The ARC, short for Armored Response Coalition, is a global alliance of uncorrupted military forces, created by Samuel Hayden and using the best technologies of the UAC. They protect Earth's remaining population in well-defended safe zones, however despite their impressive firepower (including gigantic battle mechs), tactics and Hayden's use of the Crucible, they could never manage to turn the tide, only slow down the demon invasion a little; and their attempts at counter-attacks ended in disastrous failures, at least until the Slayer killed the Hell priests, destroyed the Super Gore Nest, and eventually destroyed the Icon of Sin.

The ARC broadcasts news of the player's progress at each return to the Fortress of Doom.