From October 16, 2016 to January 4, 2017, US-backed Iraqi security forces conducted a full-scale city attack to liberate Mosul from the Islamic State. The operation was the largest conventional land battle since the attack on Baghdad during the US-led invasion in 2003 and one of the most destructive urban fights in modern history involving Western forces. The battle saw a force of over one hundred thousand attacking somewhere between five and twelve thousand enemy fighters defending the city. The nine-month battle is reported to have killed over ten thousand civilians, caused an estimated two billion dollars in damage to the city, created ten million tons of debris, and displaced over 1.8 million of the city’s residents.

This type of high-cost, high-risk operation—the city attack—will continue to increase in frequency unless the rules of modern urban warfare are addressed in a deliberate manner. In other words, the limitations characterizing the conduct of urban warfare must be overcome.

Modern urban warfare can entail many types of missions along the spectrum of military operations. If one were to develop a scale of urban conflict, on one extreme end would be total war. This is when two combatants, possibly near-peer militaries, wage war in urban terrain with little regard for any humanitarian laws of war or concerns about collateral damage. In total war, tactical nuclear weapons and the complete destruction of cities through aerial bombardment are both possibilities.

Sliding along the scale, next would come major city attacks during limited, non-nuclear conflict, where at least one combatant follows international humanitarian law and seeks to minimize the impact of the battle on protected populations and sites. This is where the Mosul battle falls on the spectrum.

After that would be major urban operations with limited objectives like regime change or eliminating an enemy capability coming from within an urban area, such as short-range rockets or cross-border tunneling operations. Next, would be counterinsurgency operations in urban environments where a major component of the mission is to separate a small insurgent or enemy force from the rest of the population that could number in the millions. Next would be very specific counterterrorist operations in urban areas. These usually involve intelligence-driven raids requiring speed, surprise, and highly specialized military units. The scale could continue into humanitarian assistance and disaster relief, either as defense support to civil authorities domestically or as part of broader stability and security operations in cities around the world.

Each potential urban operation varies greatly from the others in terms of the political objective, military mission, constraints on military force, time, enemy, and especially environment. With respect to this last variable, urban environments can be extremely dense or relatively spread out. They can also vary greatly from permissive to nonpermissive. A permissive environment is one where host-nation security forces have control of the area, as well as the intent and capability to assist during military operations. A nonpermissive or hostile environment is one where the host government does not have the will or ability to help in a military operation, or lacks control of the territory or population. A military must approach a hostile urban environment with the assumption that threats can come from any direction or domain (to include from underground).

The city attack is a very specific type of military operation—although the phrase is not US military terminology. Such a planned operation would be doctrinally classified as a deliberate attack with one of five distinct forms of maneuver, such as penetration or envelopment. In simple terms, a city attack is a mission to either kill or capture all hostile forces (an enemy-based mission) in a city or to seize, secure, recapture, or liberate (a terrain-based mission) a city or portion of a city when the enemy is using it as a defensive zone. The city attack operation usually requires a penetration of enemy defenses.

Recent historical examples of city attacks in limited warfare where an attacking force attempted to kill the defenders or seize the city include:

Hue, Vietnam: January 31 1968 to March 3, 1968
Vukovar, Croatia: August 25, 1991 to November 18, 1991
Sarajevo, Bosnia and Herzegovina: April 5, 1992 to 29 February 29, 1996
Grozny, Chechnya: December 31, 1994 to February 8, 1995
Grozny, Chechnya: December 25, 1999 to February 6, 2000
Fallujah, Iraq: April 4, 2004 to May 1, 2004
Fallujah, Iraq: November 7, 2004 to December 23, 2004

Military operations against enemy-held cities have become increasingly frequent. In the last eight years, there have been twelve distinct major urban battles involving city attacks. These have occurred in the ongoing civil war in Syria; against the Islamic State in Iraq, Syria, and the Philippines; and between government and Russian-backed separatist forces in eastern Ukraine. Among the most recent examples are:

