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by CPT Steve Bullimore and SFC Lonnie Davis, Fire Spt Division Observers/Controllers

The misunderstanding of the purpose and employment of triggers continues to plague units and prevent effective execution of fires at the National Training Center's Live Fire. During defensive operations, task forces will routinely emplace triggers between 800 to 2,500 meters from their targets. This distance should correspond with the execution time of a fire mission in an "at my command" status. Each target is assigned a primary observer to fire the target as the enemy crosses the trigger. As the arbitrary distance of 800 to 2,500 meters does not correspond to the enemy's movement rate verses the time of flight plus transmission time, the enemy is not engaged as his lead element crosses the intercept point and is normally as much as a kilometer off the target.

Triggers are a physical point on the ground, a laser or lazed spot, or an action or event. Regardless of what type of trigger, they all have one thing in common: they cause us to do something. During offensive operations, the most effective triggers tend to be those based on maneuver actions or events. For defensive operations, effective triggers are a combination of physical and laser triggers. Physical triggers are easily identifiable objects and markers. A laser trigger is a direction and vertical azimuth from an observer to a spot on the ground. During defensive operations, both types have advantages and disadvantages.TYPES OF TRIGGERS

An advantage of a properly emplaced physical trigger is that multiple observers can identify it while it blends in with the existing terrain. Once emplaced, and as long as it is visible, a physical trigger allows the observer the flexibility to move. Some disadvantages are the time it takes to emplace and exposure to possible enemy fire while emplacing the trigger.

Physical triggers are either visual or thermal. A visual trigger, a VS-17 panel for example, is visible during clear daylight hours only. A thermal trigger, burning charcoal or reverse polarity tape, is visible day or night, but only as long as it produces a thermal signature. Whether you employ visual or thermal triggers, remember to always reduce the signature of that trigger on the enemy side of the trigger.

All types of triggers have limitations, and understanding those limitations help in the selection of the proper trigger for the mission. An example of physical trigger limitations is reverse polarity tape is difficult to observe beyond 5 kilometers. A 5-gallon antifreeze can containing sand and diesel will rarely emit a thermal signature beyond 6 hours. Plywood panels are difficult to conceal from enemy observation. Laser triggers minimize the limitations of physical triggers. By lazing any point on the ground and marking the direction and vertical azimuth to that point, we quickly and accurately establish a trigger. Advantages of laser triggers are that they are virtually undetectable to the enemy, they require a minimum amount of time to set in, and they do not require exposure to the enemy. Laser triggers require an observer in a FIST-V, the trigger is no longer valid if the FIST-V moves, and the trigger is only valid for the FIST who established it. When we use visual and laser triggers in conjunction with each other, we minimize the weaknesses of both. There are many other trigger types in use. It is important to understand their purposes.


When to emplace your trigger is dependent on its use and type. A thermal trigger is only effective while it emits a signature. Thermal triggers provide the best visible signature, but they have the shortest life span. Because of this time limitation, thermal triggers are best emplaced closer to the expected time of the enemy's attack. This also increases your risk in exposure to enemy fire. Burn times and small size limit the effectiveness of triggers using infrared chemical lights. While not effected by weather like fuel-burning triggers, they have a time limit and should also be emplaced as close to the enemies expected attack.

Time or weather does not affect reverse polarity tape. This allows you to emplace it as early as possible. Because it is visible through your thermal sight, it functions equally well both night and day. Other forms of visual triggers, while not visible at night, are also not limited by time. These include VS-17 panels, any form or shape of plywood marker, and existing terrain features. Establish these as early as possible to provide flexibility to the observation plan by allowing your FISTs the freedom of movement and orientation to planned targets.

Centralized or decentralized emplacement of triggers is dependent on time available. If time is available, the centralized approach, under direct supervision of the battalion FSNCO, will quickly orient all observers while using the same trigger for all observers. Centralized control allows the FSO or FSNCO to confirm the observation plan, existing obstacles and accurate trigger and target locations.

If time is not available, the decentralized approach must be used. As a minimum, the primary and alternate observers should work together to emplace the triggers. The primary observer watching while the alternate observer stakes in the trigger.

While emplacing triggers, takes some form of a global positioning system along to verify the actual trigger location in relation to the target. As soon as you establish a target, emplace the visual triggers that are not time dependent. Later, refine and add thermal triggers as necessary to augment the previously emplaced triggers. Every observer should emplace a hasty trigger, using the GVLLD for each target as the target is established.

Regardless of who emplaces the triggers, if they are not emplaced to provide maximum visibility to the observers and reduced visibility to the enemy, they are useless. If the enemy can detect your triggers, he can avoid entering into your target areas.


Both FM 6-20-40 and FM 6-30 spend little time on triggers and their employment. Both FMs give examples, and in those examples, they include fire mission processing time. A common problem in determining the trigger point is the inclusion of this processing time in the calculations. FM 6-20-40 allows 60 seconds of processing time in their example, but because it is outside the scope of the FM, it does not address what tasks are included in that time. Most units naturally incorporate their own processing time, when that time is accurately known.
The average shift time for most FA battalions is 7 minutes (from end of mission to ready "at my command" on the next mission is 7 minutes.) The 7-minute period includes target processing and the time from end of mission to the ready to fire time for the next mission.
This computation gives us a realistic idea of where or when we must shift to initiate fires on a target. To attempt to trigger fires, 7 minutes or more prior to the target reaching the intercept point is inviting failure. Too many variables are at play throughout the fire support system to accurately trigger fires on the enemy. To understand this problem, let's look at the targeted enemy force. For example, let's use a reinforced motorized rifle battalion (MRB) in the attack formation of two motorized rifle companies (MRC) up and one back. The dimensions of this formation are approximately 1,000 to 1,500 meters wide and 1,000 meters deep. If this formation is traveling at 20 KM per hour, we determine that the MRB pass time over a specific point on the ground is 3 minutes from the lead to the rear vehicle.

