 The land assault was frustrated when the channel between the two islands was found to be too deep to wade , and the American defenses prevented an amphibious landing . The naval bombardment had little effect due to the sandy soil and the spongy nature of the fort 's palmetto log construction . Careful fire by the defenders wrought significant damage on the British fleet , which withdrew after an entire day 's bombardment . The British withdrew their expedition force to New York , and did not return to South Carolina until 1780 . 
