American forces on Port Royal Island consisted of a small detachment of the 4th South Carolina regiment (Captain John de Tréville commanding) and some militia. These men defended Fort Lyttleton, which protected the town of Beaufort, but which could not stop the British from landing and raiding elsewhere. On January 31, the militia abandoned the fort. Captain de Tréville then hastily spiked the guns and blew up the fort .
That night, Brigadier-General William Moultrie reached the ferry crossing to Port Royal Island and learned that the fort had been destroyed. A sizeable force of South Carolina militia encamped near the ferry, including men from the relatively well trained and equipped Charleston regiment. 
On February 2, Moultrie crossed over to Port Royal Island with close to 300 men, and the next morning he marched into Beaufort. There, Moultrie found that some arms and supplies could be salvaged from Fort Lyttleton, but before any action could be taken, word was received that the British were about 5 miles away. Moultrie then assembled the men and marched after them. 
The two forces met about halfway between Beaufort and the island ferry. At this point, the British were between the Americans and the ferry. At the same time, the Americans threatened to separate the British from their boats.
Captain Patrick Murray, who commanded a British light infantry company, claimed that the battle was fought “along the road to the entry of Rhodes’ Swamp, where—on the crest of the Pina Barren beyond the swamp where the trees were felled but not cleared off.” 
The Americans halted about 200 yards from the British. The Charleston Artillery deployed in the road, and the infantry were deployed in two wings that extended into the woods on either side. Captain de Tréville took with him a 2-pounder when he abandoned Fort Lyttleton; this gun was positioned in support of the right wing.
The British troops consisted of three light infantry companies supported by a small howitzer (manned by 2 gunners and 6 sailors). The infantry deployed in nine platoons, which from left to right (when facing the Americans), were commanded by Lieutenant Joseph Breitenbach (4th battalion, 60th regiment) Captain Patrick Murray (4/60th), Lieutenant Rowland Hosleton (4/60th), Ensign James Finlay (3rd battalion, 60th regiment), Captain George Bruère (3/60th), Ensign Enoch Plumer (3/60th), Lieutenant John Skinner (16th regiment), Major Colin Graham (16th), Lieutenant William Calderwood (16th). Each platoon contained around 16 men. 
1. The number of captured slaves is stated in a letter from Stephen Bull to William Moultrie, dated February 12, 1779. The quoted passage appears in a letter from Lieutenant Benjamin Smith to Moultrie. Moultrie’s correspondence appears in his memoirs (published 1802).
2. Moultrie noted that “Although the fort was blown up, yet it was not so totally demolished but that a great many of the stores were left unhurt, and the guns so lightly spiked, that you might draw out the spikes with a pair of pincers.”
3. Two companies of the Charleston regiment served in this battle: the 2nd company (Charleston Artillery, commanded by Captain Thomas Heyward) and the 3rd company (Charleston Light Infantry, commanded by Captain John Baddeley). Also present were other local militia, although I have not been able to divine their numbers or organization. Of these other men, Moultrie singled out a troop of light horse commanded by Captain John Barnwell. Brigadier-General Stephen Bull commanded the militia, and Lieutenant-Colonel Barnard Beekman commanded the artillery. Moultrie had overall command.
According to Moultrie, the only Continentals in this action were in Captain de Tréville’s detachment, which consisted of de Tréville, 2 junior officers, and 6 enlisted men.
Serving with the Charleston Artillery were two signers of the Declaration of Independence: Captains Thomas Heyward and Edward Rutledge.
Some relevant pension applications (links are to. pdf files):
- John Anthony of the Charleston Artillery. He was wounded during the battle and is named in Moultrie’s correspondence.
- Lieutenant Archibald Brown of the Charleston light infantry. He was wounded during the battle and is mentioned in Moultrie’s account.
- Lieutenant George Frederick Dener. He served in the Charleston light infantry.
- Jonathan Johnson. He served in the Charleston light infantry.
- Lieutenant Edward Barnwell. He was Captain John Barnwell’s brother and served in his troop.
- William Elliott. He served in Barnwell’s troop.
4. The number of men that fought in the battle may have been considerably less. Moultrie noted, “The Chehaw company was sent back before the action, about 125 men, on a report that the enemy had landed there.”
5. This quote appears in Peter Young’s (1967) The British Army, which describes the battle of Port Royal Island in considerable detail.
6. This order of battle is based on Young and this history of the 60th regiment.