The Tomb of the Unknown Soldier in Arlington National Cemetery is guarded year-round, 24 hours a day by Sentinels of The Old Guard. The guard is changed in an impressive ceremony at the tomb every half hour April through Sept. 30. During the winter months, the guard is changed hourly.

The Tomb Sentinel crosses the 63-foot walkway in a special measured cadence of exactly 21 steps. The Sentinel faces the tomb for 21 seconds before retracing his steps. The number 21 corresponds to the highest salute accorded to dignitaries in military and state ceremonies. As a gesture against intrusion on his post, the weapon is always carried on the shoulder farthest from the tomb.

Only under exceptional circumstances may the Tomb Guard speak or alter this silent measured tour of duty. Since 1948, the Tomb Guards have never left their post. The Sentinels take pride in maintaining a constant vigil as a way to honor those who have made the ultimate sacrifice in defense of their country.