Defending theory - Field Leadership - United Task Force (UNITAF) Arma 3

P1-100 Defending theory

UNITAF / Arma 3 / Field Leadership Procedures

Version 1 / 16min read / Updated Sun 08 May 2022 / 1009 views / of verified

Defending can take many forms. An element may be tasked with protecting something important, such as a building, key road or intersection, vehicle, or high-value personnel. It may also simply need to protect itself while in a static position. A defense can be hasty, with units rapidly taking positions in an unprepared area, or deliberate, in which special defensive obstacles, bunkers, sandbag walls, etc, can be deployed in advance of any attack.

Whatever the case may be, there are several common themes to defending successfully.


Principles of Defending


A defense will fail utterly if security is not established and maintained at all times. Security comes in the form of ensuring that the defensive positions can observe all around the defensive location and cover all possible avenues of approach. Security is further enhanced by having personnel in forward observation positions or positioned on high structures from which they can see more clearly around the defensive position.



When given an area to defend, it is up to the leaders as well as individual players to pick positions to fight from that make them hard targets. This is accomplished by taking advantage of every aspect of natural and artificial cover and concealment, as well as deploying obstacles and defensive structures to enhance and otherwise augment the existing terrain. Every fighting position should be chosen to minimize exposure to enemy observation and fires, while maximizing the lethality of the player fighting from that position.

Many defensive missions will give the defending force some flexibility in where they deploy themselves, making this a very important consideration for leaders. An area as small as 400 meters in diameter may have potential defensive emplacements that range from "Great" to "Utterly dismal", and being able to identify which is which is a critical skill to develop.



Spreading a defending force thinly over a long frontage, with no reserve and no depth to the defense, is tactically unsound. Defenders must ensure that they have depth to their defense.

This depth allows for a number of things, as follow:

  • Forward units can displace to the rear if their original positions become untenable, with their movement being covered by units who are positioned behind the bleeding edge of the front line.
  • Ensures that an enemy force will have to work hard to get a penetration of friendly defensive positions. They may overrun the first line only to be mowed down by a second line that can now place fire precisely on the locations where their former teammates had been positioned.
  • An enemy that penetrates part of the first line of a defense may find themselves trapped in a pocket, as the flanking positions and second line of defense focus their fires on them from three sides at once.


Mutual support

Mutual support occurs when positions are able to fire in support of other nearby positions. The ultimate goal of mutual support is to make it impossible for the enemy to attack one position in isolation - instead, they will always find themselves engaged by a supporting position, forcing them to attempt to attack both positions at the same time, which dilutes their efforts.

For instance, a frontal attack on one position may run into the flanking fires of a second position. Mutual support makes it very difficult for the enemy to concentrate on a single defensive position, because if they do so, they will be cut to pieces by the supporting positions.



Flexibility is a key part of a successful defense. Particularly when defending large areas, defenders can't hope to mass their defensive power all along the areas that can potentially be attacked. Flexibility is facilitated by a comprehensive understanding of the defensive position, the dispositions of friendly forces, and the creation of primary as well as secondary and even tertiary fighting positions. In an ideal situation, each defensive position has an alternate position to fight from, as well as "fall-back" positions which are deeper in the defended areas. Flexibility can also be enhanced by detaching a 'reserve' of players that will stay away from the forward defenses and wait to reinforce any area that may later need help.

Flexibility allows a defense to be able to:

  • Shift positions and angles of coverage in response to enemy attacks, placing themselves where they need to be to best defeat the enemy. 
  • Fall back to inner perimeters on demand without losing cohesion.
  • Prevent the enemy from effectively fixing them in one static position for the duration of a fight.



OCOKA in the Defense

To conduct a successful defense, one must be able to 'read' the terrain and integrate it into the defensive plans. Knowing the terrain allows for a commander to place his defenses in a fashion that will maximize the natural and artificial aspects of the environment in his favor. An experienced commander should be able to look at a section of terrain and see the positive and negative aspects of defending any given area. It is up to him to pick the best slice of terrain to defend and ensure that all subordinate leaders and units take maximum advantage of all the favorable aspects of said terrain.


Aspects to Consider

Observation & Fields of Fire

  • Be able to observe approach routes.
    • Place observation posts or scouts to watch the surrounding terrain, flanks, and the rear of the defensive positions.
    • Knowing in advance that the enemy is trying to flank or is approaching from an unexpected position gives the defenders time to shift their positions or fields of fire if necessary to react to the enemy maneuvers.
    • Observation personnel should have a plan on how to leave their observation post and make it back to friendly lines before the enemy cuts them off.
  • Fields of fire need to interlock and provide mutual support.
    • Creating mutually supporting defensive positions is very important!
    • Mutual support tends to force the enemy to attack multiple defensive positions at once, thinning out his numbers and preventing him from massing overwhelming combat power on any one point.


