One of the oldest military bases in the United States— one that pre-dates the Declaration of Independence— Fort Mifflin, on the Delaware River in Philadelphia, Pennsylvania.
Commissioned in 1771, it was originally known as Fort Island Battery and, sometimes, as Mud Island since it sits on Mud Island. Renamed in 1795, the name honors continental Army officer and first post-independence Governor of Pennsylvania, Thomas Mifflin.
While the fort's military engagements date back to the American Revolutionary War, the Union utilized Fort Mifflin to house Confederate prisoners of war as well as Union soldiers and civilian prisoners during the Civil War. The fort served part of a Naval Ammunition Depot in World War I. In World War II, the Army also stationed anti-aircraft guns to defend the nearby Fort Mifflin Naval Ammunition Storage Depot and the Philadelphia Naval Shipyard.