Final answer:
The tune to Francis Scott Key's 'Defence of Fort M'Henry' is originally known as 'The Anacreontic Song'. It was later set to become the U.S. national anthem, 'The Star-Spangled Banner'.
Step-by-step explanation:
The tune to which Francis Scott Key's "Defence of Fort M'Henry" is sung was originally known as "The Anacreontic Song." Francis Scott Key wrote the poem during the War of 1812 after witnessing the American flag still flying over Fort McHenry despite the British bombardment. The poem was later set to the tune of "The Anacreontic Song" and eventually became the U.S. national anthem, "The Star-Spangled Banner."