Aleppo, Syria: July 19, 2012 to December 22, 2016
Ghouta, Syria: April 7, 2013 to April 14, 2018
Deir ez-Zor, Syria: July 14, 2014 to September 10, 2017
Ilovaisk, Ukraine: August 7, 2014 to September 2, 2014
Kobani, Syria: September 13, 2014 to January 26, 2015
Debal’tseve, Ukraine: January 14, 2015 to February 20, 2015
Ramadi, Iraq: August 11, 2015 to February 9, 2016
Fallujah, Iraq: May 22, 2016 to June 29, 2016
Mosul, Iraq: October 16, 2016 to July 20, 2017
Raqqa, Syria: November 6, 2016 to October 17, 2017
Marawi, Philippines: May 23, 2017 – October 23, 2017
Tal Afar, Iraq: August 20, 2017 to September 2, 2017

All military operations contain risk and there are many types of risks incurred in warfare. Tactical risks, for instance, relate to the possibility of injury or death of soldiers or failure to accomplish the mission. Accidental risks include such things as the potential for the deaths of civilians or destruction of critical urban infrastructure. There are also broader risks in military operations, like the risk of losing the political will (be it domestic, regional, or international) to continue the pursuit of the military objective of liberating a city from enemy forces. Urban environments compound risks unlike any other due to the complexity of the physical terrain, the presence of civilians, and the ecosystems of political, economic, and social networks that define urban areas.

Urban warfare is also the most difficult form of warfare. And while a city attack may not be the most difficult type of urban operation—a counterinsurgency involving separating a few enemy personnel from among millions of people while maintaining a military’s legitimacy could be considered more difficult—it is one of the riskiest missions a nation can attempt. There are disproportionate levels of political, tactical, and accidental risk in attempting to liberate a city from a defending force.

Moreover, the US military does not have a guidebook for attacking a defended city. There are only a few mentions of it in doctrine. One of the few examples—US Army Field Manual 3-90-2, Reconnaissance, Security, and Tactical Enabling Tasks, Volume 2—contains five pages on large-scale offensive encirclement operations, yet this has historically been just one major component of setting the conditions for a city attack.

The closest thing to a “how to” guide for a deliberate urban attack are found in the general, doctrinally recommended phases that, problematically, are supposed to apply as much to a set of buildings as they do to an entire city. Those phases are to reconnoiter the objective, move to the objective, isolate the objective, secure a foothold, suppress the objective, execute a breach, clear the objective, consolidate and reorganize, and prepare for future operations.

Some will argue that the absence of instructions on how to conduct a city attack is because doctrine is not meant to be descriptive. They might say this despite the presence of operation-specific doctrine like the counterinsurgency operations manual for which an abundance of work done in the 2000s to update and produce. They will also argue that the principles, characteristics, or general considerations for any deliberate attack will apply to a city attack just as it would in open terrain. To be sure, many of those principles and considerations do apply to all environments but the requirements of conducting a deliberate attack in a city are worlds apart from doing the same operation in wooded terrain.

Another justification for the lack of a single, doctrinal guide to the city attack mission is that much of the knowledge is spread out across many different manuals. The city attack is a large-scale combat operation requiring a full suite of combined arms and enabling capabilities—tanks; infantry; artillery; attack aviation; intelligence, surveillance, reconnaissance; and more—which are necessarily covered in their own doctrinal publications. It can also include multiple separate events that are similarly discussed in a variety of manuals—combined arms breaches in Army Techniques Publication (ATP) 3-34.22, Engineer Operations—Brigade Combat Team and Below, for instance, or electronic warfare operations in ATP 3-12.3, Electronic Warfare Techniques.