Cover & Concealment

  • Use both natural and artificial cover and concealment as much as possible.
    • A good defense does not reveal all of its secrets once the enemy is able to observe the defended area.
    • Keeping key weapons out of view, via concealment or cover, can allow for surprise to be achieved when the enemy attacks and unexpectedly runs into the fires of such weapons.
    • Concealment may not stop bullets, but if the enemy never realizes that fire is coming from it, it won't need to. Good concealed positions can wreak havoc on enemy attacks, particularly when firing across the flank of the attacking forces.
    • Good cover & concealment helps to lessen the effects of enemy prep fires or base-of-fire elements.
  • Make good use of enterable buildings.
    • Buildings are generally good protection during an Arma firefight, and ones with multiple floors allow for defenders to get views all around, from multiple heights, with a variety of firing apertures (windows) to use to shoot from and lessen their predictability.
    • When employing buildings, ensure that everyone doesn't simply pile into the same building - multiple buildings, supporting each other, are far more effective.
  • Have methods to move from defensive position to defensive position while making use of cover and concealment throughout the route.
    • A good defensive layout will allow someone to move from one fighting position to another without ever being seen by the enemy.
    • Being able to fall back to another 'ring' of defense without exposing oneself to enemy fire is likewise important.



  • Funnel the enemy via obstacle emplacement.
    • Use obstacles, mines, and friendly positioning to get the enemy to maneuver and attack in a fashion that fits your defensive plans.
  • Observe obstacles whenever possible.
    • Observation is done in a manner that allows friendly weapons to engage anyone attempting to move through or breach the obstacles.
    • Unobserved obstacles act as restrictions or delays to movement. They may slow someone down, but that will generally be it.
    • Observed obstacles turn areas into kill zones and produce enemy casualties.
    • The enemy, slowed down by the obstacles, becomes more vulnerable to friendly forces, which can then engage them with all manner of fires while they're attempting to traverse said obstacles.
  • Explosives are another form of obstacle.
    • The presence of obvious explosives can force attackers to reroute around them or avoid passing through a given area.
    • More subtly hidden explosives can be used to cover other obstacles as well as any gaps that might exist in the defense.
    • When observed, satchel charges are great for causing casualties on an attacking force.
    • Explosives like claymore mines, set with tripwires, can act as unobserved traps - the key point is to ensure that all friendlies are aware of their positions
    • The detonation of an explosive trap can slow the pace of the enemy's movements


Key or Decisive Terrain

  • Occupy the key terrain & high ground, or cover it by fire if occupation is not feasible.
  • Key terrain is any terrain that is likely to have an impact on the enemy's attack or your defense.
  • High ground, on the other hand, is pretty self-explanatory.
    • High ground is occupied because it places the defenders at a height advantage against the attacking forces, giving them better observation and fields of fire.
    • It is also significantly more difficult to attack up a hill than it is to fend off such an attack from on top of the hill.
  • It is important to note that defenders on high positions should not sit directly on top of the high ground but should instead be on the "military crest", which is basically any position far enough from the topographical crest that they are not silhouetted against the skyline.


Avenues of Approach

  • Identify the likely positions from which the enemy can approach or attack.
    • Position personnel to observe these approaches and cover them with fire.
    • Plot artillery or mortars, if available, to cover the most likely approaches.
  • Identify likely positions that the enemy will use for support-by-fire or base-of-fire elements and cover them accordingly.
    • Being able to identify the likely SBF/BOF positions allows for defenders to plan their positions, as well as any deployable defensive assets, more effectively.
    • Having a key weapon system like a medium or heavy machinegun pointing at a likely enemy SBF/BOF position can be decisive if they end up fighting from said position.



Types of Defenses

Linear Defense

Linear defenses are exactly what they sound like - friendly forces are arrayed in a line, perpendicular to the expected route the enemy will attack via. Linear defenses are used when the terrain favors such a defense - for instance, if terrain or obstacles such as minefields make it impossible for the enemy to bypass a given piece of terrain. A linear defense allows for friendly forces to mass firepower in one direction, with interlocking fields of fire and exceptional coverage. Linear defenses require that there are security elements posted on each flank, so that any attempts by the enemy to flank friendly positions will be seen and will be able to be reacted to. Linear defenses are also best against infantry, and weakest against any kind of mechanized enemy force which can potentially flank the position more easily than a foot-mobile force. The ideal linear defense is created such that flanking is not a viable tactic for the enemy - minefields are excellent for this, as is terrain that naturally chokepoints.


Perimeter Defense

A perimeter defense can be established in any terrain. It is utilized when the enemy can be expected to attack from a number of directions at once, or when the enemy's attack direction is not known with reasonable certainty in advance.

Perimeter defenses take advantage of any natural concealment or cover in the area. They are typically established in a triangular fashion, though it will differ based upon the size of the force and the terrain. Platoon-sized perimeter defenses are best, as they allow for a larger area to be defended, with one squad per side. Squad-level perimeter defenses are vulnerable to attack and typically end up being more of a rough circular shape than triangular, due to there being a lower number of troops to place in the defense combined with the desire to utilize all cover and concealment to the maximum extent possible.

Perimeter defenses tend to occur when friendly forces are isolated and must defend a specific piece of terrain or are just isolated in general and must defend themselves.


