Obstructions, ropes and torpedoes
Through the summer of 1862 Charleston’s engineers worked on the harbor obstruction between Forts Sumter and Moultrie — piles, a rope entanglement to foul propellers, and the first of the torpedoes. When the ironclads came the following April, the obstruction was what turned them, without a shot being fired from it.
Official Records, Series I, Vol. 14