Despite the lack of a comprehensive guide to conduct a city attack against a defending enemy, there is a discernible set of conditions that have remained constant across modern history. These conditions could be considered the rules of the game for a city attack. The use of the word “game” is not intended to simplify the complexity or downplay the significance of war. In his seminal work, On War, the Prussian military theorist Carl von Clausewitz wrote, “In the whole range of human activities, war most closely resembles a game of cards.” He further described war as “nothing but a duel on a larger scale. Countless duels go to make up war, but a picture of it as a whole can be formed by imagining a pair of wrestlers. Each tries through physical force to compel the other to do his will; his immediate aim is to throw his opponent in order to make him incapable of further resistance.”

Modern urban warfare resembles more a mixed martial arts fight than either the game of cards or wrestling Clausewitz chose for his analogies. But warfare and games are bound by a set of rules that both players agree to consciously or unconsciously follow. In war, these rules are not just normative or legal ones governing the conduct of military operations; they can also be imposed by the limits of human performance or weapons technology or by the evolutionary progress of strategies and tactics of the time.

Throughout history, militaries and societies have changed the rules of the game with new organizational models, tactics, technologies, and weapons. When these changes are sufficiently transformational, military scholars call them revolutions in military affairs (RMAs). Examples of RMAs (or changes that led to RMAs) include the introduction of the longbow, gunpowder, and fortress architecture; Napoleonic warfare’s strategy of battlefield annihilation of enemy armed forces and its levée en masse to create and sustain large nationalistic armies; Industrial Revolution changes that made it possible to feed, arm, and move military forces and mass them for battle; and the twentieth-century introduction and refinement of combined arms tactics, blitzkrieg operations, and strategic bombing.  

Arguably one of the most relevant modern military revolutions, besides the invention of nuclear weapons, was the incorporation of battlefield lessons learned, new technologies, and combined arms breakthrough tactics by the German military from World War I through World War II. By joining the tank, radio, airplane, artillery, and rapid breakthrough tactics, the German military made the positional tactics of trench warfare of World War I much less of an advantage to defending militaries. The German military, in essence, changed the rules.

Urban warfare has its own rules. In large-scale combat operations to liberate an enemy city today, those are rules that most if not all militaries have allowed to remain in place since World War II. These rules give great advantages to a defending force and make it an attractive option for militaries, insurgents, and terrorists who are weaker than their opponents. Until these game rules are changed (through a major change in tactics, technology, or weapons), the tendency of comparatively weaker actors seeking refuge and advantage in cities—and the damage caused in their liberation—will only continue.

The “rules” of city attacks define the character of urban warfare today. They are:

1. The urban defender has the advantage.

This rule is first among equals. Military theorists have long recognized that the defense is the stronger tactical position. It takes much more force to attack and defeat an enemy that is in an established and properly constructed defense than one in the open. This is even more so in urban terrain where many of the physical structures offer immediate military-quality defensive positions for the defender.

But the defense is also recognized as a weaker position that a combatant is compelled to execute because it is not strong enough to offensively attack the other side. The defense is meant to hold terrain or preserve forces. As long as the defense provides a weaker force measurable advantages to get to a piece of terrain first and then establish a defense, it will do so.

The degree of advantage held by the defense has ebbed and flowed across history, however. For much of ancient history and up until to the nineteenth century, defending from behind walls—whether in cities, castles, or purpose-built star-shaped fortresses—provided massive advantages. The defenders could stockpile resources inside the walls and wait out the siege force or establish killing fields in which attacking troops could be targeted from atop the walls. But the evolution of advanced siege tactics, gunpowder, and ultimately rifled artillery caused the strategy of defending from behind walls to all but disappear from war.

In World War I, the positional character of warfare across Europe led combatants to adopt a strategy of moving forward of valuable terrain, including vital urban areas, to establish trench lines and killing fields covered by machine guns and artillery. Attackers had to cross these killing fields to gain terrain. With the evolution of maneuver warfare and new technologies such as the tank, airplane, and improved military communications, the advantages of occupying a trench-line defense were substantially negated and was seen less.

