The British fleet had weighed anchor at Cape Fear on May 31, and had arrived outside Charleston Harbor the next day.

Moultrie notices a British scout boat apparently looking for possible landing points on nearby Long Island (now known as the Isle of Palms), just a few hundred yards from Sullivan's Island; troops are consequently sent to occupy the northern end of Sullivan's.

By June 8, most of the British fleet have crossed the bar and anchored in Five Fathom Hole, an anchorage between the bar and the harbor entrance.

With the fort on Sullivan's Island only half complete, Admiral Parker expresses confidence that his warships will easily breach its walls.

Optimistically believing he will not even need Clinton's land forces, he writes to Clinton that after the fort's guns are knocked out, he will "land seamen and marines (which I have practiced for the purpose) under the guns" and that they can "keep possession till you send as many troops as you think proper".

The British fleet is composed of nine man-of-war ships: the flagship fifty-gun Bristol, as well as the fifty-gun Experiment and frigates Actaeon, Active, Solebay, Siren, Sphinx, Friendship and the bomb vessel Thunder, in total mounting nearly three hundred cannon.

The army forces in the expedition consist of the 15th, 28th, 33rd, 37th, 54th, and 57th Regiments of Foot, and part of the 46th.

On June 7, Clinton had issued a proclamation calling on the rebel colonists to lay down their arms.

However, the inexperienced defenders had fired on the boat sent to deliver it (which was flying a truce flag), and it is not delivered until the next day.

That same day, Clinton begins landing twenty-two hundred troops on Long Island.

The intent is that these troops will wade across the channel (now known as Breach Inlet) between Long and Sullivan's, which the British believe to be sufficiently shallow to do so, while the fleet bombards Fort Sullivan.

General Lee responds to the British landing with several actions.

He begins reinforcing positions on the mainland in case the British are intending to launch an attack directly on Charleston.

He also attempts to build a bridge of boats to provide an avenue of retreat for the fort's garrison, but this fails because there ware not enough boats to bridge the roughly one mile (one point six kilometers) channel separating the island from Charleston; the unwillingness of Moultrie and Rutledge to support the effort may also have played a role.

The Americans also construct an entrenchment at the northern end of Sullivan's Island, which is manned by more than seven hundred and fifty men and three small cannons, and begin to fortify a guard post at Haddrell's Point on the mainland opposite Fort Sullivan.