Defending theory - UNITAF Force Manual (FM)

FM/G238 - Defending theory

Guide

FM/BG-1119 - Principles of defending

Guide

Security: Observation of all avenues of approach must be maintained. Sentries, OPs, and rear/flank watch are essential. Without 360° awareness, the defense is vulnerable to surprise and flanking.
Positioning: Every position should offer cover from fire, concealment from observation, and effective fields of fire. Terrain and fortifications must be used to the defender’s advantage, while minimizing exposure to likely threat angles.
Depth: A layered defense absorbs shocks and enables fallback. Forward elements slow the enemy, while reserves counterattack or hold rear lines. Depth provides both resilience and flexibility.
Mutual Support: Defensive positions must overlap in fields of fire, allowing them to support one another. No position should be isolated; any attack on one should trigger fire from others.
Flexibility: Plans must account for contingencies. Have fallback positions, repositioning routes, and mobile reserves. Defenses that cannot adapt are easily overrun.

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FM/BG-1120 - Applying OCOKA in defence

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Observation & Fields of Fire

Position weapons to cover expected approaches with interlocking fire
Use elevation and open terrain for long sightlines
Assign sectors and clear kill zones of obstruction

Cover & Concealment

Select terrain that offers protection and concealment
Use fortifications and camouflage to reduce visibility
Prepare alternate firing positions

Obstacles

Use terrain, wire, or mines to channel enemy movement
Cover obstacles with direct or indirect fire
Avoid blocking friendly fields of fire

Key or Decisive Terrain

Hold terrain that controls movement or offers advantage (e.g. high ground)
Reinforce positions likely to be attacked
Use terrain to protect flanks and enable movement

Avenues of Approach

Identify all likely enemy routes
Funnel the enemy into kill zones
Maintain security on flanks and rear

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FM/BG-1121 - Linear defence

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Linear defences align perpendicular to the expected enemy approach. They excel in chokepoints and with limited flanking risk. Strengths include strong frontal firepower and simplicity. Ensure flank security and avoid using this setup against mechanized threats unless terrain supports it.

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FM/BG-1122 - Perimeter defence

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Used when threats may come from multiple directions or when isolated. Forces are arranged in a loop or triangle, using all available cover. Squad-level perimeter defences are vulnerable, platoon-scale is more effective. Ideal for holding terrain without a defined enemy axis of advance.

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FM/BG-1123 - Reverse slope defence

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Position defenders on the side of a hill opposite the enemy. This limits enemy observation and firepower until they crest. Benefits include protection from direct fire and artillery, but it requires forward observers and a plan for difficult withdrawals. If possible, include a rear slope security element.

Above: Visual representation of reverse slope defence

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FM/BG-1124 - Urban or strongpoint defence

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Urban defences combine linear and perimeter features. Key considerations:

Dominate streets and choke points with MGs and snipers.
Establish fall-back positions for fluid defence.
Support vehicles with infantry, especially in close quarters.
Use observers in tall buildings, but avoid obvious or predictable locations.
Disperse units between buildings to reduce explosive casualties.

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FM/BG-1125 - Spoiling attack

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A spoiling attack disrupts the enemy’s plans by launching a surprise counterattack from defensive positions. Best conducted with armor or small infantry raids, it can fracture enemy cohesion. Only attempt if the force can afford the risk and spare the assets.