Army 21 is an online action-strategy team combat game featuring base warfare, with co-op and versus game modes. Up to 60 players in 6 teams compete to defeat the other teams by building and defending their own base, and by destroying the bases of the opposing teams. Each base consists of a number of buildings of different types, each serving a unique purpose. When your team is defeated (when your base is destroyed) it is assimilated by the surviving teams.