JERUSALEM ― The U.S. and Israel are continuing joint work to improve tunnel detection, specifically those used by militant organizations such as Hamas and the Islamic State group. The collaboration will continue through 2020, and this year’s budget is expected to reach similar levels as the $80 million the U.S. contributed in 2016-2017.

Tunnel warfare isn’t new, and the joint effort against the threat brings together experience that Israel and the U.S. have from current and previous conflicts. The U.S. confronted extensive tunnel systems in Vietnam. However, militant groups are increasingly resorting to tunnels as a way to avoid surveillance by drones and other aerial assets.

As technology improves, adversaries have sought to counter such innovation by digging deeper and more complex tunnel systems. In Iraq, for instance, ISIS honeycombed cities with tunnels whose exits were contained inside civilian homes, hidden from aerial view.

The U.S. Marine Corps trained with Israeli paratroopers in March on combating the tunnel threat, and research and development funding stands to benefit both countries in developing technology, such as acoustic-detection systems, that will aid in future battlefields and modern threats.

As part Juniper Cobra 2018 exercise in March, the Marines and the Israel Defense Forces participated in a variety of drills. The sub-exercise Kaya Green, for example, included training aimed at learning from Israel’s experience in tunnel warfare. This built on major strides Israel has made over the last decade in engineering, intelligence and use of technology to find and destroy tunnels.

For the fourth time in three months, Israel employed what is being called here its “steel dome” to detect and destroy a cross-border tunnel from the Gaza Strip.

“We did a joint training session with them, fighting side by side, with the armored vehicles, and the way they used them was really effective,” Lt. Ron Semel told the Times of Israel.

In the last six months, Israel has detected and destroyed several impressive tunnels constructed by Hamas. One of these tunnels sought to reach into Egypt and was struck in January. Israel has called its strategy of using technology and intelligence to combat the tunnel threat a “steel dome” in contrast to its Iron Dome system that confronts missiles.

In the first week of June, the IDF destroyed a tunnel in Gaza with an airstrike. Unlike most of the tunnels built by Hamas ― which are built to penetrate Israel or used for smuggling from Egypt ― this one was built underwater to allow Hamas seaborne commandos to move undetected at sea. It was almost 3 meters deep and only 3 kilometers from Israel’s border, an IDF spokesman said.

But the tunnel-detection systems Israel has been pioneering with U.S. support has wider implications.

Geographically speaking, U.S. lawmakers have pointed to North Korean subterranean tunnels as a reason to boost U.S.-Israel research and development efforts against this growing threat.

In March, 56 members of Congress wrote in a joint letter to the Committee on Appropriations‘ Defense Subcommittee that “our own nation faces similar threats [to those in Israel]. In Iraq, Afghanistan and Syria, ISIS has used subterranean passages to smuggle weapons, avoid detection, ambush troops and launch tunnel bomb attacks.”

For their part, Reps. Brad Schneider, D-Ill., and Dan Donovan, R-N.Y., have sought to pass the United States-Israel Anti-Tunnel Defense Cooperation Act to enshrine the tunnel cooperation in legislation.

In December, the United States’s fiscal 2018 National Defense Authorization Act included continued monetary support for the joint tunnel program. According to the legislation, 50 percent of that funding must be used for “research, development, test and evaluation activities in the U.S. in connection with such support” ― and the program was extended through 2020.

So far, more than $82.5 million was spent in 2016-2017 on the joint program, and similar figures are expected in the coming years. The anti-tunnel efforts build on previous successful collaborative efforts to counter missile threats that have seen Israel develop the Iron Dome, Arrow and David’s Sling systems.

But the tunnel-detection technology goes beyond purely military applications.

Elbit Systems reportedly wants to export some of the technology that it has helped develop as a partner in the program. The detection system could be used to combat tunnels used for smuggling drugs across the U.S.-Mexico border, among other areas. In April 2016, the U.S. uncovered a tunnel stretching half a mile from Mexico into San Diego, California. It was the largest of 13 uncovered since 2006.

There are also a network of tunnels left over in areas liberated from ISIS in Mosul, Iraq, and Raqqa, Syria. These continue to bedevil the return of civilians, who suffer casualties from improvised explosive devices and fear ISIS may be hiding out in elaborate tunnel systems that have not been fully explored or destroyed.

Seth J. Frantzman is the Israel correspondent for Defense News. He has covered conflict in the Mideast since 2010 for different publications. He has experience covering the international coalition against the Islamic State group in Iraq and Syria, and he is a co-founder and executive director of the Middle East Center for Reporting and Analysis.

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