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Forward Observer

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Intent and Scope:

  • The intent of the guide is to provide the basic skills and techniques to effectively fill the role of a Forward Observer within the scope of ArmA 3 and the UO modpack.
  • The scope of this guide includes target location techniques and communication procedures that are most relevant to game-play within ArmA 3 on UO servers.
    A Forward Observer prepares to call for fire.

Mission of the Forward Observer

The mission of the forward observer is to locate targets and employ indirect (Artillery, Mortar, Rocket) fire to engage the enemy. The FO is also responsible for advising the commander on fire-planning and ensuring that the commander is aware of indirect fires being called in support of and in the vicinity of their troops. To accomplish their mission, the FO must be competent in land navigation, target recognition, target location techniques, adjustment of indirect fire techniques, communication, and situational awareness. The FO can be attached to any type of unit, but is most likely to be found attached to front-line maneuver units such as infantry or armor. Secondary duties may include battlefield intelligence, utilizing their target location skills and equipment to report on enemy movements and strength within their AO. The FO may also be called upon to employ rotary and fixed-wing aircraft in support of maneuver elements when a JTAC or FAC is unavailable.

Preliminary Knowledge

This guide assumes the reader has a competent level of land navigation ability, and radio communications ability. Some things to note that depart from the standard practices of these two skills.

Mils vs Degrees

While most land navigation is done using degrees, indirect fire demands a higher level of precision at the Observer, FDC, and Gunline levels. As such mils are the standard unit of angular measurement whenever any type of indirect fire is being employed. While there are 360 degrees in a circle, there are 6400 mils in a circle.

Mil-Relation Formula

The mil-relation formula explained.

The mil-relation formula allows for the estimation of range based on the angular measurement of the dimensions of an object, or to convert an angular difference between two points into a physical distance in meters. Further information on range-finding can be found in the range-estimation using optics guide. Estimating deviation is covered in the Observing and Adjusting Fire portion of this guide.

Radio Procedure

For indirect fire, clear communication of data can mean the difference between an effective fire mission and dead friendlies. Two practices are used to ensure this. First, numbers are always read off by their digits, unless they have either two or three zeros.

For example a direction of 1435 mils is read off as


3200 however can be read off as


or 1000 as simply


It is almost universal that any data is repeated by the receiver to be verified by the sender. Data is generally read off clearly and slightly slower to account for recording of data.

Finally, the term "Repeat" is never used when asking to resend a transmission, as the word in the context of a call for fire indicated the FO would like the same mission re-fired by the firing unit. "Re-send" or "Say again" should be used.

Equipment Setup

The ACE mod for ArmA 3 has a number of useful aids for Forward Observers.

Vector 21

The Vector 21 is a powerful rangefinder/binocular that is especially useful for observing indirect fire. Documentation on controls can be found here. Before usage, the observer should ensure the vector is set to use mils instead of degrees.

DAGR and MicroDAGR

The DAGR and MicroDAGR are GPS navigation aids that allow the user to easily self-locate, and combined with the Vector, can accurately give grid and elevation for targets. The DAGR simply allows for a readout of the user's current location, or the location of the target lased by the Vector. The MicroDAGR is a more advanced model with features such as a map display and storage of multiple way-points. As with the Vector, the user should ensure their GPS is set to use mils instead of degrees.

Target Location

Target location is the process by which a target on the actual battlefield is located and that location is communicated to a indirect fire unit in a manner that they can interpret and create a firing solution from. A high level of skill in target location is key to a FO's ability to direct timely and accurate fire support of maneuver elements. Three primary methods are used for target location, Grid, Polar Plot, and Adjust from Known Point.


The standard method of target location is grid. Grid is simply the most accurate grid-reference of the target that the FO can obtain. Typically this is at minimum a 6-digit grid, locating a target within 100m of its actual position. For more accurate missions (such as destruction of a specific target) or more accurate munitions (GPS-guided) an 8- or 10-digit grid should be obtained. Depending on the capabilities and procedures of the fire-direction center (FDC) at the indirect fire unit, determining a target's altitude (elevation) may fall on either the FO or the FDC to determine.


