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Analyzing an Underground Facility for Large-Scale Combat Operations.


When learning about underground facilites, the intelligence professional might ask, "How are we supposed to provide a maneuver commander with accurate and timely threat assessments of an underground facility during largescale combat operations?" Then there is the logical followon question: "And how is that intelligence professional expected to provide the same information about any one of an estmated 4,800 underground facilites with litle or no intelligence?"

This article shares the lessons learned from my intelligence section during a deployment to the Republic of Korea on a regionally aligned forces mission. While deployed, we conducted intelligence preparation of the battlefield and the military decision-making process for countering weapons of mass destruction during subterranean operations. We had to learn a new set of skills and study a new field of information not presented to us previously. Ultmately, we learned that the subterranean environment is unique and that acquiring a basic understanding of its uniqueness will allow intelligence professionals to add valuable information to the decision-making process and increase the survivability of our Soldiers.


The United Nations predicts that by 2030, urban areas are projected to house 60 per cent of people globally and one in every three people will live in cites with at least half a million inhabitants. (1) This prediction is one of many that have refocused U.S. Army efforts to lay the groundwork for future operations in densely populated urban areas. This multi-domain ground conflict will include surface, vertcal urban, and subterranean realms. The subterranean domain will encompass underground facilites, building substructures (basements and parking garages), civil works (subways, transportation tunnels, and sewers), and their supporting infrastructure systems. Like military and government underground facilites, substructures and civil works provide similar challenges to the intelligence professional, but in a larger volume.

A perfect scenario would allow the intelligence team to collect city works blueprints, diagrams, or maps of these subterranean structures to use during the planning phase. More than likely, this information will not be available, and the intelligence team must use any imagery and opensource information it can obtain to answer the intelligence gaps. In the urban environment, the unknown terrain features will always outweigh the known. An example of this is the Iraqi campaign to retake Mosul from the Islamic State of Iraq and Syria (ISIS) fighters in 2017. It became apparent that ISIS was using a network of tunnels to move undetected throughout the city, but it was not untl Iraqi forces began clearance operations that they discovered entre city blocks were connected by passages created in the building walls. This discovery enabled the development of tactics, techniques, and procedures that forces used for the remainder of the operation.

When conducting operations inside urban areas and megacites, the team must identify the cultural construction norms to assist in planning. Terrain and cultural practices will drive construction characteristcs for housing, subway systems, and underground civil works, and will establish a planning base. The team can then verify the assumptions developed during planning or can discard them as the operation develops. Understanding the terrain inside a megacity is challenging, and the subterranean domain is only a portion of this vast environment.

Understanding an Underground Facility's Purpose

Underground facilites are not a new addition to the modern battlefield. Soldiers and civilians have used tunnels and underground terrain before--in World Wars I and II, the Korean War, the Vietnam War, and the War on Terrorism. Technological advances have expanded the complexites of these underground facilites, thus creating a more challenging environment for friendly operations. To resolve this problem, the intelligence professional cannot always wait for the different intelligence enttes to answer information requirements and fll intelligence gaps. The intelligence professional must draw conclusions with limited information and deduce what makes sense in order to assist the unit's operations process. To fulfill the intelligence warfighting requirements for subterranean operations, it is important to understand the purpose of the underground facility, assess the environment that friendly forces will encounter inside the facility, and effectively map the facility for current and follow-on operations. These tools do not only relate to the Korean theater of operations; the underground facility remains a point of contention in Army studies and refinement efforts in identflying the best approach to the multi-domain megacity challenge.

Understanding an underground facility's purpose is the largest piece of the puzzle, and it will provide the most relevant information to the ground force commander. ATP 3-21.51, Subterranean Operations, describes this environment and its characteristcs. To understand the subterranean world, analysts first need to comprehend the surface terrain features and their signifcance to the associated underground facility. Dynamic pieces of the puzzle include roadways, areas cleared of vegetation, footpaths, power lines, ventlation shafs, sewer pipes, portal locations, and civilian infrastructure. If roadways are present leading into the underground facility, then the corridors inside will be wider than facilites with a footpath entrance, reducing the risk of overpressure (2) injuries and increasing maneuverability.

Assessing the Underground Facility and Creating the Visual Product

Depicting the known location of portals (3) on a topographic map creates a relatve size comparison for the facility, which can assist in determining its maximum occupant capacity and relationship to one another. The locations of these portals also assist in determining if the underground facility is multlevel based on differences in elevation. The facilites' umbilicals (4) will also be identfable on the surface level. Underground facilites of greater importance will be more sophistcated and will contain internal and external life-support systems. Evaluating these systems will aid in determining the amount of time a facility is able to remain closed of from the outside environment. Selectvely removing any of these critical systems provides courses of action to the ground force commander for ofensive approaches to deprive the threat and improve the probability for a successful tactical callout.

