A 32-pounder Seacoast Gun, mainstay of the United States' coastal defense in the mid-19th century. Fort James Jackson has two of these monsters, at least one of which was donated to the fort in 1999 by the Daughters of the Confederacy Savannah Chapter #2.

This gun is being supported by a block & tackle arrangement known as a casemate gin (although I've seen this contraption go by different names), which was the only way to manhandle impossibly hefty gun tubes onto their mounts.