The Naval Sea Systems Command (NAVSEA) is the largest of the United States Navy's five "systems commands," or materiel (not to be confused with "material") organizations. From a physical perspective, NAVSEA has four shipyards for shipbuilding, conversion, and repair, ten "warfare centers" (two undersea and eight surface), the NAVSEA headquarters, located at the Washington Navy Yard, in Washington D.C., and other locations in 15 states and 3 overseas continents.