Near Kupyansk, Ukrainian forces (ZSU) and the Russian military are reportedly fighting within Soviet-era pipelines, with distances between adversaries sometimes narrowing to 4 meters, according to The Wall Street Journal. Russian forces are using underground pipes to cover kilometers unnoticed, flanking ZSU positions and launching drones from there.

The Wall Street Journal reported that Russian forces are utilizing underground pipelines to advance undetected, reaching ZSU rear positions to launch drones. Ukrainian forces initially responded with artillery and air strikes against pipe exits, but Russian forces adapted by creating new openings, leading to direct underground combat. In these pipelines, approximately 1.2 meters in diameter, Russian forces have established fortified positions, including machine gun nests and living quarters.