Lt. Gen. Guy Swan III, commander of U.S. Army North,

Lt. Gen. Guy Swan III, commander of U.S. Army North, Adm. James A. Winnefeld, commander of U.S. Northern Command, and Brig. Gen. Clif Tooley, commander of Camp Atterbury and Muscatatuck Center for Complex Operations, answer questions during a press conference during the Vibrant Response 10.2 exercise at the Muscatatuck Urban Training Center in Butlerville, Ind., July 16. Vibrant Response is a national emergency response exercise involving more than 3,500 personnel participating in a scenario in which a nuclear weapon detonates in a major U.S. city.