League Island

League Island was an island in the Delaware River, part of the city of Philadelphia, just upstream from the mouth of the Schuylkill River, which was the site of the Philadelphia shipyard, which eventually became the Philadelphia Naval Shipyard, now known as The Navy Yard.

1891 USGS Topographic Map showing League Island at the confluence of the Schuylkill and Delaware Rivers

League Island no longer exists as an island, since the Back Channel, which separated it from the mainland, was closed at the eastern end to create land for Mustin Field, a military airfield that was closed in 1963. The western end of the channel became the present Reserve Basin, which holds the ships of the U.S. Navy's reserve fleet.