The type and level of a facility can be determined using these tools and readily available intelligence such as basic imagery. Hardened artllery sites, weapons depots, batle positions, contnuity of operations bunkers, and factories are just a few types that are of a different construction, with a variety of defensive measures and barrier levels. Diferent barrier levels require different breaching assets and time allocations for a successful breach to occur.

Afer assessing an underground facility's purpose, create a visual product showing the assessed underground facility's layout. This product will become the tool for the ground force commander to plan all aspects of the surface and subterranean operation; therefore, it needs to be comprehensive. The product should depict portal locations and type, internal barrier classification (5) and evaluated breach times, internal wall construction, types of rooms located inside (aid station, command post, munition storage, etc.), defensive measures, and ultmately the threat's composition and disposition. The visual product's level of detail is time-dependent and can be digital, analog, or a combination of both. The best method to create this product is to begin with a blank piece of acetate laid onto a topographic map encompassing the underground facility's location.

To start, identify and mark the known portal locations to identify the size of the underground facility and its internal network. The ventlation shaf, observation posts, or other umbilicals will aid in the layout because their tes to the underground facility are more than likely associated with underground corridors or rooms. Afer depicting all the known information, remove the sketch from the map and fll in the remaining information gaps. Accomplish this by deducing what makes sense based on what is known and by using a practical approach to annotate the unknowns. An example is assuming that the command post is closer to the center of the underground facility, not close to the portals where it is more vulnerable. Afer all of the knowns and unknowns are illustrated, an analyst has a working product to refine and expand on. This is a critical process and is the base for all other warfighting functions and commanders to plan operations.

A Toxic Environment

The environment inside an underground facility is more lethal to our forces than the threat forces themselves. Add the potential for weapons of mass destruction, and it becomes the deadliest environment a Soldier will encounter. The air, lighting, structural integrity, overpressure risk, sound amplifcation, and threat forces play a role in this lethal environment and are all equally important to consider. Oxygen levels, explosive gasses from firearms, smoke, carbon monoxide, carbon dioxide, and chemical and biological agents will at a minimum reduce the stamina and effectiveness of our forces and have the potential to be fatal. That is operating on the assumption that a sufcient oxygen rato is present inside the underground facility to begin with and the use of oxygen tanks is not required. Chemical detectors and air quality sensors are the most effective way to detect these threats once inside, but the intelligence analysts must provide planning assessments prior to entry.

The threat and civilian protectve measures displayed on the objectve before arrival is a starting point to determine the environment of an underground facility; however, forces should take into account that less-developed countries may have different safety standards and regulations. At a minimum, though, forces that approach an assessed weapons of mass destruction site must wear mission-oriented protectve posture (MOPP) level four gear, with the appropriate detectors. When approaching a non-weapons of mass destruction site, forces should apply a deliberate tempo to avoid passing the point of no return before any symptoms take effect. The intelligence section owes the ground force commander an assessment of when to transition friendly forces into MOPP gear when countering weapons of mass destruction operations. Only when the environment demands it should Soldiers wear MOPP gear because it affects Soldiers' combat efectveness by reducing their stamina and overall situational awareness. The chemical officer's knowledge of the chemical, biological, radiological, and nuclear agents assessed to be on the objectve will assist the intelligence section in determining the various MOPP gear transition points and protection level upgrades for friendly forces as they approach the underground facility.

U.S. forces own the night, but not the dark. Night vision devices rely on ambient lighting to enhance images for the operator to see. Inside an underground facility, lighting systems may turn of at a moment's notce; before gaining entrance, operators need to plan how they will produce ambient lighting with infrared lasers, chemical lights, or visible lights, or use thermal imaging devices. A ground force commander may decide to use the lack of lighting as an ofensive measure if access to the power supply system is ready and if the team has assessed the threat to lack night vision capability.

Structural Integrity and Overpressure

Finally, it is critical to understand the structural integrity of the underground facility and overpressure potential. The structural integrity of the foors, walls, and ceiling directly corresponds to the level of facility assessment and correlates to the classification level of the portal barriers and overall facility importance. Higher barrier classifcation levels present at the portals indicate a more important facility, resulting in fnished and reinforced walls and ceilings in most instances. The internal construction methods affect overpressure and the efficiency with which it channels through space. The stronger the walls and ceiling within the underground facility, the more damage it can withstand from small arms and explosives, such as grenades, but this will also increase the ricochet effects of rounds and shrapnel, and will channel overpressure more directly.

Because a shockwave over atmospheric pressure causes overpressure, it can be lethal to humans and can result in severe disorientation similar to the effects of alcohol intoxication. Smaller spaces, larger explosions, and proximity to overpressure-producing sources will increase the effects of overpressure. This requires analysis so that the ground force commander can determine weapon employment and direct fire control measures inside the underground facility.

