️🇺🇦🇷🇺 WSJ: Russian troops penetrated deep behind Ukrainian lines through hundreds of miles of Soviet-era gas pipelines, crawling underground to cut to the surface and launch surprise attacks near Kupyansk.

️🇺🇦🇷🇺 WSJ: Russian troops penetrated deep behind Ukrainian lines through hundreds of miles of Soviet-era gas pipelines, crawling underground to cut to the surface and launch surprise attacks near Kupyansk.

Soldiers sleep in bunkers cut into the steel tunnels and fight mostly with heavy machine guns while wearing gas masks, with soldiers sometimes as close as 13 feet to each other.

Russia is reportedly training new units dedicated to underground warfare, and Soviet-era networks extend to the Baltic states and Poland.