SEOUL, South Korea — U.S. and South Korean troops honed their underground combat skills using drones and breaching tools as part of a recent large-scale joint military exercise across South Korea.

The drills serve as a signal to North Korea that its underground facilities are known to its adversaries and are under close watch. The South Korean Army's Ground Operations Command said Monday ...

Drones and quadrupedal robots could be used in the operation. South Korean and U.S. military forces have begun drills aimed at blocking and storming North Korea’s vast underground tunnel network, ...