General Lee responded to the British landing with several actions . He began reinforcing positions on the mainland in case the British were intending to launch an attack directly on Charleston . He also attempted to build a bridge of boats to provide an avenue of retreat for the fort 's garrison , but this failed because it were not enough boats to bridge the roughly one mile ( 1 @.@ 6 km ) 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 constructed an entrenchment at the northern end of Sullivan 's Island , which was manned by more than 750 men and three small cannons , and began to fortify a guard post at Haddrell 's Point on the mainland opposite Fort Sullivan .