WATCH: The crowds may be gone at Arlington National Cemetery this Memorial Day, but the Changing of the Guard still goes on. Sentinels from the 3rd U.S. Infantry Regiment, known as "The Old Guard,” stand watch over the Tomb of the Unknown soldier 24 hours a day, 365 days a year. The Changing of the Guard ceremony -- which happens every half hour during the spring and summer -- now includes more distancing between personnel, and soldiers now wear face masks in their quarters as they prepare for t