Today, the advantages provided to a weaker force to occupy urban terrain are great. A weaker enemy can use the physical terrain for concealment and cover both to fight from (e.g., using heavy-clad buildings as de facto military-grade defensive structures) and to maneuver (e.g., through buildings or underground in civilian infrastructure and prepared tunnels). Defending forces can also hide among the protected populations and structures outlined by the laws of armed conflict. In short, they can reduce the effectiveness of a substantial portion of present-day military technologies and tactics.

Until military tactics or technologies change to make an urban defense less advantageous to an armed force despite its objective comparative weakness, it will remain a dominant feature of the character of modern warfare.

2. The urban terrain reduces the attacker’s advantages in intelligence, surveillance, and reconnaissance, the utility of aerial assets, and the attacker’s ability to engage at distance.

While the complex physical terrain of urban areas does not negate all technological advantages of an advanced military conducting a city attack, it does reduce the effectiveness of intelligence, surveillance, reconnaissance (ISR), aerial assets, and engage-at-distance capabilities.

Modern militaries invest large portions of their budgets developing technologies to find and destroy other military forces as far away from their own troops as possible. They value technologies such as satellite and aerial reconnaissance tools, precision-guided munitions, and long-range artillery. But in dense urban terrain, many of the advantages of these and other tools developed principally for maneuver warfare in open terrain are much less effective.

For instance, in major battles in Syria and Iraq, Islamic State fighters recognized the threat of military ISR even deep inside besieged cities. As a countermeasure, they hung sheets, plastic, and other items between rooftops to allow them to move from building to building without the fear of being seen by most military aerial assets. Multi-million dollar satellites were blinded with trash strung across rooftops.

There are some technologies being advanced that would reduce the concealment advantage of an urban defender—thermal and other imagery tools, for example—but they all have limitations such as depth of penetration, visibility, scale, and costs.

3. The defender can see and engage the attacker coming, because the attacker has limited cover and concealment.

In a modern-day city attack, the biggest tactical advantage for the defending force is that it can remain hidden inside and under buildings. The corollary to this is the biggest disadvantage for the attacking force: that it can be seen and engaged by the defenders at will.

Urban defenders can hide in any of thousands of locations in the urban jungle. They can pick and choose which buildings, windows, alleyways, or sewer holes to hide in without any worry of being discovered. They can also choose the moment of contact by deciding when to attack the approaching force. Many urban defenders, like the Chechen fighters during the 1994–95 Battle of Grozny, can employ a mobile defense whereby they move small elements around interconnected firing points and ammo caches, using tunnels between positions, to defeat a superior military force. They use guerrilla tactics to attack and then disappear back into the urban terrain. And they can canalize attacking militaries to ambush sites or down roads filled with booby traps and improvised explosive devices.

The disadvantaged attackers must move along known avenues of approach—streets and alleyways—making it is nearly impossible for them to surprise the defenders. They are fully visible and vulnerable moving through the urban terrain. Despite all the technologies enjoyed by the world’s most advanced militaries, in a city attack, crossing the street can be one of the biggest risk to the lives of soldiers.

The attackers cannot target or concentrate on enemy positions until they are discovered, usually when the defenders open fire. They will not know exactly where enemy forces are until they have closed the distance and made contact with them. Many city attacks are thus really movements to contact. Furthermore, once contact is made from a specific defended position, the attacking forces are still constrained as they cannot distinguish if there are any non-combatants in the location.

There are many technologies and tactics, though, that could reduce the effect of this urban rule.

If attacking militaries could see through concrete walls at distance and scale, it would be nearly a game changer. Today, see-through-wall technologies are limited by how close an asset has to be to a wall or in terms of the scale necessary for a large operation like a city attack (e.g., based on flight time, battery life, etc.). They are also limited in what they can see through. The steel rebar support of most concrete structures prevents most forms of radar penetration.

