The Way Ahead is Down: The Case for Underground Defense
by Mark Thomas
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10.10.2025 at 06:00am
Introduction: A Role Reversal
To defeat China in armed conflict, the US military must embrace underground defenses. Military history repeatedly demonstrates that subterranean defenses are effective counters to superior firepower. The volcanic caves of Iwo Jima, the communist Vietnamese tunnels of Cu Chi, and the mountain hideouts in Afghanistan are all infamous in US military lore.
In each of these cases, American forces are always on the offense thanks to superior logistics, intelligence collection, and firepower. As such, current US military planners approach underground combat strictly from an attacker’s perspective, consistent with the American Way of War. There are specialized units, doctrine, and training to penetrate and clear underground facilities, but no reciprocal efforts dedicated to constructing and defending underground fortifications. There is an assumption that US forces will always be the side to force their adversaries underground. In the Pacific, this presumed position of strength is eroding daily as China expands its long-range strike capabilities. In response, the US military should invest in tactical underground defenses in the Pacific to harden allies, deter aggression, and hold key terrain in armed conflict.
The Limits of Dispersion
Any conflict with China in vicinity of the first island chain places the US at an extreme disadvantage. The People’s Liberation Army (PLA) enjoys shorter supply lines supporting an increasingly more sophisticated anti-access, area denial battle system. The PLA A2/AD system includes outposts of artificial islands, hundreds of maritime militia vessels, long-range missiles, fifth-generation fighters, and a growing navy built around modern aircraft carriers. This impressive constellation of sensors and shooters was developed to prevent the US from concentrating combat power, as demonstrated in the Gulf War.
To survive inside the PLA’s weapon engagement zone (WEZ), the US military is counting on dispersion. The Marine Corps divested heavier equipment, such as tanks and military bridges, in support of their Expeditionary Advanced Base Operations concept, which favors lighter, more mobile forces. The Air Force Agile Combat Employment concept eschews large, permanent air bases for smaller, temporary bases. The Army is creating mobile combat teams, trading their heavy joint light tactical vehicles (JLTVs) for lighter infantry squad vehicles built on a pick-up truck frame. These concepts are rational tactical solutions, but present serious vulnerabilities.
https://smallwarsjournal.com/2025/10/10/the-way-ahead-is-down-the-case-for-underground-defense/
