It is believed that there were only two German U-boats that were able to enter the harbor. One occurrence was in September 1942, when U-455 was able to place a dozen mines at the entrance to the harbor. However, minesweepers detected the mines before they caused any damage. The flag pole inside the fort was broken and quite a bit of debris and mud was washed into the fort. Fortunately, no serious damage was done to the historic structures of Fort Moultrie.
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