ELMENDORF AIR FORCE BASE, Alaska -- Crew Chiefs from Kadena Air Base, Japan, conduct pre-flight checks on F-15 Eagles at Elmendorf Air Force Base, Alaska, May 13, 2008. There are more than 30 F-15s participating the Northern Edge exercise. The F-15 is a tactical fighter designed to gain and maintain air superiority. (U.S. Air Force Photo by Airman 1st Class Jonathan Steffen)