Southern ports were blockaded by the U. S. Navy. One of my ancestors was a blockade runner, although I have been unable to find out how successful he was.
She looked like a veritable phantom ship of tradition as she glided past. No ghost could have moved more silently, or looked more mysterious; and we all felt a sort of mystical enchantment as we watched her rapid, stealthy progress. She was painted a smoky gray color, and could scarcely be distinguished in the light mist which enveloped her. Not a lamp gleamed aboard; no sound could be heard, except very faint echos from her revolving wheels,and no smoke seemed to be thrown out by her engines. Everything to ensure a successful trip had been carefully studied and prearranged. She passed like a spirit through the midst of the blockading squadron, and twenty-four hours later dropped anchor in the sparkling tropical waters of Nassau.
Apparently a lot of blockade runners got through. A visiting British colonel noted in 1863 that they were seldom captured.