U.S. Airmen with the 673rd Medical Group unload a simulated natural disaster casualty from an ambulatory bus for transport March 31, 2014, during an evacuation drill as part of a mission assurance exercise during Ardent Sentry 2014 at Joint Base Elmendorf-Richardson, Alaska. Ardent Sentry is a NORAD and U.S. Northern Command (USNORTHCOM)-directed exercise focusing on defense support of civil authorities in response to simulated weather, security and disaster contingencies. While Ardent Sentry is primarily a command post exercise, several field training events were conducted at various locations within the USNORTHCOM area of responsibility.