Many militaries are investing in robotic platforms and drones that can maneuver in advance of ground forces to increase an attacker’s capability to see in and around buildings. Here, too, there are many hurdles to overcome regarding scale, costs, duration of use, and manning for these systems. A city attack is not a mission against a single building. It is an area operation potentially involving hundreds of buildings over an extended period of time. But if investments continue there could be breakthroughs for missions like city attacks.

If an attacking military could somehow make it so the defending enemy could not see attacking forces, it would also significantly change this rule. Today’s militaries may attempt to use smoke to do this, but most of the time their smoke capabilities are too limited for such a large mission. In the past, and in other environments, the US military could also rely on its night-vision technology to have an advantage, but US forces no longer “owns the night” as they once did.

That isn’t to say the US military could not create conditions where only friendly forces could see. In Toronto, Canada, fog often causes visibility in the entire city to drop to less than one hundred meters. The US Army’s newest night-vision googles can see through smoke, dust, and fog. If it could artificially create a citywide fog like that which occurs naturally in Toronto or blanket a city with smoke that doesn’t hinder breathing, these goggles would allow only friendly forces to see. They would, in effect, “own the city.”

Light manipulation could also lessen an urban defender’s ability to see and target attacking soldiers. While executing their attack plan for the Battle of Berlin in 1945, Soviet forces shined over 140 massive searchlights at the outskirts of the urban terrain while also heavily bombarding the defenders with artillery to provide cover while their soldiers crossed open areas and potential kill zones—a reduction in tactical risk. Although the fog and dust from the bombardment actually reversed the intended effect of the lights and silhouetted the attacking infantry, the idea could be explored further.

The most effective tactic to combat the vulnerability of soldiers in a city attack would be to provide them with the mobile cover provided by mechanized assets such as tanks and infantry fighting vehicles. These platforms not only protect ground soldiers but also increase the firepower they bring to a fight. Many militaries, including Russian forces in Syria, are now experimenting with semi-autonomous or remote robotic vehicles like tanks to draw the fire of urban defenders. In the future, these systems may reduce the risk to soldiers and change this rule.

Another tactic is to reduce or eliminate the exposure of attacking soldiers in streets and alleys by going through the interior walls of the buildings in a city. The Israel Defense Forces did this during urban fighting in Nablus and Balta in 2002. They now practice it routinely in urban warfare training. The tactic has merit and could be refined with technology, but also risks escalating to destructive tactics such as driving tanks and bulldozers through buildings, as happened when Israeli forces were operating in Jenin, also in 2002, which can lead to the flattening of entire blocks and produce effects similar to those of aerial bombardments.

4. Buildings serve as fortified bunkers that must be negotiated.

Once enemy forces are identified within an urban defense, either by making themselves known by attacking approaching formations or when discovered in a movement to contact or clearing operation, they must be destroyed, captured, or neutralized. Cities are full of structures that are ideal for military defense purposes. Large government, office, or industrial buildings are often made of thick, steel-reinforced concrete that make them nearly impervious to many military weapons.

An important feature of past urban battles is the presence of mini-battles over these types of buildings. During the 1942 Battle of Stalingrad, for example, there were individual fights for Pavlov’s House (actually a multi-level apartment building) and the Commissar’s House. In the 1945 Battle of Manila it was Rizal Hall at the University of the Philippines, and in the 1968 Battle of Hue it was the Citadel. In the last ten years, cities such as Raqqa, Aleppo, and Mosul contained many of these fortress-like structures that became significant problems for attacking military forces.

Each enemy-held building halts the forward movement of the attacking force. In some historical cases, just a few enemy fighters in a building—like those in Pavlov’s House—managed to bring entire divisions of mechanized infantry to a standstill.

These structures serve as the enemy’s strength. In any other environments with a defense, an attacking army would seek to avoid the enemy’s strongest positions, maneuvering around them to strike surprising blows or massing on a single position in the defensive line to bypass major fortifications. But in a large-scale city attack operation, the buildings cannot be avoided. They cannot be bypassed. Doing so would leave an enemy capable of attacking the advancing unit’s flanks and rear.