  • Does not require FDC to know the observer's position.
  • Only requires a map (and possibly map tools) to obtain a grid and altitude.
  • With specialized equipment (Vector 21 and DAGR) is the fastest and most accurate method.
  • Can be coupled with guided munitions for extremely accurate fires.


  • Can be difficult to determine if target is not within the vicinity of easily identifiable terrain features.
  • Can become more difficult as range increases.


A Polar Plot

Polar plot is the method of location that utilizes the location of the observer and the target's direction and distance from that observer. First and foremost it requires the FDC knows the accurate location of the observer when the location is transmitted. Second it relies heavily on the observer's ability to estimate range. In a polar mission, the target's DIRECTION from the observer in mils is given, followed by its DISTANCE in meters.


  • Only a compass and FO's location is required.
  • Given limited equipment is generally the fastest method to get rounds within the vicinity of the target.
  • Can be used effectively for targets difficult to locate via terrain or landmark association (forests, deserts, plains)


  • Relies heavily on FO's ability to estimate range.
  • Is not likely to result in first-round impact on targets.
  • FO must constantly update FDC on their location when re-positioning, making it difficult to use in support of rapidly moving units.

Shift from Known Point

Shift from known point is typically the least-common approach to target location, but can be useful in certain circumstances. Shift missions determine target location in relation to a point known by BOTH the FO and the FDC. First, a direction in mils is obtained from the Observer to the Target (similar to a polar mission) known as the OT direction. Next a lateral (left/right) shift from the Known Point to the Target is estimated in meters. Then a range change (add/drop) between the Known Point and the Target is obtained in meters. Finally, if significant, a vertical shift (up/down) in altitude is determined from the Known Point to the Target in meters. To summarize a Shift mission requires a Known Point and the target's difference in Lateral Distance, Range, and Altitude in relation to that known point.

A Shift from Known Point


  • Can be done without the aid of a map or binoculars if the observer can visually identify the known point and the target, and obtain a reasonably accurate bearing to the target.
  • If required, an FO can obtain the information from units on the ground and relay to the FDC if the FO cannot directly observe the target.
  • Observer position is not required to be known by the FDC. Can be used to adjust fire when the FO is on the move or must re-position.
  • Can quickly adjust off previous fire mission targets provided their data is retained by the FDC, allowing for faster re-engagement if new targets appear nearby.


  • Requires good range and deviation estimation by the FO.
  • Requires an easily identifiable and specific point both visually and on the map.
  • Not likely to achieve first-round impacts.

Target Description

Target description from the FO to the FDC is crucial for the firing unit to determine the type of round, fuze, and volume of fire they will utilize to engage the target described. While FO's can request a specific round/fuze combination or number of rounds to be fired, typically this is best left up to the FDC, as they have a better idea of the capabilities and the limitation such as available ammunition. Similar to a contact report, with a few changes, a good target description includes the following.

"THREE (number) BTRs (what) in the OPEN (protection), HALTED (doing) on the road in 200M COLUMN (size and shape) ATTITUDE 3900 (orientation)"


  • Infantry, fortifications, vehicles, tank, buildings, etc. What is the target composed of?


  • Diggings in, occupying buildings, on the move, hiding. What are they doing?


  • Squad, Platoon, Company, specific numbers. How many are there?


  • Trenches, Bunkers, Buildings, Ditches, Exposed. What is their degree of protection?


  • Length, Width, Orientation. Linear, Rectangular, Circular. What is the size and shape of the area they are occupying?

Call for Fire

Using target location and target description, the FO is ready to request for indirect fires from a firing unit using a transmission known as a "Call for Fire". The call for fire is composed of three elements. The first transmission is the Observer ID and Warning Order. The second is the Target Location. The third and final transmission is the Target Description.

Observer ID and Warning Order

The first transmission lets the firing unit's FDC know who is requesting fire (callsign) and what the type of mission (warning order) it will be. As common in radio procedure, the transmission beings with a "You, this is Me" statement. The observer will follow up with type of mission (Adjust, Fire for Effect, Immediate Suppression, Immediate Smoke, Illumination, etc.) finally they will indicate the method of target location being used. They will end the transmission with "Over". The FDC will then repeat exactly what they heard, followed by "Out." before the FO continues on to the second transmission to ensure all data was heard and recorded correctly. Note: for a Shift mission, the name of the known point is included in the warning order.

