U.S. Army UH-60 Black Hawks from the 7th Battalion, 158th Aviation Regiment sits on the parking ramp ready to take off at a moment's notice for a medical evacuation mission during Exercise Vibrant Response at Camp Atterbury, Ind., Aug. 22, 2011. Vibrant Response is the largest chemical, biological, radiological and nuclear response exercise designed to prepare expeditionary units focused on responding to domestic CBRN incidents.