Mapping the Underground Facility

Mulitple levels, corridors, portals, rooms, and dead space result in an interweaving maze that could continue for kilometers with no end in sight. The templated layout derived from the overall purpose of the underground facility and environmental characteristcs will only provide a limited understanding and is primarily a planning tool. When the entry and clearance operation begins, it is imperative that a designated element be responsible for mapping the underground facility, and the element must consistently provide updates to the tactical operations center. Human intelligence reports from civilians or enemy prisoners of war near the objectve can be helpful to refine the understanding of the facility. If not, refinement will only commence aftrer ground forces or robots gain entrance to the underground facility. Refnement will remain an ongoing process that is critical to the overall success untl the operation is complete.

The best approach to mapping the underground facility is to display the templated layout next to a clean piece of acetate or on a whiteboard visible to all personnel inside the operations center. Having both products side by side will provide a visual product to batle track with, create a common operational picture, and refine the underground facility's layout simultaneously. Using one of these methods, begin mapping from the point of entry and continue based on reports from the clearing unit as the operation unfolds. The blank slate approach allows for easy modification of the templated layout. Human intelligence and lead unit reporting can improve the layout, which can also depict significant activites in time and space. If possible, the clearing team should constantly be searching the underground facility for diagrams or writing on walls to assist with the mapping process.

Ultmately, friendly forces will clear the underground facility and subsequently begin exploitation. The exploitation phase is when fnal mapping refinement is completed. Techniques include using a paceman or measuring wheel for distance and protractors or rudimentary angles for azimuth (because the underground environment may affect compass accuracy). If available, three-dimensional mapping cameras are useful to create a digital rendering of the facility. This is especially helpful for planning purposes if a higher unit's exploitation team is required at the objectve, such as the chemical response team or nuclear response team.


The underground facility is the worst imaginable environment in which friendly forces will conduct operations. The unknown facts surrounding underground facilites outweigh the known facts tenfold. Intelligence professionals owe the ground force commander accurate assessments of underground facilites even when intelligence is limited. Using only surface-level information collection products, an analyst is more than capable of assessing an underground facility's purpose. The analyst can provide information about the underground facility's environment and can produce accurate mapping updates of the underground facility hroughout the operation and untl completion of the exploitation phase. Most importantly, the intelligence analyst must provide recommendations to the ground force commander that allow the commander to identify, assume, and mitgate risks when planning and executing the clearance operation inside the underground facility. As intelligence professionals, we cannot fear assessing the unknown; we must do what we can for friendly forces to conduct successful operations within an underground facility.

The use of subterranean facilites will remain an afordable and effective means to defeat high tech information collection assets in the future. If the intelligence team focuses on each aspect of the subterranean environment, refines assumptions throughout the operation, and studies the cultural construction norms, the team can answer megacity intelligence gaps for the ground force commander.


(1.) United Nations, Department of Economic and Social Afairs, Population Division, The World's Cites in 2016 (2016), ii, htp://

(2.) Overpressure is the "pressure caused by a shock wave over and above atmospheric pressure." Department of the Army, Army Techniques Publication 3-21.51, Subterranean Operations (Washingtion, DC: U.S. Government Publishing Ofce, 21 February 2018), 3-30 (common access card login required).

(3.) A portal is the "structure surrounding the immediate entrance to a mine; the mouth of a cave or tunnel." Ibid., 1-15.

(4.) Umbilicals are the "supporting Infrastructure that allows a system to function." Ibid.

(5.) There are three barrier classification levels. "The classification of barriers is used to quickly identify and describe the materials used to build portals and entrances to subterranean spaces and structure." Ibid., 1-17.

by Captain Nicholas G. Pena

CPT Nicholas Pena commissioned into the U.S. Army as an infantry officer from the University of Central Florida Reserve Officers Training Corps program in 2012, graduating with a bachelor's degree in business management. He served as an infantry platoon leader and executive officer in the 2nd Battalion, 502nd Infantry Regiment, 2nd Brigade Combat Team, 101st Airborne Division, from 2012 to 2017 and deployed to Afghanistan in support of Operation Enduring Freedom. After attending the Military Intelligence Officer Transition Course and Military Intelligence Captains Career Course at Fort Huachuca, AZ, CPT Pena was assigned to the 2nd Battalion, 7th Infantry Regiment, 1st Armored Brigade Combat Team, 3rd Infantry Division, as a battalion intelligence officer, deploying as part of a regionally aligned force to the Republic of Korea in 2018.
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Author:Pena, Nicholas G.
Publication:Military Intelligence Professional Bulletin
Date:Jan 1, 2019
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