The Underground is a mysterious faction consisting of sewer-dwellers who live underneath Washington, D.C. Nothing is known of their history or their intentions, although they appear to be scavengers who come up to the surface to gather supplies. They are hostile to anybody they encounter. Unusually, Underground enemies have no voice lines whatsoever, and are only audible through their heavy footsteps.
Encounters with the Underground are infrequent and mostly randomized, although they are most commonly found in D.C.'s sewer system. They make a scripted appearance in the side missions Beekeeper Jeff, and Navy Hill Transmission.
Visually, the Underground are identifiable by their all-black clothing and the bright yellow flashlights worn around their heads. The Underground Tank wears heavy armor made from large chains.
Underground units are armed with basic weaponry limited to semi-automatic rifles, shotguns, and knives. Their Throwers use special grenades that apply chemical damage to their victims. Their Tanks are armed with chainsaws and behave similarly to the Outcast Tank.
Basic infantry unit armed with semi-automatic rifles. They have no unique abilities.
“ They mostly come out night... mostly. No, but seriously, they really do mostly come out at night. Hide your kidneys. ”
Agile units armed with knives. They can throw their knives from a distance or rush their target with melee attacks.
“ We've had a real problem with some of these guys just popping around corners and knifing some of our residents. Really vicious, unprovoked actions. I don't really condone killing people, but I won't shed any tears for them. ”
Special units armed with chemical grenades that apply effect damage to their targets. They are armed with pump-action shotguns.
“ Analysis of the toxic gas these guys use has mostly inconclusive, but whatever it is, I don't really our masks are up to the challenge of filtering it out. Maybe don't get caught up in it? ”
Armored unit equipped with rudimentary armor and a chainsaw. Tanks have no ranged weapons and can only use melee attacks; their chainsaws can apply the bleeding effect to their targets.
“ Medieval motherfuckers. See, this is why our decision to live above the ground floor was such a good idea. Nobody wants to be beaten with a flail. ”