Warning Orders

Adjust Fire

  • Used when the FO is not certain the target location is extremely accurate (within 50 meters) The firing unit will fire one round (typically an HE round with Impact fuze) for each adjustment made until on target and fire-for-effect is requested.


  • Used when the FO is absolutely certain of the target's location, and wishes for the entire firing unit to engage without adjusting rounds first.

Immediate Suppression

  • Used for when an FO needs immediate fires, usually for troops in contact.or a target of opportunity Standardized by the firing unit (typically 2 Rounds HE), the FDC can expedite the mission as soon as target location is received.

Immediate Smoke

  • Similar to immediate suppression but uses smoke or white phosphorus for screening rather than suppressing the enemy.


  • Typically for inactive target, designed to fire rounds at intervals in order to suppress a target for a period of time, not necessarily to destroy or neutralize them. Duration and interval can be specified by the FO in the target description.

FO Sends

"FDC this is FO, Adjust Fire Polar, Over"

FDC Responds

"FO, this is FDC, Adjust Fire Polar, Out."

Shift Mission

"FDC, this is FO, Adjust Fire Shift from KP1, Over"
"FO, this is FDC, Adjust Fire Shift from KP1, Out."

Target Location

Next, the FO will provide the target location using one of the three methods listed above (Grid, Polar, Shift from KP), and the relevant data that corresponds with each method. Once again the FDC will repeat what they heard and recorded to verify.


"123 456. Altitude 440, Over."
"123 456, Altitude 440, Out."


"Direction 4600, Distance 2100, Over"
"Direction 4600, Distance 2100, Out"


"Direction 1600, Right 500, Drop 400, Down 50, Over"

This would indicate a OT direction of 1600 mils, and a shift 500 meters right, 400 meters closer to the observer, and 50 meters down in altitude from the known point

"Direction 1600, Right 500, Drop 400, Down 50, Out."

Target Description

Lastly, the FO will provide as complete a target description as possible to ensure the FDC has a clear picture of what they are engaging.

"Platoon of infantry, dug in trenches, length 400, attitude 1200, Over."
"Platoon of infantry, dug in trenches, length 400, attitude 1200, Out." 

Additional Requests

The third transmission is where the FO can add requests to how the target is engaged, once the description is given. Some common examples include

A target on the back side of a hill from the firing unit is an example of when to use high angle, as a lower trajectory is likely to impact short.

High Angle

  • Indicated that the trajectory of the round will be a higher arc, plunging the round down into the target. Useful for targets close to tall obstacles such as treelines, ridges, or buildings. Time of flight will be significantly higher.

Danger Close

  • Indicates target is within 600 meters of friendlies. Care should be taken to alert friendlies to incoming rounds.


  • Requests a specific type of round (HE, ICM, Smoke, GPS) to be used.


  • Requests a specific fuze for the round (Impact/Quick/Point Detonate, Delay, Time, Proximity/VT)


  • Requests a specific pattern of impacts or "sheaf" the guns will orient on. Standard is usually Circular or Parallel. Open indicated a more spread out pattern, where Converged means a tighter more concentrated sheaf.

At My Command

  • By default missions will be fired as soon as ready by the firing unit. At my command indicates the FO will call ("Cancel At My Command") when the mission is to be fired.

Time on Target

  • Requests the mission be fired at a specific time, either from the time the call for fire is recieved ("TOT 10 Minutes from now"), or at a specific time (TOT 1430 ).

Continuous Illum

  • Fires illumination rounds at specified target, by default at an interval determined by the FDC to match the burn-out time on the illum rounds, to ensure constant illumination of the target area.

Message to Observer (MTO)

The message to observer is given from the FDC to the FO once a complete call for fire has been received. The MTO serves to inform the observer the manner in which the target will be engaged, and any changes to the observer's requests. Just like a call for fire, the FO is expected to repeat the MTO back to the FDC to ensure all data is correct. The MTO can vary depending on the situation but will always include the number of rounds and target number. Additional information may passed as requested by the FO in the call for fire.

Units to Fire

Indicates the call-signs of units firing.

"...<battery callsign>..."

