“The destruction goes beyond all description,” Ferdinand H. Gerdes of the U.S. Coast Survey wrote of the damage wrought by Union 13-inch sea mortars at Fort Jackson on the lower Mississippi in April 1862. “The ground is torn up by the shells as if a thousand antediluvian hogs had rooted it up. The holes are from 3 to 8 feet deep and are very close together, sometimes within a couple of feet. All that was wood in the fort is completely consumed by fire; the brickwork is knocked down, the arches stove, guns are dismounted, gun carriages broken and the whole presents a dreadful scene of destruction.”
The 13-inch Civil War sea mortar was a formidable weapon. But the use of this type of gun was not new; since the 17th century, high-trajectory mortar fire from special vessels known as bombs or bomb ketches had been used for shore bombardment. Heavy ordnance was more easily moved about on ships than on land, and the large sea mortars were mounted on strong beds turned on vertical pivots. Their explosive shells, fired at high angle, easily cleared the walls of forts to strike the targets within.