If you haven't visited the Tomb yet I hope this video from the Arlington National Cemetery will put it on your bucket list. It describes the history and traditions associated with the selection of the unknowns, the cemetery and the Tomb Guards. If you have been or planning a trip I suggest reading Sacred Duty: A Soldier's Tour at Arlington National Cemetery by Senator Tom Cotton (R-AR) who served in the Old Guard at Arlington Cemetery. He describes the behind the scenes for all the ceremonies and parades done there and the life/duties of the soldiers. Just two points he makes in the book is the 'standing test' all in the Old Guard have to perform to qualify for duty there. To be able to stand at attention perfectly still in an observed test for quite some time as they would at a ceremony. Another is the bottom of the shoes for various functions are dyed black so that the troops don't 'flash' the spectators. Watch the Tomb Guards and you will see the soles are dyed black.