A soldier of the 3rd US Infantry, The Old Guard, watches over the Tomb of the Unknowns following a ceremony to observe the 235th birthday of the US Army at Arlington National Cemetery in Virginia on June 14, 2010. The Continental Army was formed on June 14, 1775, to fight the English during the Revolutionary War. The Old Guard is the oldest active-duty infantry unit in the Army, serving the US since 1784.