The sentinels salute to the Tomb of the Unknown.

The Tomb of the Unknowns is the most symbolic site at Arlington Cemetery. The Tomb is guarded 24-hours a day, regardless of climatic conditions, by soldiers from the Army's U.S. 3rd Infantry, "The Old Guard." While guarding the Tomb, the sentinels take 21 steps before turning and facing the Tomb for 21 seconds. This corresponds to the 21-gun salute, America's highest military honor.

The Changing of the Guard ceremony is conducted each hour, on the hour, from October 1 to March 31, and every half hour from April 1 to September 30. At night the guard changes every hour.