The U.S. has shown it can dominate on land, sea and in the sky, but its adversaries are going underground. The subterranean battlefield is a terrifying prospect, especially considering how unprepared the U.S. military appears to be to fight in that environment.

Due to the nature of subterranean warfare, engineers are responsible for finding a way into—and defeating—this growing threat. With the looming possibility of near-peer warfare and armed with the knowledge of underground tactics used in recent conflicts, the U.S. Army engineer branch should create a subbranch that confronts subterranean environments using unmanned systems and skills to neutralize these spaces.

With a specialized engineer subbranch in the main fighting force for combating subterranean battlefield environments, the Army would increase readiness. Soldiers trained in specific underground tactics using certain tools and robotics would decrease casualties caused by inexperience, and units could clear objectives without reallocating teams from the main mission.

Tough Tunnels

Hard and deeply buried targets are proliferating due to their effectiveness at evasion, and there is a silent arms race to create concrete that can withstand current bunker-buster bombs.

Over the past 30 years, scientists have been developing concrete that can withstand high explosives such as 5,000-pound bombs. The new and improved Ultra High Performance Concrete can withstand 40,000 pounds per square inch or higher due to the incorporation of steel or other fibers into the composition, according to a Sept. 19, 2022, online Popular Mechanics article headlined “The Covert Arms Race Between Bunker-Buster Bombs and High-Tech Concrete.” The fibers hold the concrete together and give it a higher fracturing rate.

So far, the U.S. Air Force has been able to keep up with these improvements in military-grade concrete, but just barely. In 2011, the Massive Ordnance Penetrator (MOP), manufactured by Boeing Co., was provided to the Air Force to be used on the deepest and toughest bunkers. The MOP weighs some 30,000 pounds and, due to its size, can only be delivered by a B-2 Spirit strategic bomber. Testing results were positive, but by 2018, the MOP had undergone four upgrades, according to the Popular Mechanics article.

The U.S. military has looked at harnessing hypersonic weapons to crack into these hard and deeply buried targets. Instead of packing explosives into a warhead, these missiles would rip through the atmosphere, hitting speeds higher than Mach 5, using only kinetic energy to punch through concrete.

Difficult Situations

DoD estimates there are 10,000 known or suspected hard and deeply buried targets across the globe. Of these targets, about 20% support a major strategic function in the area, and are in or near highly populated urban areas, according to the January 2021 book Strategic Latency Unleashed: The Role of Technology in a Revisionist Global Order and the Implications for Special Operations Forces, produced by the Department of Energy Lawrence Livermore National Laboratory’s Center for Global Security Research. These targets are used to protect an adversary’s leaders, conceal movements, store weapons and troops, and for countless other purposes.

The increasing frequency with which hard and deeply buried targets and underground facilities are utilized, especially when the civilian populace is added to the mix, creates difficult situations for leaders and soldiers tasked with eliminating those targets. “Although contemporary underground warfare remains primarily combatant-based, an extension to the civilian world is likely to further and sadly magnify the challenge. Groups such as the Islamic State, Hamas, and Hezbollah have demonstrated their willingness to place civilians in harm’s way,” according to the 2018 book Underground Warfare, by Daphné Richemond-Barak, an assistant professor in the Lauder School of Government, Diplomacy and Strategy at Interdisciplinary Center Herzliya, Israel, and an adjunct scholar at the Modern War Institute at West Point, New York.

Special operations forces and several small units within the U.S. military have been training in subterranean battlefield tactics for special missions against high-target bunkers and facilities. Multiple training centers across the U.S., including the Indiana National Guard’s Muscatatuck Urban Training Center, are cultivating new doctrines and operational concepts for subterranean battlefield warfare. As good as these teams are, more will be needed in future conflicts when battlefields are not in the woods or open desert, but within metropolitan areas. Therefore, specialized subterranean units within the Army would jump-start the military toward the future and prepare the U.S. for upcoming conflicts.

New Risks

This specialized subbranch within the engineer branch would need to incorporate not just sapper breaching techniques, but also chemical corps knowledge and robotics. Soldiers must be aware of changes inside tunnels. The enemy may expose soldiers to chemical and biological hazards that can’t be seen. Some examples include infectious diseases, decreased oxygen levels, carbon monoxide and smoke. Booby traps and blast injuries can damage the body, brain and hearing due to sound refraction in confined spaces. The list of new risks soldiers face increases the more elaborate the tunnels become. That is why robotics and unmanned systems should be incorporated.

Subterranean battlefield units could use robotics to test for chemical substances and changes in the environment, detect IEDs and map tunnels. Robotics could assist in carrying equipment such as air supply, breaching tools and casualties.

The 20th Engineer Brigade in July hosted the Sandhills Future Breaching Experiment at Fort Liberty, North Carolina. This experiment demonstrated how robotics and unmanned systems can be incorporated to reduce and validate complex obstacles.

Some of the systems showcased were ground-penetrating radar, the Small Multipurpose Equipment Transport, unmanned aircraft systems and algorithmic detection. Even though this equipment is used above ground, the technology can be incorporated into new and specialized systems specific to subterranean battlefield operations. The benefits of these systems would significantly decrease casualties and create more effective teams.

Technology, tactics and battlefields change constantly, and engineers must adapt to the shifting tides of war. A subterranean battlefield subset within the engineer branch would prepare the military for current and future operational challenges seen when facing adversaries with facilities and passageways almost untouchable by aerial weaponry.

Developing soldiers who combine breaching techniques, close-quarter combat and knowledge of chemical hazards and robotic systems will change how subterranean battlefields are mitigated and neutralized.

* * *

Capt. Amanda Cook, an engineer officer, is an operations officer with the 5th Engineer Battalion, 5th Security Force Assistance Brigade, Joint Base Lewis-McChord, Washington. Previously, she served with the 130th Engineer Brigade, Schofield Barracks, Hawaii. She is pursuing a master’s in geological engineering at Missouri University of Science and Technology.