Enemy move rate is 20 KMPH
20 KMPH = 3 minutes per KM
1 KM - 3 minutes = 333.3 meters per minute
7 minutes X 333.3 = 2333.1 meters

At a sustained rate of fire, in 3 minutes we can trigger and fire a four-round volley effectively on the MRB. To do this effectively, we must trigger these fires at the correct time. For the battalion to fire 7 minutes out, 2,300 meters incorporates too many variables that do not allow for the accurate engagement of the target. Firing 2 minutes early will result in 50 percent of our fires impacting ahead of the enemy formation at the intended intercept point. We understand that if our timing is going to be off, it's better to be early than late. That is, however, no excuse for planning to be early. We cannot ignore the required shift time for the FA or the mortar platoon. To plan targets closer together than our shift time is inviting failure.

The problem most fire supporters face is we usually have several targets each based on an enemy course of action. A trigger is needed to determine both where and when to shift. One solution to the problem of when to shift is the employment of a separate trigger or trigger line. This trigger or trigger line is a point or line that the enemy must cross, causing a shift of assets to the target, but within the limits of shift capabilities. Using the previous example, if our shift time is 7 minutes, we cannot place our trigger line closer than 2,300 meters to the target. The purpose of the trigger line is to shift the fire support assets in time to fire "at my command" on the next target (i.e., when the enemy hits the execution trigger, we will fail to shift in time if we place this trigger closer than our shift time will allow).

The execution trigger is nothing more than the longest time of flight (TOF) plus transmission time. For example, a 35-second TOF plus a 15-second transmission time equals a total of 50 seconds. Earlier we determined that the enemy travels at 20 KMPH, which equates to about 300 meters in 50 seconds. The execution trigger is established 300 meters from the target. When the enemy crosses the trigger line, the primary observer initiates the call for fire at his command. When the enemy hits the execution trigger, the observer cancels AMC and fires the target. Accurate and massed fires on the enemy is the end result.

trigger line

In this example, the trigger line is located on the ground where the MRB must begin its turn north or south of the hill mass and outside our average shift time. Two execution triggers are emplaced to support the two planned targets. The trigger line commits the asset, and the trigger executes it.

As mentioned earlier, our own actions and events generally provide the best triggers when conducting offensive operations. When looking for, or determining the suitability of an, offensive trigger, look for a significant event or action to key the observer. Remember that timing is difficult to coordinate because all battlefield operating systems must be synchronized by time, and time is not flexible. Timing does not ensure our integration with maneuver. Triggering significant fire support events off significant maneuver events goes a long way in integrating fires with the scheme of maneuver. Very often we fire the next target simply because we finish the previous one. When we employ this method of triggering, we quickly find we are not suppressing the enemy to support the maneuver force, but that we are suppressing because we completed the previous task.

Often in offensive operations, firing early is as harmful as firing late. For example, triggering smoke fires too early while conducting a deliberate breach may result in inadequate obscuration at a critical time, as we expend all our smoke too early. Additionally, firing suppressive fires early usually results in inadequate or no suppression when the maneuver force is most vulnerable, such as just before occupation of the assault by fire position. The challenge is to ensure our trigger is accurate and well thought out.

This is an example of an offensive mission with a deliberate breach. We plan to fire smoke to obscure the breach site from enemy observation and to protect the breach force from accurate direct fires. To accomplish this mission, the smoke has to be effective before the breach force reaches the enemy's direct fire range. Additionally we must allow for initiation, adjustment, and smoke buildup. When we combine these considerations, we add both time and distance to our trigger for smoke. Now the FSO is looking for a trigger possibly 20 minutes prior to when the Task Force Commander needs effective smoke. Possible options for the triggers are when the breach force crosses a check point or phase line, or when the support force sets in the assault by fire position. The maneuver commander must understand the criticality of these calculations and understand that when the smoke is effective, it's time to move! Whatever event we use to trigger, it must allow adequate time for accurate fires in support of the maneuver force. Again, when we use specific actions or events to trigger our fires in offensive operations, we take the final step to integrate our fires with the scheme of maneuver.


Hitting a moving target is never easy to do, but it is often required to meet the commander's intent and achieve the desired results on the enemy.

We must understand triggers to be effective. There is no best solution in choosing a trigger type for a given situation. If we understand the advantages and disadvantages of each type of trigger and use those triggers in combinations, we will maximize their advantages. Emplace triggers early and continually refine them. Never become fixed to a single trigger type and always limit the execution trigger time to its minimum. By cutting execution triggers to the least amount of time possible, we limit the impact of variables, streamline our execution, and provide timely and accurate fires on target.

Development of the Brigade Scheme of Fire Support
Clearance of Fires

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