November 10, 1777. A cold, muddy island in the Delaware River, just south of Philadelphia. Inside the battered walls of Fort Mifflin, roughly four hundred American defenders waited for the sky to fall. They were hungry. They were sick. They were exhausted. The fort was unfinished, the ground was wet, and the British army already occupied Philadelphia. But the Delaware River still belonged, in part, to the Americans. Fort Mifflin, Fort Mercer, river obstructions, and a small A