Changes to FO Requests

Indicates any changes to requests. For example, if the FO requested ICM, but the FDC decided to engage with HE with a Proximity Fuze, the MTO would include

"...HE Proximity in Effect..." 

indicating the fire-for-effect phase will use HE/PROX instead of ICM

Number of Rounds (and number of guns)

Indicates how many rounds each gun of the unit will fire (NOT the total number of rounds the unit will fire). Typically given alongside the number of guns to be firing to the total number of rounds can be determined..

"...3 Guns, 4 Rounds..."

indicating 3 guns will fire 4 rounds each for a total of 12

Target Number

Indicated the number assigned to the particular mission, extremely important both for multiple missions going on at the same time, as well as saving data for future re-engagements using the same data. FO should assign this number to a mark on the map corresponding with the location of the target, once the mission is complete.

"...Target Number 1001..."

Time of Flight

If requested in the call for fire, time of flight for the rounds is given in seconds.

"...Time of Flight 32..."

Example of a Complete MTO


"FO, this is FDC. Message to Observer. "Thunder', HE Delay in Effect, 4 Guns, 6 Rounds, Target Number 1003, Time of Flight 15, Over."


"FDC, FO. "Thunder', HE Delay in Effect, 4 Guns, 6 Rounds, Target Number 1003, Time of Flight 15. OT Direction 1600. Out."

Note the FO includes the OT direction to the target if it has not been given in the call for fire, regardless of target location method. This direction will be required for the follow on adjustment phase.

Observing and Adjusting Fire

Spot what you see, adjust what you spot.

The process of observing the impacts of a fire mission and adjusting the fire onto target is the majority of what an FO does. The faster and more accurately the FO can adjust, the more likely the fires are likely to achieve their intended effect at a lower amount of ammunition consumption. A FO should always strive for first-round fire-for-effect, or having the first adjusting round land on target and immediately moving to a fire-for-effect. However, as is often the case, adjustments must be made in order to get full effect on target.

All adjustments are made along the Observer-Target (OT) Line, the imaginary line between the observer and his target. This is why the FDC requires the OT direction if it is not given, even in a grid mission.

A firing unit will inform the observer when each adjusting round is fired. Transmitting "Shot" followed by the target number. As always, the FO will acknowledge this by repeating it back to the FDC.

"Shot, Target Number 1001, Over."
"Shot, Out."

Approximately 10 seconds before impact, the FDC will call "splash" to indicate to the FO impact is imminent, and inform the FO to prepare to spot the impact.

"Splash, Over."
"Splash, Out."

Height of Burst

The altitude of the burst, or height of burst, typically only applies to time-fuzed rounds (such as Illum or ICM). Proximity rounds, while bursting in the air, are not adjustable and always explode at a set height above the terrain. Adjustments to the altitude of the burst are made either UP or DOWN in meters.

"...Up 50..."


Range, or how far along the OT Line the next round needs to be adjusted, either ADD or DROP in meters. Range estimation is the most difficult part of spotting, but can be expedited with a technique known as Bracketing.

"...Drop 200..."


Bracketing is the process of observing the impact of a round, and attempting to place the next round on the opposite side of the target from where the first round landed (i.e. if the round landed short, the next round should land long). This establishes a "bracket" or a known envelope that the target must lie.

For example, if we estimate the range at 2000 meters, and the first round lands long, the subsequent adjustment might be to drop 400 meters. If the next round lands short, we know the target lies somewhere between 1600 and 2000 meters.

Example of successive bracketing.
  • Successive Bracketing

his process is repeated, halving the distance of the adjustment each time, attempting to get the next round to land opposite the target from the previous round, further narrowing the envelope until range is correct. This is known as Successive Bracketing, and allows the observer to use the minimum amount of rounds possible to achieve the correct range. It is particularly useful the further out the target is from the observer, where range estimation become more difficult. Key to this concept is making bold adjustments, depending on estimated range.

  • Hasty Bracketing

Another alternative is a Hasty Bracket. Once the initial bracket is established, the observer uses the known envelope as a "yardstick" and attempts to locate the target's range faster by estimating where the target is in the envelope instead of trying to adjust long and short until on target. This depends heavily on the observer's ability to estimate, but can achieve on target effects faster than successive bracketing.

