The 28th Infantry Division ("Keystone") is a unit of the Army National Guard and is the oldest division-sized unit in the armed forces of the United States. The division was officially established in 1879 and was later redesignated as the 28th Division in 1917, after the entry of America into the First World War. It continues its service today as part of the Pennsylvania Army National Guard. The 28th is also one of the most decorated infantry divisions in the United States Army.