In other forms of urban warfare, the advantage of occupying a strongpoint can be negated by besieging it. Examples ranging widely from counterinsurgency and counterterrorism operations in Afghanistan to urban policing, surrounding a building and not entering it has shown success. The attacking unit surrounds the building and then issues a tactical call out, implementing what amounts to a mini-siege. However, this is not feasible for forces in a city attack that may have to deal with hundreds of enemy fortifications and must maneuver through an entire city with multiple objectives rather than dealing with a single building.

The only current option is to identify, assault, and clear enemy fortifications in dense urban terrain.

If an alternative could be created, such as covering a building or sealing an enemy inside of a building so that the attacking forces could temporarily neutralize it, this advantage to urban defenders would be lessened. The momentum or initiative could remain in the attacker’s hands. Each enemy location could be sealed off and then addressed on the attacker’s timeline.

5. Attackers must use explosive force to penetrate buildings.

With few options with which to deal with enemy fortifications encountered in a city attack, infantry forces have little choice but to use the tools available to them.

Unfortunately, in the modern era, these are few. In fact, scholars have argued that militaries had better weapons, vehicles, and training for the task during World War II than they do today. Even in Vietnam, soldiers had better tools for clearing fortified enemy structures. They had man-carried and vehicle-mounted flame throwers, tear gas, and direct-fire munitions capable of penetrating thick concrete. All of these are effective at clearing an enemy-held bunker or building without either requiring a team of soldiers to physically enter it or completely flattening it. Neither flamethrowers nor tear gas are issued or used by Western militaries in city attacks today.

The primary current methods of attacking an urban fortification are to either destroy it or prepare the building with explosive munitions and then send infantry in to enter and clear the entire building if necessary.

Some buildings can be completely destroyed with massive munitions such as five-hundred-pound bombs. But the type of building and presence of or proximity to noncombatants or protected sites may prevent the complete flattening of an enemy-held structure.

Any enemy buildings identified before ground forces get close to them can be hit by pre-planned fires using precision-guided munitions, artillery, or mortars. This often leads to what Maj. Amos Fox has dubbed the precision paradox. This refers to a scenario in which militaries can use very precise and advanced munitions to hit known enemy locations deep in dense urban terrain, far forward of their advance. But the enemy either survives the strike due to extensive fortified qualities of the structure or simply reposition to another building, sometimes through underground tunnels or pre-made holes in walls. Thus, the attacking force only destroys the city building by building while its ultimate goal, to eliminate the enemy, is not achieved. 

So, if the building cannot be flattened, infantry soldiers are sent into the structure and, by using close-quarters battle tactics, enter, clear, and engage any enemy inside. These tactics center on a battle drill—enter and clear a room or building—that was developed in the 1970s in response to a rise in situations in which terrorists captured and held hostages. The procedures rely on intelligence, speed, and surprising the enemy in a confined space.

In a city attack, the urban defender is not surprised and easily knows all the tools available to its opponent. In the 2004 Second Battle of Fallujah, enemy fighters reinforced the insides of buildings with sandbags, booby-trapped windows, doors, and roofs, and established kill zones in courtyards and the building entryways they knew the attacking forces would attempt to enter. The attacking troops took heavy casualties in the streets, in alleyways, and while attempting house-to-house clearing using close-quarters tactics. US soldiers and Marines adapted. Instead of exposing dismounted troops to clear rooms, they changed their method to one that relied extensively on tanks and indirect firepower to clear buildings. Thus, in the absence of fortification-clearing tools or tactics, they increased their use of explosive force to penetrate buildings fully.

No matter how the three primary urban fortification tools or tactics (demolish with aerial bombardment; strike with aerial munitions, tank fire, or some other explosive to reduce enemy strength inside; or send dismounted troops to clear it with close-quarters tactics) are used, they are inadequate.