  • Creeping Fire

Used typically when calling in danger close missions, creeping fire adjusts the impact of rounds closer and closer to the observer by small increments in order to avoid placing rounds on friendly units.


Deviation is the lateral adjustment of fire, either LEFT or RIGHT of the OT Line in meters. Using optics with a mil-reticle pattern, or a compass, deviation can be quickly adjusted for using the Mil-Relation Formula.

"...Left 160..."
An impact measured 50 mils right of the intended target. With an OT factor of 1, the adjustment to the firing unit would be LEFT 50.

Calculating Deviation

  1. An OT Factor is calculated by simply taking the range to target in meters and dividing it by 1000 then rounding to the nearest whole number. For example for a target at 3250 meters, the OT factor would be 3.
  2. Using either a mil-reticle pattern, or a compass, the difference in Mils between the impact and the target is calculated. Also note what side of the OT Line the impact was (left or right)
  3. Multiply the difference in mils by the OT factor to find the adjustment needed in meters.
  4. Ensure you are adjusting the correct direction towards the target, not what side the target the impact landed. (i.e. an impact on the right side would adjust to the left)

Transmitting Adjustments

Once all spottings have been made for an impact and adjustments calculated, the FO is ready to transmit to the FDC their adjustment. If multiple missions are occurring, the FO may transmit the target number before adjustments to avoid confusion. The order of adjustments transmitted is Deviation, Range, then HOB.

"Right 50, Add 400, Down 70, Over."
"Right 50, Add 400, Rowniowngh0t 70, Out."

Fire for Effect

This process is repeated until impacts are within effects range to the target, typically 50 meters for HE. Once on target, the FO will call for "Fire for effect" indicating the rest of the guns involved in the mission will fire on the last adjustment made.

"Left 50, Drop 50, Fire for Effect, Over."
"Left 50, Drop 50, Fire for Effect, Out."

The firing unit will call "Rounds complete", once the last round has been fired (not when the last round impacts).

"Rounds Complete, Over."
"Rounds Complete, Out."

Further Adjustments, Recording Target, Ending Mission

Depending on the outcome of the mission, the FO may choose to simply end the mission.and provide a BDA

"End of Mission, Tank Destroyed, Over."

Or record the target for further use later.

"Record as Target, End of Mission, Over."

They may wish to repeat the mission using the same data.

"Repeat, Over"

Or make adjustments before repeating.

"Left 50, Add 100, Repeat, Over."

Several other adjustments can be made, depending on the situation.

Check Firing

If at any point unsafe firing or danger to friendlies is imminent, "Check Firing" should be transmitted to the firing unit(s). Upon receipt of check firing all units will immediately cease firing regardless of status until "Cancel check firing" is received.

"Check Firing! Check Firing! Check Firing!"
"<unit callsign> Roger, Check Firing, Out."

Fire Planning

Along with locating and engaging targets on the battlefield, the FO should assist the commander in fire support planning in order to reduce the time needed to engage likely enemy positions and to best support the maneuver elements. Predicting where the enemy will be, and having prepared fire missions can disrupt the enemy's plan and their ability to maneuver, in addition to causing casualties. Both in the attack and defense, fire support must be planned with the mission in mind, and ensure that they support the commanders intent.

Below is and example of an AO with several likely enemy locations, and the best way to engage them. Keep in mind the map may not provide the complete picture, and on-the-ground reconnaissance is always recommended.

An example AO and possible fire plan locations.

TRPs vs Targets

A common mistake is treating Target-Reference Points as pre-planned targets. A TRP represents an easily identifiable terrain feature that can be used to direct attention to, or adjust from. TRPs make excellent Known Points for Shift fire missions. Targets are pre-planned grid locations that are intended to be fired at, they are not required to be easily identified on the ground, a requirement of TRPs.

  • A good TRP would be a sharp hilltop, monument, tower, or intersection.
  • A good target is a ditch likely to conceal the enemy. or a treeline within the axis of advance
Example of Targets in red (defilade the enemy will likely retreat into) and TRPs in black (Easily recognizable hills and compounds) note different numbering to avoid confusion.

References and Links

FM 6-30 Tactics, Techniques, and Procedures for Observed Fire