Sergeant Jonathan Gleeson, a chemical, biological, radiological, nuclear defense specialist with 1st Marine Division, takes a photo of components a terrorist might use to make poisonous gas to harm civilians during a training exercise conducted during Urban Shield 2014 in the San Francisco Bay Area, Calif. Urban Shield is a four-day event that brings together local, regional and federal law enforcement agencies to include U.S. military service members as well as detachments from allied nations to share tactics and best practices in crisis response.