Halo 2 did not have any disarm. It used sticky arming and certain map's arming circle varied depending on the map size or bomb arming location. You armed it, planted it in the middle, and round was over. Halo 3 took all of it away and went to instant arming, had a defuse, and took away other strategic HUD elements that made Assault great before. Reach was in the middle between the two by using an arm rather than instant, but it did have a diffuse setting. Neither Halo 3 or Reach went back to the objective return markers or sticky arming, for whatever reason!