Attacking soldiers left with no adequate tools will adapt, just as US troops did in Fallujah. In the 2017 Battle of Marawi, Philippine troops constructed giant slingshots (they called them angry birds) to launch grenades into second-, third-, and higher-story windows. They also dug giant trench lines reminiscent of World War I to get closer to urban fortifications. In most cases, these adaptations use weapons, tactics, and tools that are designed for other environments and other types of warfare—meaning they are suboptimal.

To alter this urban warfare rule, tactics and technologies would have to change considerably. For instance, direct-fire munitions that could accurately penetrate the thickest steel-reinforced concrete would allow dismounted troops, who are best positioned to distinguish military targets from noncombatants in the complexity of urban terrain, to target defenders from a safe location.

6. The defender maintains relative freedom of maneuver within the urban terrain.

Israeli architect and urban warfare scholar Eyal Weizman once said, “To control a city is to control the means of circulation through a city. To be able to move through it, to be able to get to everywhere you want to go, you need to keep the arteries open, or to make new arteries, by either planning or destruction or the interaction of both.”

Most city attacks come from the periphery into a point along a besieged city’s defenses. They are also primarily ground assaults. Air mobility, or the use of aircraft to insert forces, and close air support are usually limited during attacks due to the degraded ISR in dense urban terrain and vulnerability of slow and low-flying air assets, as seen during the 1993 Battle of Mogadishu.

There are military tactics that attempt to deceive the defender regarding the exact location of the main assault, which attackers employed during the 2004 Second Battle of Fallujah, successfully using information operations and small feints to make the enemy believe the attack was coming from the south of the city when in fact it came from the north. But once the main assault is committed, breaching the city defenses, the defenders can reinforce planned fortifications with mobile assault groups as Chechen fighters did to successfully defeat a major Russian formation in the First Battle of Grozny.

Urban defenders maintain freedom of movement inside their defenses. They can prepare the terrain to facilitate their movement to wherever the battle requires. They can connect battle positions with routes through and under buildings. They can construct obstacles to lure attackers unknowingly into elaborate ambushes because of the limited main avenues of approach in many dense urban environments. But, if the attackers could manipulate the terrain to their advantage during the attack, the rule would change. This is done in modern city attacks in small ways. Bridges in and out of the city can be disabled and major routes blocked by troops, but mobility inside the defense remains unfettered.

To truly change this rule, attackers would have to be able to rapidly manipulate the urban terrain to their advantage. Existing terrain such as buildings could be knocked down to isolate pockets of enemy fighters within a smaller area of the city. Some type of physical obstacles could also be emplaced deep into the city to cut it into more manageable battle areas. In the 2008 Battle of Sadr City, US forces emplaced nearly three miles of concrete walls to prevent enemy fighters from getting to vital rocket launch sites and accessing military resources they needed to fight. This was not done quickly, but the idea of redesigning the city’s flows to localize the combat does have merit.

7. The underground serves as the defender’s refugee.

Advancements in military ISR and aerial attack—despite their limitations in cities—have pushed urban warfare underground. Recent combat operations in Syria, Iraq, and eastern Ukraine have all seen a rise in the use of the underground. Defenders use existing tunnels or dig their own to connect fighting positions, hide from detection, and provide cover from aerial strikes, and even employ them offensively as tunnel bombs against stationary military forces.

Attackers in modern urban operations mostly view the underground as an obstacle to address if encountered. US Army doctrine and training overemphasizes subterranean operations like the ability to clear tunnels. There is no mention of how the presence of tunnels could be used to the attacker’s advantage—to cover movement, for instance, or to ensure surprise.

If militaries invested in and developed rapid tunnel-making capabilities, they could avoid much of the urban defender’s obstacle belts and plans. By either digging tunnels from the outside of the city or using existing urban infrastructure, an attacking force might be enabled to bypass all primary defensives and start its attack from the center of the city moving outward. It would be a modern-day Trojan horse. It would also be similar to the German response to the French Maginot Line. In May 1940, when German forces came to the long line of defensive fortifications along the two countries’ border—which the French believed was impenetrable—they simply went around the entire line. They changed the rules and the advantages of positional defensive lines of previous eras.

