The army built this gun line, known as the South Battery, around 1840, while the present Fort Trumbull was under construction. By 1879, this battery contained eight cannon of two types, six Rodmans and two Parrotts. A low protective wall made of granite and earth, called a parapet, shielded the gun crews from enemy fire.
In 1879, four smaller siege guns stood on additional platforms in front of this gun line, on the edge of a cove that is now largely filled in. By 1892 they had been removed, and seven mortars had been installed in a line near the present parking lot. While the Rodmans and Parrotts fired cannonballs in a horizontal direction, aimed at the side of a ship, the mortars fired cannonballs up in a steep arc to fall on a ship from above. A magazine, a chamber for storing ammunition, was located on the west side of the line of mortars.
The South Battery, which was the gun position closest to Long Island Sound, held the largest concentration of heavy guns installed at Fort Trumbull in the 1890s.