On June 28, 1776, 2,900 British regulars and marines launched an assault on the unfinished palmetto log and sand fort on Sullivan's Island from Long Island (known today as Isle of Palms).
The depth of Breach Inlet (separating the two islands) and its riptides were insurmountable obstacles to the British Army. Colonel William Moultrie's marksmen made an amphibious landing by British marines a failure. At the same time cannon balls from heavy British fleet fire bounced harmlessly off the spongy palmetto logs or embedded in the sand. During the fighting a shot severed the flagpole flying the South Carolina militia flag, This flag bore a white crescent moon in the upper left-hand corner on an indigo blue background (Indigo was a major crop in S.C.). Sgt. William Jasper attached the fallen flag to a gun sponger and remounted it on the fort.
At the end of the day the South Carolinians celebrated a glorious victory over the superior British force. Shortly after the Battle of Sullivan's Island, the white palmetto tree was added to the flag. Thereafter June 28th was celebrated as Palmetto Day with the same zeal as the 4th of July.
Excerpted from South Carolina: A History by Walter Edgar, 1998 University of South Carolina Press