terrain, and is easily identifiable.5A large tree is semi-permanent and can be easily identified if it is marked with some type of colored/engineer tape. The center of zone-of-fire requirement is met during the planning phase of the mission. An observer using a PLGR will be on common grid--not common survey6--with the firing element. Once the observer has found a registration point, he finds an OP that is along the gun (mortar) target line or within 500 mils of the gun target (GT) line,7outside the minimum safe distance for the weapon, and has some cover and concealment. If the observation point is within danger close of the weapon system, the observer includes DANGER CLOSE and DELAY in the method of engagement of the call for fire. Once the observer has spotted the initial round as safe, he cancels fuze delay and continues the mission.

Target Location

The registration point must be located within +/- 10 meters of its actual grid. When the tactical situation permits, the easiest way to accurately locate the registration point is to PLGR in the point using the AVGing mode.8If the FO cannot physically occupy the RP, he can accurately locate the RP with a compass, laser range finder, and PLGR. Utilizing the RNG-CALC function of the PLGR, the observer inputs the azimuth to the nearest 10 mils (magnetic/grid depending on the PLGR setup) and the observer target distance from a laser range finder. Prior to utilizing the RNG-CALC function, the observer must ensure it is accurately self-locating (+/- 20 m). As a final alternative, two observers operating from different observation points can use the resection technique to accurately locate the RP. The bottom line is that the observer must accurately locate the RP to the nearest 10 meters! Observers must understand that the accuracy of the PLGR in the RNG-CALC mode is dependent upon the accuracy of the inputted data. Therefore, the preferred technique is to PLGR in the registration point.9When this is possible, the observer marks the registration point as a waypoint after he has AVGed the grid to the registration point. He then uses the PLGR to assist in determining an observer-to-target line (OT) and OT factor10(both should be double-checked with compass and map).

Finally, the observer sends the call for fire or responds to the request from the fire direction centers (FDCs) for a registration mission11with an 8-digit grid, altitude,12and observer-to-target line. All other procedures are in accordance with FM 6-30, chapter 5. When civilians are on the battlefield or the potential for fratricide exists, the observer includes AT MY COMMAND as the method of control in the call for fire, so he can positively ensure the area around the RP is clear prior to firing each round. In restrictive terrain, the observer may need to adjust all rounds onto the RP when adjusting the sheaf. In this situation, the mortar ballistic computer determines the data to open the sheaf.

Common Mistakes To Avoid

  • Failure to ensure the last round is mathematically within 25 (50)13meters of the RP (this will require the observer to spot one round over and one round short).

  • Failure to consider the transfer limitations of the mortar when selecting the RP location.

  • Failure to locate the RP within 10 meters of its actual location.

  • Failure to maintain a DA FORM 5429-R, Section II or the equivalent drawing.

  • Failure to determine OT factor to the nearest tenth for distances of less than 1,000 meters.

  • Attempting to register during hours of limited visibility.

Summary

Conducting a valid registration mission is not difficult, but it does require a trained observer and some pre-mission planning and coordination. Special attention must be given to the selection of the best registration point location based on the transfer limits of the weapon and future operations. The observer conducting the mission cannot forget about the enemy, civilians on the battlefield, other friendly units, and, just as importantly, the technical requirements for conducting the mission. Finally, the payoff for the work that goes into planning and executing a successful registration mission is significant--every element in close contact with the enemy benefits from accurate predicted fires.

The Steps

1. Position the mortars for current and future operations.
2. Ensure the mortars have accurately self-located.
3. Select the best azimuth of fire.
4. Select the tentative RP (transfer limits).
5. Conduct equipment pre-combat inspections (PCIs).
6. Conduct radio checks with the firing element.
7. Conduct a map reconnaissance.
8. Rehearse.
9. Move to the tentative OP or RP.
10. Confirm that the RP is clear of friendlies.
11. Confirm the tentative RP location will work.
12. Accurately locate the RP (nearest 10m).
13. Conduct the registration mission.

__________

Endnotes:

1. FM 6-40, Field Artillery Manual Cannon Gunnery.

2. Figure of Merit (FOM) 1 assures the user that the PLGR is providing the most accurate data available.

3. To achieve the best results in the shortest time, allow the AN/PSN-11 to obtain a FOM of 1 before selecting AVG mode. This will prevent less accurate position solutions from being included in the averaging solution calculation. When the AN/PSN-11 is in the AVG mode, accuracy improves with time. AN/PSN-11(V)1, TM 11-5825-291-13.

4. FM 6-2, Field Artillery Survey.

5. Reference the five requirements for an RP in FM 6-30, Chapter 5.

6. Only observation teams equipped with devices (i.e., G/VLLD) that function with orienting lines can be on common survey with a firing element.

7. Outside 500 mils and the observer converges the sheaf during its adjustment.

8. This should take 5-7 minutes.

9. To be as accurate as possible, the PLGR should be reading FOM 1 (+/- 20m), placed in the AVGing mode, and allowed to count 300 times.

10. Storing both the RP and OP as waypoints and then using the PLGT to determine the exact azimuth and distance to the RP from the OP does this.

11. When MET data is not available, frequent registrations may be required based on changing weather conditions.

12. Although FM 6-30 does not require the observer to send the RP elevation, the elevation reading from the PLGR will be considerably more accurate than a map spot and should be used by the FDC whenever possible.

13. FM 6-30 states that the last round fired must be within 50 meters and refinement corrections are sent to the nearest 25 meters. FM 23-91, Mortar Gunnery, states the "the FO continues to adjust until a 50-meter bracket is split and the last fired round is within 25 meters of the target (Figure 14-1). Refinement corrections are sent to the FDC, and the mission is ended." Pg. 14-1,2. When possible, the FO should achieve the 25-meter requirement.


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