On this day in 1814, the United States army forces at Fort McHenry in Baltimore, Maryland successfully defended the city from the British during the War of 1812. British warships bombarded the fort for over 24 hours, but the American defense held fast and by the morning of September 14th the British were forced to retreat due to lack of ammunition. The event, particularly the sight of an American flag being raised over the fort at dawn in celebration of victory, inspired Francis Scott Key to write a poem called ‘The Star-Spangled Banner’. Key was a witness to the battle because he was aboard a British ship having been trying to negotiate the release of an American prisoner. The poem was eventually set to the tune of a well-known 18th century British song and the anthem soon became a popular patriotic American song, and was commonly used by the armed forces. On March 3rd 1931, at the urging of many patriotic organisations, a congressional resolution was signed by President Hoover which affirmed 'The Star-Spangled Banner' as America’s official national anthem.