The tomb guards are soldiers of the United States Army. The first military guards were troopers from the 3rd Cavalry, "Brave Rifles", who were posted nearby on Fort Myer. Since April 6, 1948, (known then as "Army Day"), when the regiment was reactivated, it has been guarded by soldiers from 3rd Infantry Regiment, "The Old Guard". The Old Guard is also posted to Fort Myer, Virginia, adjacent to Arlington National Cemetery. It is considered one of the highest honors to serve as a Sentinel at the Tomb of the Unknowns. Fewer than 20 percent of all volunteers are accepted for training and of those only a fraction pass training to become full-fledged Tomb Guards. This attrition rate has made the Tomb of the Unknown Soldier Guard Identification Badge the second least-awarded qualification badge of the United States military (the first being the Astronaut Badge).
The soldier "walking the mat" does not wear rank insignia, so as not to outrank the Unknowns, whatever their ranks may have been. Non-commissioned officers (usually the Relief Commander and Assistant Relief Commanders), do wear insignia of their rank when changing the guard only. They have a separate uniform (without rank) that is worn when they actually guard the Unknowns or are "posted".
The duties of the sentinels are not purely ceremonial. The sentinels will confront people who cross the barriers at the tomb or who are disrespectful or loud.