U.S. Air Force Lt. Col. Shawn Campbell pins the Meritorious Service Medal on Senior Master Sgt. Sean Applegate, Air Combat Command food service superintendent, during his promotion ceremony to chief master sergeant at Langley Air Force Base, Va., May 31, 2012. Chief master sergeants, the highest enlisted rank, with the exception of the Chief Master Sergeant of the Air Force, serve as key leaders at all levels of the Air Force. (U.S. Air Force photo by Airman 1st Class Racheal Watson/Released)