<P> On Memorial Day, batteries on military installations fire a 21 - gun salute to the nation's fallen . As well, batteries at Naval stations and on ships, fire a salute of 21 - minute guns and display the ensign at half - mast from 8 a.m. until completion of the salute . </P> <P> Today, a 21 - gun salute is rendered on the arrival and departure of the President of the United States; it is fired in concordance with four ruffles and flourishes, which are immediately followed by "Hail to the Chief"--the actual gun salute begins with the first ruffle and flourish, and' run long' (i.e. the salute concludes after "Hail to the Chief" has ended). A 21 - gun salute is also rendered to former U.S. Presidents, foreign Heads of State (or members of a reigning royal family), as well as to Presidents - elect . In such a ceremony, the national anthem of the visiting dignitary's country is played, following the salute . </P> <P> In accordance with the ceremonial standard operating procedure (SOP) of the 3rd US Infantry (The Old Guard) the various gun salutes are assigned as follows: each round in a given salute is fired one at a time . The number of cannon used in a battery depends upon the intervals between each round fired . This includes, for example, a three - gun battery firing two of its guns with five - second intervals between rounds and one gun remaining at the ready in case of a misfire; such a battery would be used at an Armed Forces Full Honors Funeral, or for State Arrival Ceremony of a foreign dignitary at the Tomb of the Unknowns in Arlington National Cemetery . A four - gun battery has its first three guns firing rounds at three - second intervals, with the fourth gun (again) at the ready in case of misfire . </P> <P> The SOP also provides each gun salute a two - man gun crew (one loader, one gunner) for each cannon, as well as a five - man "staff" of soldiers to give the fire commands . The staff includes an Officer in Charge, a watchman (who marks the intervals and signals each gun to fire), an assistant watchman (as a backup), a counter (who keeps track of the number of rounds fired and signals the last round to the Officer in Charge), and a Non-Commissioned Officer in Charge (who marches the battery into place as well as signals the backup cannon to fire in case another gun misfires). </P>

Significance of the number 21 in the military