American planners looking at contending with North Korea, ISIS remnants and copycats, and fighting in megacities against near-peer enemies have identified a shortfall of current U.S. training and focus: our enemies are turning to tunnels more and more, but modern U.S. forces have no idea how to best fight there.


An Army infantryman is lowered into Vietnamese tunnels during a search-and-destroy mission in Vietnam, 1967.

(U.S. Army photo by Staff Sgt. Howard C. Breedlove)

This has triggered a look at new technology and old tactics that could make the difference in fighting underground. The Defense Intelligence Agency has even floated the idea of a new warfighting domain: subterranean.

First, to define the problem. Insurgent and terrorist cells — notably ISIS, but also many others — have turned to tunneling to hide their activities from the militaries sent to stop them. Some of this is to allow fighters and supplies to flow across the battlefield undetected and unchallenged, but some of it is to hide intelligence and weapons or to force security forces to move through dangerous tunnels during last-ditch fighting.

Meanwhile, North Korea has been tunneling for decades just like communist forces did in Vietnam. Their military assets, including ballistic missiles and warheads, have been stored and moved through tunnels for years, making it harder to ensure an aerial first strike gets them all in one go. Iran has entire missile factories underground.

An Iranian missile is fired during testing. Iran has built three underground missile factories. In a potential war with the country, expect that someone will have to secure all the subterranean sites.

(Tasnim News Agency)

Modern infrastructure is increasingly built underground, from cable networks and natural gas systems to, increasingly, power lines. This leaves both America and its enemies vulnerable to disruptions of modern water supplies, information sharing, and power supply of multiple types due to underground attacks.

But Americans haven't fought underground on a large scale since Vietnam, and even the exploits of the heroic tunnel rats pale in comparison to what would be required to take and hold underground territory, especially under the cities and megacities that the bulk of human population will live in within a few decades.

So, the military has turned to DARPA and to long-term planners to figure out how American warfighters will maintain an advantage.

DARPA announced a new grand challenge last year called the DARPA Subterranean Challenge. The agency opened two research tracks: one for teams that wanted to compete in a physical challenge and one for those who would compete in a virtual challenge.

No matter the course selected, teams have to develop systems that will give American forces and first responders an advantage in human-made tunnel systems, the urban underground (think subways), and natural cave networks. The final event won't happen until 2021, but the winner of the physical challenge will get $2 million while the virtual track winner will get $750,000.

Meanwhile, the Army has invested $572 million in training soldiers to fight in subterranean networks with a focus on the sewers and other networks constructed either under large cities or as standalone bases. A 2017 assessment estimated that there are 10,000 military facilities constructed partially or entirely underground. Almost 5,000 of them are in North Korea.

"We did recognize, in a megacity that has underground facilities -- sewers and subways and some of the things we would encounter ... we have to look at ourselves and say 'okay, how does our current set of equipment and our tactics stack up?'" Col. Townley Hedrick, commandant of the Infantry School at the Army's Maneuver Center of Excellence at Fort Benning, Georgia, told Military.com in an interview. "What are the aspects of megacities that we have paid the least attention to lately, and every megacity has got sewers and subways and stuff that you can encounter."

Marine Corps Lance Cpl. Daron Bush roleplays a simulated casualty at Camp Gonsalves, Okinawa, Japan, Feb. 16, 2018. Imagine having to get injured Marines through miles of caves to medevac within the golden hour.

(U.S. Marine Corps Lance Cpl. Jamin M. Powell)

The military has been asking for new tunnel hardware for years. A 2016 wishlist from the Combating Terrorism Technical Support Office asked for technology that would detect and possibly intrude into tunnels. In 2017, the Army got a new piece of equipment that allows them to map underground tunnels to an unknown extent from the surface.

Still, there's a lot to be done. Troops will need less cumbersome armor or will be forced to fight bare in cramped quarters. Batteries will need to be light and compact, but even then it will be impossible to carry enough power to use many of the modern gadgets soldiers are used to. Many current technologies, like most radios and GPS, are useless with a few feet of rock disrupting signals, so special guidance and comms are essential.

Even with new gadgets and tactics, subterranean fighting will be horrible. Cramped quarters limit maneuverability, favoring a defender that can set up an ambush against an attacker who doesn't have room to maneuver. Front-line medics will take on increased responsibility as it will be essentially impossible to evacuate patients from complex cave systems within the golden hour.

So, expect a call for modern tunnel rats within the next few years. But, good news for the infantrymen who will inevitably get this job: You'll be equipped with a lot more than just a pistol and flashlight, and you might even have enough room to walk upright.