The Philadelphia Naval Shipyard was an important naval shipyard of the United States for almost two centuries. Philadelphia's original navy yard, begun in 1776 on Front Street and Federal Street in what is now the Pennsport section of the city, was the first naval shipyard of the United States. It was replaced by a new, much larger yard developed around facilities begun in 1871 on League Island, at the confluence of the Delaware and Schuylkill rivers. The Navy Yard expansion stimulated the development over time of residential and businesses in South Philadelphia, where many shipyard workers lived. During World War II, some 40,000 workers operated on shifts around the clock to produce and repair ships at the yard for the war effort.