What makes urban operations so challenging is in the name: urban. The physical terrain itself has been built and altered, whether coincidentally or intentionally, to create an extremely challenging environment with its own unique challenges for defenders and attackers. When most think of urban warfare at the tactical level, Battle Drill 6 comes to mind. A team of soldiers moving from room-to-room, violently clearing each in a savage contest of wills with an enemy only inches away in the cramped, dark confines of desolate buildings. In this mental scenario, solid planning takes a backseat while violence of action carries the day. This is not reflective of the reality of urban combat operations.
While room clearing is a facet of urban combat, it’s not always a mission requirement. A mission to destroy an enemy strong point may not require a platoon to charge through the breach full speed. A piece of key terrain in a building behind or adjacent to the enemy position could provide the direct fire capability to neutralize or suppress an enemy or could simply cut off their avenues of approach from the rear, denying them resupply or egress once their position becomes untenable, forcing them to maneuver on the friendly force instead in order to escape. Or in doctrinal terms, a turning movement. Through this, an attacker with the proper planning and understanding of the terrain can accomplish their mission without having to enter and clear a room.
The first step to executing a successful combat operation in an urban environment, just like any other operational environment around the world, is to analyze the terrain. By understanding the physical operational environment, planners can find key terrain, and use it to close with and destroy the enemy.
What is key terrain? The doctrinal answer is any piece of terrain that gives marked advantage to either side of a fight, that forces must be diverted to control, such as a hilltop overlooking an objective. However, what does key terrain look like in an urban fight? In a major city full of tall buildings, what becomes the metaphorical hilltop?
The standard evaluation tool for terrain in the US military is OAKOC, an acronym that details every major factor soldiers must consider in regard to terrain (obstacles, avenues of approach, key terrain, observation and fields of fire, and cover and concealment). While key terrain is woven into this acronym simply as one of the variables of terrain analysis, the other four are what truly determines what makes a piece of terrain key. In urban terrain especially, planners must evaluate all the factors of OAKOC before hastily slapping a key terrain marker on the map based on simple proximity and height of a building.
Obstacles
This includes reinforcing and naturally existing, both of which are prevalent in cities. In urban terrain, pre-existing obstacles most predominantly will be buildings, roads, and other civilian purpose infrastructure. This covers a wide variety of terrain, such as buildings built for luxury and decadence, or government and city infrastructure and buildings built with privacy and security in mind. Thus, the level of difficulty in entry will vary.
Buildings with little security in mind, such as flashy hotels, social venues and shopping centers are designed to have minimal obstacles to the flow of human traffic. Wide open promenades and staircases, floor to ceiling glass windows and thin decorative walls will prove little trouble to well-trained engineers with forcible entry equipment. Meanwhile, less decorative locations such as banks, federal buildings, and subterranean infrastructure often have thick walls, heavy gates, reinforced metal doors, and other security measures that in peace time keep out criminals and lost tourists.
In wartime, these protective measures become obstacles that hinder, disrupt or even defeat an attack, and make viable strong points in an urban defense. A building or subterranean complex with major defensive obstacles already in place, or easily reinforceable with concertina wire, claymores, sandbags, ponchos, or any other special defensive material, would be extremely key to an urban defender. Likewise, an attacker would value greatly from seizing that building first and denying its use to the defender or forcing them into the attack themselves.
Avenues of Approach
Avenues of approach are dictated in rural areas by streams, hills, and other natural lines of drift. In dense urban areas there is no such luxury. Most avenues of approach will be city roads, waterways and subterranean tunnels, which means canalization and compartmentalization. While this may lead many to avoid such avenues of approach to avoid ambush and gridlock, they can still be extremely key pieces of terrain in large scale combat operations.
A major intersection, or lines of communication between sections of a city, such as the Brooklyn Bridge in NYC, would be extremely key terrain because either side of the engagement could use these lines of communication as high-speed avenues of approach for mechanized, armored or logistical reinforcements, or deny that access to the enemy force.
