The U.S. Army came into being on 14 June 1775. The U.S. Marine were established on 10 November 1775. The Navy was established on 13 October 1775.The Coast Guard was formed on 4 August 1790. The U.S. Air Force became a separate service on 18 September 1947.he Navy was established on 13 October 1775. The Coast Guard was formed on 4 August 1790. The U.S. Air Force became a separate service on 18 September 1947.