Foreign Policy: “For more than a decade, the United States has targeted insurgents from the sky with increasingly advanced drones, launching air strikes in Iraq, Afghanistan, Pakistan, Yemen and other volatile countries. But the practice may be contributing to a new trend: foreign militaries and insurgents are using tunnels and other underground networks more and more to hide and gain a tactical advantage — and that increases the likelihood that U.S. forces will face them below ground in the future.”

“The U.S. Army just issued a warning about tunnel warfare as part of a new effort seeking high-tech robotics, communications gear and other equipment. Army officials requested industry’s help on Thursday, saying ‘the growing use of tunnels and underground facilities by military and irregular forces to gain a tactical advantage is becoming more sophisticated and increasingly effective, making the likelihood of U.S Forces encountering military-purposed subterranean structures on future battlefields high.'”