Throughout history, the use of tunneling tactics has always been a common element of many guerrilla wars and asymmetrical conflicts. Like the National Liberation Front of Vietnam or the Mujahideen fighters of Afghanistan, the GLA also employed extensive tunnel networks in order to covertly move its fighters across considerable distances, smuggle supplies and provisions through even the tightest borders and strike swiftly from within the enemies own territory. Whereas the American response was to destroy the tunnels with deep-penetrating bombs, the Chinese initially doused the underground facilities with incendiaries, then sent their smallest soldiers into the tunnels to gather intel and demolish them. Many of these so-called 'tunnel rats' have told harrowing tales of burned out passageways littered with charred human remains and booby traps and despite the omnipresence of state propaganda, it stands as a tragic fact that many PLA veterans with such severe psychological trauma only receive a token amount of support from the Party government.
The Tunnel Network, available as soon as a Barracks has been built, can transport units across the map with ease. Inside the base, entrances like these aren't that necessary anymore, and they are built more around the battlefield, hidden by means of camouflage. This means that if enemies are moving nearby, a whole army can surprise them.