The Complications of Structures in the Urban Fight (Part V of a series)

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This is the fifth article of a series on the Twelve Urban Challenges. You can access the series here

The very idea of a city is asymmetric, yet simple – perimeter walls that allow modest forces to resist powerful armies.  Previous articles have examined perceptions of the urban fight, this one examines the four challenges of the physical environment that make the fight in and amongst walls invariably difficult and complicated. 

Complication comes from the walls within that constrict manoeuvre, attenuate combat power and give further advantage to defenders.  In AD 70, Flavius’ professional legions were repeatedly ambushed and repulsed on the narrow streets of Jerusalem by untrained Zealots throwing rocks from above. In 2017, in the largely evacuated city of Marawi, Islamist militants held off the Philippines military for months – with handheld weapons and improvised explosive devices.

Such complication is always present in an urban area, regardless of whether an overlay of factors of population and politics make the fight truly complex. The challenges of structures are: hands-off attack, concealment and ambiguity, aggravated exposure, diluted combat power and degraded technology.

Physical Terrain: Four Enduring Complications

Challenge three – Hands-off Attack is the increased scope amongst urban structures for the engagement of forces using weapons displaced in time or space from the operator. It ranges from use of mines and Improvised Explosive Devices (IED) triggered by their targets, through remote triggering of explosive devices, to now include remotely controlled or autonomous drones or weapon stations. New and sophisticated systems are dramatically decreasing the vulnerability and increase the combat power of individual adversaries.

While hands-off attacks are executed in all environments, the urban environment channels people and vehicles through predictable nodes, greatly increasing the probability of a single weapon inflicting casualties.  Furthermore, urban structures typically offer a variety of opportunities to site both weapons and triggering systems: fabricated items are far harder to hide in nature. Adversaries also have far more scope to find concealed and protected positions from which to observe and control devices than in a natural environment.

The threat from hands-off attack in urban areas is steadily increasing. While self-activated explosive devices have existed for centuries, urban use of mines and booby-traps first became widespread during World War II.  Basic radio and infra-red triggering was introduced by the PIRA, ETA and other terrorist groups in Europe in the 1970s and was adopted by insurgent groups for urban combat, for example in the Tamil Tiger 1987 defence of Jaffna against Indian forces. 

After the 2003 invasion, Coalition forces and resistance movements quickly entered an arms race of IEDs versus countermeasures. Insurgent designs progressed from radio initiation, through mobile phones to triggering by US countermeasure ‘jammers’. Similarly, armour defeating warhead designs spread out from the ‘training school of Iraq’ and were refined for use in increasingly sophisticated multiple ambushes.

The technology can be considered mature and in recent urban battles, insurgents have made IEDs their principal killing weapon, turning every building into a potential minefield requiring deliberate cautious clearance and largely accounting for the protracted nature of the fight. 

Adversaries have been adapting commercial drones with sacrificial explosive payloads or to drop grenades, and while still relatively crude, during the battle of Mosul, the threat from them repeatedly stopped the Iraqi forces from advancing. In similar vein, remote control weapon systems for small arms and missile launchers above ground, controlled from bunkers below ground, were encountered by the Israelis in their 2006 operations against Hezbollah.

A variety of such improvised remote-control stations for small arms and rocket launchers have been deployed in urban areas by insurgents in northern Iraq and Syria. Neither these systems nor the armed drones used by insurgents approach the precision capabilities of those currently being produced by specialist manufacturers – when true precision weapons reach insurgents the hands-off threat can be expected to dramatically increase the risk of all exposed movement and further slow urban operations.

Challenge four – Concealment and Ambiguity gives the adversary relative freedom of manoeuvre and insulation from effective intelligence, surveillance or reconnaissance amongst urban structures, infrastructure and population. 

Buildings and structures not only hide everything beyond them from direct line of sight, but also screen overhead from satellite imagery, aircraft and UAV sensors. No in-service technology has the capacity to scan the interiors of large numbers of buildings for hidden adversaries, and when humans are detected it is frequently impossible to distinguish between combatants and civilians.

If adversaries cut mouseholes within interconnecting buildings and construct tunnels between more exposed structures they are able to move protected and unseen. Even without such preparation, the close packed buildings found in much of our region provide the means to conduct ‘hit and run’ attacks. 

The urban fabric allows adversaries to deceive or achieve surprise in time and place or method of engagement, especially against an advancing force that is too small to both clear and hold the area it is operating in.  Relatively untrained adversary forces may be concentrated and suddenly emerge, mount ambushes or assaults and then withdraw with support and logistic elements being particularly attractive targets. 

Ambiguity is compounded in an urban area because not only can adversaries conceal themselves effectively, but urban areas are particularly well suited for deception as ‘ground truthing’ can often only be achieved by human reconnaissance. 

