Short answers, pulled from the story.
British warships under Vice Admiral Alexander Cochrane bombarded Fort McHenry for 25 hours beginning at 6:00 a.m. on the 13th of September 1814. The fort held, and the British withdrew on the morning of September 14th after exhausting their ammunition, ending the Battle of Baltimore in an American victory.
Washington lawyer Francis Scott Key wrote the poem "Defence of Fort M'Henry" after witnessing the bombardment from a British truce ship. He saw an oversized garrison flag, sewn by Mary Pickersgill for $405.90, still flying over the fort at dawn on the 14th of September 1814, and was moved to compose what became the United States national anthem.
Fort McHenry was built between 1798 and 1800, replacing an earlier fortification called Fort Whetstone that had defended Baltimore since 1776. The Frenchman Jean Foncin designed the pentagonal bastion structure in 1798.
The fort was named after James McHenry (1753-1816), a Scots-Irish immigrant who served as a delegate to the Continental Congress from Maryland, signed the United States Constitution, and was United States Secretary of War from 1796 to 1800 under Presidents George Washington and John Adams.
Fort McHenry served as a military prison during the Civil War, holding Confederate soldiers and Maryland political figures who had criticized President Abraham Lincoln. Detainees included Baltimore Mayor George William Brown, the city council, police commissioner George P. Kane, members of the Maryland General Assembly, newspaper editors, and Francis Scott Key's grandson Francis Key Howard.
Fort McHenry was made a national park in 1925 and redesignated a "National Monument and Historic Shrine" on the 11th of August 1939, making it the only place in the United States to carry that dual designation. It was placed on the National Register of Historic Places on the 15th of October 1966.