Likewise, major tunnel systems such as the Holland Tunnel or the Subway system of NYC are extremely valuable as a means to move men, weapons and equipment without the threat of aerial surveillance platforms that are becoming more and more prevalent on the battlefield. With a predominant number of major cities being littoral, planners must also include rivers, oceans and canals as avenues of approach with the capability to recreate the Inchon landing on an entirely land focused enemy.
However, this presents a challenge, these avenues of approach are most often linear danger areas, with little to no tenable cover. The most likely course of action for any leader would be to emplace in a nearby building that can cover the key terrain, while also retaining some protection for the soldiers. Thus, key avenues of approach count doubly as key terrain. The avenue of approach itself, and the hardcover position needed to control the key terrain.
Another consideration is avenues of approach and egress from the key terrain itself. We can learn from the Azovstal steel plant during the recent battle of Mariupol in the current Russo-Ukrainian War. An extremely defensible piece of key terrain can become a death trap without an escape. In planning a defense, leaders must consider if their soldiers are able to retrograde from a building or subterranean system. They must ask how to do so safely to reach alternate and supplementary battle positions.
Observation and Fields of Fire
Being able to see and engage the enemy from distance is a critical factor in key terrain determination. An impregnable fortress, or a network of underground tunnels, is useless if it leaves a force blind. It’s counterproductive if they cannot see beyond the single block they occupy or the confines of their bunkers and tunnels. Without observation, an enemy force can easily use high speed avenues of approach to maneuver around a position. They can attack from an advantageous position, or they can bypass and isolate a unit.
This said, not every tall building with excellent observation and fields of fire should become key terrain. Isolated observation posts on top of skyscrapers are vulnerable. In cities, observation may come at the cost of protection. Mission requirements will decide whether staffs prioritize observation or security. Enemy can observe from the second floor of a building or a spider-hold in a basement. They can still achieve the same results of observing a desired area or target from these locations. Planners have to account for this.
Cover and Concealment
Cover and concealment are arguably the most important consideration in choosing key terrain. At the most primal level of combat, since the age of shields and swords, protection has been a constant. In the modern age, bullets and missiles cannot be stopped by body armor alone. In a city fight, thousands of tons of concrete and steel becomes the best form of protection. However, not all buildings and structures are built equal, and some will provide infinitely more protection than others.
For starters, most modern skyscrapers aren’t safe against direct fire weapons systems. Glass exteriors and drywall can only provide limited concealment and will not stop a bullet. On top of that, glass shatters creating falling debris that can extend for several blocks from a single explosion. It leaves behind treacherous shards all over floors and stairs. Combat leaders must be able to make onsite judgements about the structural integrity. They have to determine its resiliency of a building before they divert forces to occupy it.
While this may seem an impossible task, firefighters make these assessments every day in cities across America. Experienced FDNY firefighter William Carlson, a member of the National Center for Urban Operations Dense Urban and Subterranean Cell, explained to me exactly how the width of a fire escape on a New York City townhouse could show the number of apartments on the front side of a building, and how it could give away rear facing apartments and rear tenements, which would make ideal urban strongholds.
Leaders can identify load-bearing walls from indicators. They can identify the exact locations that, if destroyed, will collapse the entire building. Most junior officers and NCOs don’t know the intricacies of inner-city firefighting. But this example demonstrates that a visual sweep can provide an onsite analysis of an urban structure’s protective quality. Heavily reinforced concrete is very noticeably different looking from glass walls or weathered brick and mortar.
Key Terrain
Key terrain will be a deciding factor in urban combat. OAKOC is an extremely important tool and the standard reference to help leaders conceptualize terrain analysis in urban terrain.
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The effects of the different components of OAKOC do not exist in a void. While key terrain is just one factor, the other four combine to make a piece of terrain key. This is particularly true in a dense urban environment where the preset notions of key terrain are less clear. OAKOC provides an incomplete picture of the physical terrain of an urban battlefield. Still, leaders must use OAKOC to their advantage. This is chiefly true in determining and controlling key terrain that will enable the decisive operation of the mission. In so doing, leaders can mitigate risk to friendly forces.