Fort Mifflin

Sitting on Mud Island, sometimes called Deep Water Island, along the Delaware River just south of Philadelphia and near what is now Philadelphia International Airport, this stronghold first entered service in 1771 under the name Fort Island Battery. Locals also knew it as Mud Island Fort.

When British forces set out to seize Philadelphia in the fall of 1777, they turned their guns on this outpost, shelling it into submission as part of that broader campaign. Nearly two decades later, in 1795, officials chose to honor Thomas Mifflin by giving the site his name; Mifflin had served as a Continental Army officer before becoming Pennsylvania's first governor following independence.

Reconstruction efforts began under the U.S. Army in 1794, and troops continued to occupy and expand the installation well into the following century. The site later served a grim purpose during the Civil War, when it held prisoners within its walls. Active duty for infantry and artillery units finally ended there in 1962, when the Army decommissioned the post.

Although the City of Philadelphia now holds the older section of the grounds, the U.S. Army Corps of Engineers still makes use of part of the property, a fact that gives this installation the distinction of being the oldest fort still serving the American military. Preservationists dedicated to historic sites have since restored the structure, and it now carries the designation of National Historic Landmark.

Decommissioning and restoration

Ownership of Fort Mifflin passed from the federal government to the City of Philadelphia in 1962. Seven years later, architect John Dickey took charge of bringing the Blacksmith Shop's bellows and forge back to working order.

The Army Corps of Engineers continues to operate out of Fort Mifflin, which holds the distinction of being the oldest active military installation in the country and the sole one still in service that existed before the Declaration of Independence was signed.

Fire claimed the Commandant's House sometime in the late 1970s, sparked by Boy Scouts who were camping at the site.

A more sweeping restoration effort unfolded during the 1980s and into the early part of the following decade, led by Harold Finigan, who served as the fort's executive director, alongside architects John Dickey and John Milner. Their work brought back the artillery shed, the hospital, the mess hall, officers' quarters, kitchen wings, the arsenal, and the soldiers' barracks, along with the north and west sally ports and the seawall. They also added a new bridge spanning the moat near the main gate. This project revealed that during the Civil War era, the buildings' exteriors had been coated in a yellow wash.

Wayne Irby brought to light what would become known as Casemate #11 when he excavated it in 2006. That August, Dr. Don Johnson led a handful of volunteers in exploring the casemate further, revealing an intricate network of inner rooms along with numerous historical artifacts hidden within.

Standing buildings

The site still preserves a collection of structures from its military days: an arsenal, an artillery shed, and a blacksmith shop stand alongside a sutler building that doubled as a storehouse. Also remaining are the soldiers' barracks, the officers quarters, and the commandant's house. A hospital that also served as a messhall can be found there too, along with the west sallyport and a series of casemates, including casemate number 11 and the east magazine.