Rockets and Bombs

The rocket's red glare, mentioned in "The Star Spangled Banner", resulted from the  explosion of 600 to 700 thirty-two pound Congreve incendiary rockets, fired at Fort McHenry by HMS Erebus. Due to withering American fire, the ship was forced to stay beyond the range of the fort's cannon. At that range, not many of the rockets reached their mark.

The bombs bursting in air were 13 inch and 10 inch explosive hollow iron balls, packed with gunpowder, weighing up to 200 pounds, fired by mortars. One bomb scored a direct hit on the powder magazine of Fort McHenry but failed to explode, saving the fort. During the 25 hour bombardment, between 1,200 and 1,800 rounds were fired on Fort McHenry by a British fleet of 19 ships.

Fort McHenry is a star fort, designed to withstand bombardment. Constructed with low walls, shielded by ditches to prevent direct fire reaching the walls, and walls topped by earthen fill to absorb the shock of descending missiles. Projections, called bastions, better position cannon to protect fort walls with crossfire, giving a star fort its star-like shape.