Reverse Slope Defense

A reverse slope defense can be a very effective form of defense if done properly. The basic principle of a reverse slope defense is that terrain is used to isolate the friendly forces from enemy fires and observation, forcing them to close with friendly forces and commit to a close-range fight where they lose many of the advantages they may have otherwise had in normal terrain.



Some benefits of the reverse slope defense are as follows.

  • The enemy cannot see friendly positions or dispositions until he crests the hill.
  • The enemy cannot use direct-fire weapons against friendly positions unless he crests the hill and exposes himself to fire.
  • Cresting the hill cuts an enemy unit off from the support of other enemy units that are still out of view of friendly forces.
  • Enemy artillery is difficult to adjust due to it being necessary to get an observer into view of friendly forces to correct the fall of the rounds.
  • The natural rise of the hill (or other high ground) may even prevent certain types of artillery from being able to hit friendly positions at all.
  • This depends largely upon how steep the hill is, as well as the location of enemy artillery.
  • Note that mortar fire will almost certainly still be able to be used in such a situation without hindrance.


There are also a few notable drawbacks that can come into play and must be considered in advance.


  • Withdrawal from a reverse-slope defensive position can be extremely difficult.
  • If the enemy establishes itself on the crest, friendly forces will be at a distinct disadvantage when trying to break contact.
  • This is one reason why having a security element on the counter-slope (terrain permitting, this is the upward-sloping terrain behind the defensive position that ends up being another hill) can be so vitally important.
  • Friendly forces in the defense cannot see past the crest of the high ground.
  • The effects of this can be lessened with proper usage of observation posts, however.


It is important that a reverse slope defense utilizes observation posts on the far side of the hill or high ground so that they can see the approach of the enemy. These observation posts can simply be a few soldiers with binoculars or scoped weapons, spread out to comprehensively cover all possible approach routes. Such observation posts should be pulled in before the attack hits, or they're apt to be cut to pieces by the enemy.

If a security element is available, and the terrain permits, it can be of great help to have the security element posted on a slope behind the main defense (known as a "counter-slope"). This allows for them to cover the flanks and rear of the main defense and engage any enemy forces that attempt to maneuver to attack in such a fashion.



Defense of a Strongpoint (Urban Environment, Village, etc)

The defense of a strongpoint can carry aspects of the perimeter or linear defense, depending on what the tactical situation is at the point being defended. Considerations for both of those defense types apply, as well as the following points.

  • Dominate the streets.
    Streets are prime killing zones, and emplacing machineguns or other heavy weapons to fire down streets can do a great deal to prevent the enemy from establishing a foothold in the engagement area.
  • Dominate all prominent choke points and integrate them into the defensive plan.
    For instance, a bridge is an excellent choke point that can be defended in strength to prevent the enemy from successfully crossing it.
  • Establish fall-back positions.
    The situation in an urban fight can change rapidly, and it is beneficial that some sort of cohesive plan be in place to allow for friendly units to fall back, establish new positions, and fight from them.
  • Use snipers, machineguns, and any kind of vehicle-mounted weapon systems to cover the most vulnerable defensive areas.
  • All armor should be supported by at least a fireteam of infantry. Armor is a massive force-multiplier in the urban defense and needs to be protected at all times.
  • Do not pile too many people into any one building.
    Buildings can be demolished, and the Arma damage model for buildings and explosives can cause more casualties to occur in such situations than you would expect.
  • Establish observer positions on tall buildings when possible.
    • If artillery support is available, they can help to call it in.
    • If not, they can scan for the approach of enemy units.
    • Try not to pick the most obvious buildings for this task - you don't have to be on a large and obvious building to be effective as an observer, and doing so will likely only help to draw enemy fire and get you killed.
    • Placing grenadiers and snipers on two- or three-story structures can also be beneficial.


The Spoiling Attack

The intent of a spoiling attack is to disrupt or "spoil" the plans of the enemy attacking force. This is typically done by the defending force by shifting from their defensive posture into an unexpected attack. If done properly the tactic can achieve an element of surprise which can contribute to the successful disruption or destruction of the enemy attacking force. Spoiling attacks are best done with armor - they can spring from their defensive positions, flank the enemy, strike hard and fast, and then withdraw back into their defensive posture.

Small infantry elements can also be used for this tactic, utilizing harassing fires via guerrilla ambushes. Done effectively, this can create confusion and disarray and lead to a breakdown in the cohesion of the enemy attack.

Spoiling attacks are only feasible if the you have the assets to spare. In many situations it will be too risky to attempt one and potentially lose those forces.

UNITAF Standard Operating procedures (SOP)
are adapted primarly from US Army Training and Doctrine Command (TRADOC). Our written and audio procedures are a combination of the following primary source materials, as well as our own learnings, modifications and adaptations:
- US Army Techniques Publication, Infantry Platoon and Squad (ATP 3-21.8)
- Soldier’s Manual of Common Tasks Warrior Leader Skills Level 2, 3, and 4 (STP 21-24-SMCT)
- The Warrior Ethos and Soldier Combat Skills (FM 3-21.75 / FM 21-75)
- Leadership Development (FM 6-22)
- Dyslexi's Tactics, Techniques, & Procedures for Arma 3 (TTP3)

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