Damage From Naval Bombardments
The largest naval guns used against land fortifications were fired on Fort McAllister in 1863 from monitor-type Union iron-clads. 15 in. shells penetrated 17 ft. of sand, digging craters 8 ft. in diameter and 7 ft. deep on exploding, but all damage could be repaired overnight.
Georgia Historical Commission 1964
Plaque courtesy Lat34North.com.
Original page, with additional info, here.
Photo credit: Byron Hooks of Lat34North.com.