Here we see an image of the first permanent armed military guard walking his post at the Tomb of the Unknown Soldier, Arlington National Cemetery, 25 March 1926.
Per Arlington:
On March 24, 1926, Major General Fox Connor, the Army’s deputy chief of staff, sent a memorandum to the adjutant general, explaining: “The Secretary of War desires that orders be issued establishing an armed guard (rifle) at the tomb of the unknown soldier in Arlington Cemetery…. If practicable, orders should be issued by telephone this afternoon in order that the guard may begin tomorrow morning.” Per these orders, the first armed military guard began duty at the Tomb on the morning of March 25, 1926.
The initial day guard, a detail of troopers from 2nd Squadron, 3rd Cavalry (Brave Rifles) at nearby Ft. Meyer, was later expanded to a 24/7 post in 1937, then assumed by the 3rd U.S. Infantry (The Old Guard)– who continue to stand post today— in 1948. 2-3 CAV, which had been sent to D.C. after arriving back from Occupation duty in Germany in 1919, spent so much time assigned to public duties around the District during the interwar period that it was known during this time as the “President’s Own.”
A smartly turned out 2-3 trooper on guard at the Tomb. Note the spurs as the regiment was still mounted until 1940.
The Tomb itself was dedicated on Armistice Day (11 November) 1921, making it 100 this year. Arlington has a special program to honor this somber milestone.