To be sure, digging a tunnel big enough to pass enough troops through would take time and resources. But the 2017 assault on Mosul took nine months once it started, and that does not account for planning activities ahead of the battle. The Islamic State had been allowed two years to build multiple complex defensive belts around the city. In 2014 and 2015 rebel fighters in Syria dug tunnels over three thousand feet long in just fifty days with hand tools alone. With modern technologies, digging a tunnel long enough and big enough is not unfeasible if a military would commit to the idea. While some US defense organizations are exploring rapid tunneling, it is not yet for these types of purposes.

8. Neither the attacker nor the defender can concentrate their forces against the other.

Most advanced militaries prioritize maneuver warfare. That is the type of warfare for which they train, organize, and equip. They do not prepare for positional warfare. Maneuver warfare relies primarily on the rapid and unexpected movement of formations to destroy enemy forces. A key principle of maneuver warfare operations is to mass and concentrate the effects of combat power at the most advantageous place and time to produce decisive results.

A defense established in dense urban terrain constrains both the rapid movement and the ability to concentrate formations against decisive points. This goes for both the defender and attacker. There have been a few modern examples of urban defenders with the ability to organize in disaggregated formations that combine without instructions to attack their opponents once identified. This was the case of paramilitary fighters in Somali during the 1993 Battle of Mogadishu. There have also been plenty of historical examples of militaries using swarming, engaging an adversary from all directions simultaneously, from ancient sea swarming by Greeks during the Greco-Persian Wars to Mongolian land swarms combining horses and archers in the thirteenth and fourteenth centuries.

A major evolution of tactics and technology would be required to change this rule of modern-day city attacks. Most militaries do not practice the decentralized operations required to truly implement swarming and rapid massing in an urban attack. A very broad combination of doctrinal change, risk acceptance, an instant and shared operational picture, and experimentation would be required to attempt swarming by dismounted soldiers. The combination of humans and robotics (manned/unmanned teaming) arguably holds the greatest potential for enabling swarm tactics, since it could allow rapid massing of a force that has identified any enemy strongpoint during an attack.

We Are Playing the Wrong Game

One of the reasons none of these rules of city attacks have been really explored is because modern, Western militaries, especially the US Army, is playing the wrong game. The US military is designed for maneuver warfare and the city attack is classic positional warfare, more like siege warfare fighting than something the principles of maneuver warfare call for. In fact, if the eight rules of city attacks are compared to cases of siege warfare in medieval Europe, one would see that many of the challenges are largely the same: attacking fortifications with no cover or concealment or hindered by massive defenses. But the difference is that militaries in the past adapted, developing ways to address these challenges such as using mobile cover while closing the distance to fortifications, digging tunnels under walls, employing artillery to create opening in walls, and many other innovations. 

Since modern militaries do not sufficiently understand the city attack as terrain-based positional warfare, they apply the principles, tools, and methods of enemy-based maneuver warfare that rely on maneuver and firepower. Ultimately, this fundamental misunderstanding leads to the destruction of entire cities, building by building.

If militaries fail to address these rules, the city attack will remain one of the missions with the most tactical, accidental, and political risk. It will continue to drive combat into urban areas where weaker combatants can use the advantages they gain for short-term political wins. 

If, however, the rules of urban warfare could be changed, if militaries overcame the disadvantages of attacking an urban defense and took advantages away from the defenders, warfare would move out of the cities as adversaries learned it was a quick way to be rapidly defeated.

John Spencer is chair of urban warfare studies at the Modern War Institute, co-director of MWI’s Urban Warfare Project, and host of the Urban Warfare Project Podcast. He previously served as a fellow with the chief of staff of the Army’s Strategic Studies Group. He served twenty-five years as an infantry soldier, which included two combat tours in Iraq.

Image credit: Staff Sgt. Daylena Ricks