(WATCH) Battle Below

As Israel fights the Islamic extremist terrorist group Hamas, key aspects of the battle are taking place underneath the battlefield that most of us are familiar with. Lisa Fletcher reports on tunnel warfare and whether U.S. troops are prepared to face a like-positioned enemy.

As Israel’s army, the IDF, prepared to counter the Hamas terrorist attack of Oct. 7, they took 20 days to prepare the ground assault on Gaza, knowing that much of the fighting would be underground in a maze of booby-trapped tunnels.

Chris De Ruyter: Subterranean warfare essentially allows an enemy to defend and negate a stronger opponent’s capabilities. So by going underground, they’re able to take away combined arms maneuver and artillery and things like that.

Chris De Ruyter is a retired Army lieutenant colonel and former Ranger. One of the army’s elite. He’s worked with and trained the Israeli army in subterranean combat.

Lisa: As I’ve been watching the stories, and you see these seemingly limitless tunnels, it becomes obvious: these tunnels have been around for a really long time. It seems unlikely that IDF wouldn’t have known at some point they would end up there, right?

De Ruyter: Over a decade ago, the IDF recognized that these subterranean facilities existed, and someday they may be in a situation where they have to actually do something. So they actually started investing quite a bit into technology training and education, which is allowing them to actually conduct operations effectively today.

The Israeli military has shown video inside some of the tunnels it found, but just how extensive they are remains a mystery. Attackers can use tunnels to slip into enemy territory or undermine fortifications, as Hamas did. For defenders, tunnels allow for easier ambushes and counterattacks. They can also be used to hide and protect a nation’s most lethal weapons.

U.S. forces have faced underground threats in recent conflicts in Syria, Afghanistan, and Iraq.

Back in World War II, the Japanese made extensive use of tunnels on Pacific islands, most notably on Iwo Jima. In the Korean War, there was the Battle of the Twin Tunnels. And in Vietnam, American troops faced extensive tunnels booby-trapped by the communist guerilla enemy — the Viet Cong.

Lisa: So, does underground warfare negate the U.S.’s technological superiority?

De Ruyter: I wouldn’t say it negates it; it just makes the problem a lot harder. It makes operations, would have to be much slower, much more deliberate.

Col. De Ruyter was with the army’s Asymmetric Warfare Group. They were tasked with finding new ways to fight and deal with unconventional enemy tactics.

De Ruyter: When I was with Asymmetric Warfare Group, we would do some training with conventional units, and one of the very first things we did was put him in this dark area. It was designed to identify who has claustrophobia issues. There are some soldiers that are just not capable of operating in that kind of confined space once they got through the confined space trainer. So, even for the most seasoned warrior, it could be extremely unnerving.

Underground warfare isn’t part of regular training for most American soldiers and marines. There are more than 28,000 U.S. troops guarding the Demilitarized Zone between North and South Korea, many of whom do not have subterranean training. And there are at least four major known tunnel systems dug by the communist North.

De Ruyter: Take the North Korean regime — I mean, these are vast underground facilities that have everything that you can think of, from communication, to command centers, to living quarters and hospitals. So I mean, these are purpose-built underground facilities for combat and for military purposes. And I just mentioned that because it’s very different from some of the tunnels that we may be thinking about right now in this particular conflict in Gaza.

Lisa: I’m glad you mentioned that because I think the image that Americans have are these very rudimentary tunnels that are literally just tunnels dug through the ground — when you’re talking about entire cities laid out underground.

De Ruyter: Right, that are designed to withstand missile attacks, artillery attacks, and ballistic missile strikes. So they’re very purpose-built for survivability.

North Korea is just one of America’s enemies who have gone underground with large-scale tunnel systems. China has constructed subterranean missile sites and command centers. Iran’s underground nuclear facilities are well-documented, but the country has also exported its tunnel warfare expertise to terrorist groups like Hamas and Hezbollah. And Russia is using booby-trapped tunnels and trenches all along its front line with Ukraine.

Now, in the private sector, with an American research and consulting organization called the National Center for Urban Operations, De Ruyter believes the U.S. military should devote much more attention to subterranean warfare.

De Ruyter: It’s hard to train units up rapidly, because it takes time and resources to actually make them prepared to be able to go into this environment.

And maybe there might be something to learn from the enemy by taking some of our defenses underground.

De Ruyter: Our enemy has been using underground facilities for decades in order to help increase their survivability. It would make sense to start teaching our allies and partners how they can use underground warfare to their advantage from a defensive perspective.

In preparing to fight the battles of the future, it’s clear America will need to learn from Israel’s recent experience.

For Full Measure, I’m Lisa Fletcher in Washington.

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