The Philadelphia Naval Shipyard was the first Naval Shipyard in the Nation. In 1799, Congress authorized $522,678 in funds for the purchase of land to establish the Philadelphia Naval Shipyard. The shipyard was originally located in the Southwark region of Philadelphia. However, with the growth of the city, the shipyard was relocated to its present site along Langley Avenue. The yard originated on Front Street in Philadelphia, and became an official United States Navy site, in 1801. With the advent of ironclad warships the site became obsolete and new facilities were built on League Island at the confluence of the Delaware River and Schuykill River, in Philadelphia, Pennsylvania. The Navy Yard was located at League Island, Pennsylvania, along seven miles of historic waterfront. The shipyard occupies 904 acres, with the industrial area comprising 360 acres. These are 390 permanent, semi-permanent, and temporary buildings, accounting for more than seven million square feet of shop space. The shipyard has five graving dry docks, and 29,044 lineal feet of berthing space. The Navy Yard’s Master Plan offers a mix of uses, building upon the four million square feet of existing activity and the 6,000 employees already located on site. With up to 12 million square feet of capacity for historic renovations and build-to-suit opportunities for office, research, and development, light and heavy industrial, distribution, marina and recreational uses, the Navy Yard is the Philadelphia region’s largest and most dynamic business location and development opportunity. For many years, the workload at the shipyard consisted primarily of new construction and conversions of ships. However, during the late 1960s at the direction of Defense Secretary McNamara the Navy gradually phased out of the new construction business, outsourcing this work to the private sector. Subsequently, Philadelphia Naval Shipyard was assigned ship repair and overhaul work. Its areas of expertise evolved to include high-pressure steam turbine engines, electronics, and combat systems. Philadelphia Naval Shipyard was typically assigned those ships requiring extensive electronics and combat systems work. The shipyard also performed the CV Service Life Extension Program and new threat upgrades, and the rebuilding of the Navy's eight conventional aircraft carriers. The new threat upgrade is a sophisticated electronics package and major ship alteration that makes older cruisers and destroyers compatible with the newest Aegis class cruisers. It ceased operations on September 27, 1996.