Challenge five – Aggravated Exposure is the dramatically increased exposure to attack throughout an urban area and from vantage points in three dimensions that may be at close range, protected and/or defiladed.  

This challenge occurs because the presence of urban structures dictate that available routes are limited, converge at predictable nodes and usually have little cover. Troops often must move on the street, where they can typically not only be easily observed from vantage points but attacked in three dimensions – with fire and explosive attack coming from above and below as well as horizontally.

The effect of aggravated exposure is magnified because walls and the apertures within them provide a defender with a constant series of defilade positions. The adversary can select a position within or behind a structure covering the route of advance and is then able to engage the first vehicles or soldiers that appear whilst unseen and invulnerable to those following behind. It is difficult for advancing forces to avoid the exposure of movement on streets by advancing within buildings. If doorways or passageways are available for this purpose, they themselves become choke points that impose aggravated exposure – a small number of mines and IED can be expected to cause many casualties.

The relative advantage provided to defenders by aggravated exposure on streets and within buildings can enable even untrained and ill-equipped troops that can, if willing to resist, impose heavy casualties, extended delay or require a systematic use of heavy firepower.       

Challenge six – Diluted Combat Power is the reduction in the ability to apply force and manoeuvre amongst a matrix of cellular structures because of:

  • the channelling and slowing of movement
  • the isolating and blinding of personnel
  • the masking and absorbing of weapons effects
  • the personnel consumption of clearing and securing. 

Urban areas can be imagined as a ‘cellular aggregation’ with the closed boxes that are formed by rooms assembled to form buildings, and then streets and blocks. All these structures, whether built adjacent to one another or with space between, channel soldiers and vehicles.  External movement is channelled predictably around buildings, usually to conform with a street matrix, while internal movement is similarly shaped through doors, corridors, and staircases. There are acute risks if this is not undertaken slowly and cautiously.

As troops move amongst buildings they no longer have line of sight with friendly elements behind them or to their flanks. This isolates them from support, an effect that increases even more on entering buildings, dictating that soldiers indoors will often fight whoever they encounter alone and unseen by their peers.  The supporting fire from various systems that would be normal in rural areas often cannot be applied – those who would otherwise provide support are blind to what is occurring.

The effects of supporting fire are also greatly reduced. Both direct and indirect fire projectiles are obstructed by walls roofs and ceilings. Even where structures are flimsy, small arms fire will often not penetrate beyond one or two walls, and the blast and fragmentation from explosive projectiles is similarly confined and degraded.

Suppression with direct fire weapons can often simply not be achieved, and far greater quantities of explosive munitions are required to achieve suppressive effects compared to open terrain. Adversaries within substantial concrete or ashlar stone buildings may be effectively immune to all but the largest explosive projectiles.

The cellular matrix of an urban area creates a massive clearing and securing challenge for attacking forces. The rooms, corridors, spaces and cellars within objective buildings must all be individually dealt with. Even when explosive munitions can be used extensively, systematic subsequent clearance is necessary, and this takes time and numbers. Furthermore, every room and space across an urban area represents a potential opportunity for an adversary to hide and emerge to ambush.

While detailed clearing of the many tens of thousands of rooms across every building in an area may not be feasible, it is likely to be essential to clear and secure large areas in detail, especially buildings that flank routes of advance. The gruelling process of clearance will exhaust troops and the need to leave security parties behind to secure the ground cleared very rapidly will consume a substantial force. This will often limit the scope of offensive operations.

Challenge seven – Degraded Technology is the reduction in the effectiveness of sensors, communications equipment and advanced weapons because of physical obstruction and visual obscuration as well as electro-magnetic spectrum effects including absorption, reflection and noise.

As identified earlier, one of the reasons for adversaries defending on urban terrain is that the sensors, particularly overhead sensors, available to a modern force are far less effective because of the shielding provided by urban fabric. However, there are further effects in electromagnetically dense areas.

Communication systems are disrupted by absorption and reflection from urban structures, compounded by spectrum management issues arising because more force elements are concentrated in a smaller space as well as interference from power and communication systems that are still running in the city. Once within buildings or subterranean spaces most communication systems and GPS-based technologies simply no longer work.

The challenges of hands-off attack, concealment and ambiguity, aggravated exposure, diluted combat power and degraded technology are what makes urban combat complicated. The fight becomes truly complex, meaning resistant to analysis, because of the presence of people and politics. We will explore this in the next article.

About the author: About the author: Dr Charles Knight researches capability for operations amongst populations and structures at UNSW and CSU.  An example of his field-based research is this Marawi report for ASPI. He has a practitioner and unconventional warfare background having served in the UK military and other armed forces. He also wrote the Australian urban doctrine and as a reservist is the SO1 Urban Operations at the Australian Army Research Centre. Views expressed are his own. You can follow him on Twitter @ChasAHKnight