What exactly were the “rockets” mentioned in the U.S. national anthem?

The British were pounding Fort McHenry with a weapon that had been used against them twenty years earlier while they were conquering India in the 1790s.

Indian gunpowder experts had enlisted in the fight against British imperialism, pounding the British troops with a hail of primitive exploding rockets.

Though India eventually lost, the devastating effect their rocket barrages had on British soldiers caught the interest of an artillery expert, Colonel William Congreve.

Congreve’s rockets were inaccurate (people hadn’t yet figured out how to use stabilizing fins and vanes), and they exploded when the fuse fire reached them, not on impact. The result was that a number of rockets went off in midair.

So, like the Chinese and Indians before them, the British made up for the low quality of their rockets by increasing the quantity. Which makes sense, since “bombs bursting in air” have a terrifying effect, even if they don’t land exactly where they’ve been aimed.

From his vantage point as a prisoner on a British warship, Francis Scott Key likely saw thousands of these rockets launched against Fort McHenry.

No wonder he was so worried he had to write a song.