U.S. Air Force Honor Guard ceremonial guardsmen perform a seven-man firing party during the final evaluations of training at Langley Air Force Base, Va., Feb. 29, 2016. The 21-gun salute has changed meanings and protocols several times since the 14th century, but today the 21-gun salute is meant to honor the death of a president in the United States. (U.S. Air Force photo by Airman 1st Class Derek Seifert/Released)