Defence Alliance 2 is a total conversion mod for Killing Floor featuring team based futuristic FPS game play. DA2 blends fast paced action with class based tactics to create an experience that is instantly enjoyable while still offering very deep gameplay. Two teams face off in attack/defend scenarios where the attackers must complete their objectives before time runs out. The mod features six different classes: Medic, Mechanic, Rocketeer, Machine Gunner, Sniper and the Rifleman, each with their own special abilities. Players can set up their own turrets such as cannons, miniguns, and rocket turrets, place ammo boxes, heal other players, use EMP grenades and rocket launchers against turrets, and more.

In addition to the regular DA2 gameplay mode, Defence Alliance 2 for Killing Floor now features a new gameplay mod called Co-op Specimen Survival. A small group of players are set against waves of specimens. Players can use turrets and mines to build up their defense then have a limited amount of respawns with which to defeat the waves of incoming specimens.