4.5 Inch Blakely Rifle
Made by Fawcett, Preston and Company (Liverpool, England), this rifle and the others like it came through the blockade on the British steamship Fingall, November 12, 1861. It fired a projectile weighing 24 pounds and had an effective range of about three miles. This gun and the second gun on your right were part of the original Confederate armament of Fort Pulaski.
Plaque courtesy Lat34North.com.
Original page, with additional info, here.
Photo credit: Byron Hooks of Lat34North.com.