There were two amphibious assaults made upon Fort Fisher in Jan 1865. The second succeeded in part by the luck of the uncoordinated timing. The main assault was by sea, which drew all the attention of the Confederate defenders. But the secondary assault, which come from the back side of the fort via the Cape Fear River, was late, thus it found the sally port relatively undefended and broke through, which eventually led to the taking of the fort.
Here is a replica of the palisade near the sally port, looking onto the Cape Fear River: