The Fort Johnson flag was originally created for use as a signal flag by the merchant seamen of South Carolina. When the colonists began to discuss independence from the mother country, Great Britain, the ships serving South Carolina's naval interests chose this flag to represent their opposition to the British.
This flag was devised by Colonel William Moultrie in the Autumn of 1775 to be flown at Fort Johnson. On page 90 of his Memoirs, published in 1802, Moultrie (who had advanced from the rank of Colonel to Major General and later presided as Governor of South Carolina) stated: "A little time after we were in possession of Fort Johnson, it was thought necessary to have a flag for the purpose of signals: (as there was no national or state flag at that time) I was desired by the council of safety to have one made, upon which, as the state troops were clothed in blue, and the fort was garrisoned by the first and second regiments, who wore a silver cresent on the front of their caps; I had a large blue flag made with a cresent in the dexter corner, to be in uniform with the troops..."
In his memoir, Moultrie called the item that was worn in the caps a 'crescent'. It is very similar to the gorget that military officers of the time wore over their chests, just under their chins to protect their throats. The gorget (from the French gorge, meaning 'throat') had developed as a part of the armour worn by knights in the medieval period, and was an essential part protecting the throat. By the 1700s, though, with the gorget had become primarily an ornamental part of the military officer's uniform. The gorget was crescent shaped, and very well might have been the inspiration for Colonel Moultrie's use of it. It is known that the crescents worn on the caps of the First South Carolina Regiment, who partly garrisoned Fort Johnson, were engraved with the motto Ultima Ratio, and that William Cattell, commissioned as a captain in the First South Carolina Regiment owned a gorget that had the same motto engraved upon it. Whether Cattell's gorget was engraved with the motto after he became acquainted with the caps of the regiment's troops, on which the motto was engraved ~ or whether the regiment, becoming acquainted with the motto after Cattell appeared with his gorget, on which the motto was engraved, and had the crescents of their caps likewise engraved ~ has not been determined. One came first, but which is not known.
There are opponents to the idea that the crescent, as employed by Colonel Moultrie in his flag, might have been derived from the shape of the gorget. Those opponents suggest that it was an heraldic device. They tend to point to the Rutledge family, claiming that since the Rutledge family descended from an individual to whom an heraldic achievement had been presented (families, per se, were not granted coats of arms) in which a crescent was included, that that would have provided Colonel Moultrie with the design. The question arises as to why Moultrie would have used the ancestral heraldic device of just one particular prominent figure from the time, when there were other prominent figures from whom heraldic devices might have been obtained? Also, why would Moultrie not have mentioned that point in his description of the flag? If the Rutledge coat of arms was so important as to merit one of its devices being used for the flag, would it not have been mentioned?
Although Colonel Moultrie did not state that the crescent, as he designed it for the flag, was to be silver in color, the fact that he noted the caps bore silver crescents would imply that he utilized the same color on the flag. He noted that he designed the blue flag and crescent "to be in uniform with the troops", and therefore if the crescents in their caps were silver, it might be assumed that the crescent on his flag was likewise silver.
The design of the Fort Johnson Flag was unique among all the other flags of the time, and would remain so until the following Spring when the fort on Sullivan Island (Fort Moultrie) was erected and garrisoned.