The Tomb of the Unknowns (also known as the Tomb of the Unknown Soldier) is guarded 24 hours a day, 365 days a year, by Tomb Guard sentinels. Sentinels, all volunteers, are considered to be the best of the elite 3rd US Infantry (The Old Guard), headquartered at Fort Myer, VA. The guard is changed every hour on the hour October 1 to March 31 in an elaborate ceremony. From April 1 to September 30, another change is added on the half hour. The Guards of Honor at the Tomb of the Unknowns are highly motivated and are proud to honor all American service members who are ''Known But to God''. This medallion is 2 1/4 inches in diameter.