Artillery

During the Revolutionary War, the armaments at Fort Mifflin were typical of those used at colonial forts. Cannons, the largest weapons, were obtained from France or captured from the British because of limited materials in America. These iron, smoothbore guns were classified by the weight of the round shot they fired, which ranged from 2 to 32 pounds. Mounted on wooden split carriages, field artillery used large wooden wheels banded with iron, and a 32-pound cannon measured over 9 feet long, had a 6.5-inch caliber, weighed 7,000 pounds, could fire a shot 2,900 yards, and required up to fifteen men to load, aim, and fire. Seacoast or garrison artillery was permanently mounted on carriages with small iron wheels designed to recoil back along rails for reloading, and all seacoast cannon were at least 18-pound guns. After Fort Mifflin's defeat, the British reported finding 14 field guns and 15 seacoast cannon there. American artillery production expanded after the Revolution, and in 1794 the new republic's First Defense System led to the fort's reconstruction, with ten 32-pound, eighteen 24-pound, and one 18-pound cannon mounted en barbette on the ramparts and eight 18-pound guns placed on the water battery below. These guns remained in service through the Second Defense System and the War of 1812. In 1836, the Third Permanent Defense system armed the fort with thirty 32-pound cannon, twenty 24-pound cannon, and nine guns on the water battery, while parapet walls were raised with treated timber for new platforms. During the Civil War, the fort was not manned for artillery defense, as the garrison mainly guarded prisoners in the casemates, though preparations began for target guns and the parapet walls were rebuilt in brick and slate. After the Civil War, the fort was refitted for more advanced weapons: in 1885, the old 32-pound and 24-pound guns and carriages were removed for scrap, and five Rodman cannon and fifteen rifled and banded 42-pound guns were installed. The Rodman was among the largest smoothbore guns ever fired, made possible by a casting method that hardened iron from the inside out and allowed the gun to withstand the force of 40 pounds of gunpowder. After 1850, rifling became the most important improvement in artillery, using a spiral groove in the bore to spin elongated projectiles and increase range, accuracy, and impact. The 42-pound and Rodman guns stood on iron carriages fixed to and rotating around front or center pintle stones, and the platforms and pintles for these guns remain visible on the ramparts.

Philadelphia, Pennsylvania · United States