Naval Base Subic Bay was a major ship-repair, supply, and rest and recreation facility of the Spanish Navy and subsequently the United States Navy located in Zambales, Philippines. The base was 262 square miles (680 km2), about the size of Singapore. The Navy Exchange had the largest volume of sales of any exchange in the world, and the Naval Supply Depot handled the largest volume of fuel oil of any navy facility in the world. The naval base was the largest overseas military installation of the United States Armed Forces, after Clark Air Base in Angeles City was closed in 1991. Following its closure in 1992, it was transformed into the Subic Bay Freeport Zone by the Philippine government.

Zambales, officially the Province of Zambales, is a province in the Philippines located in the Central Luzon region. Its capital is Iba, which is located in the middle of the province. Zambales borders Pangasinan to the north and northeast, Tarlac to the east, Pampanga to the southeast, Bataan to the south and the South China Sea to the west. With a total land area of 3,830.83 square kilometres (1,479.09 sq mi), Zambales is the second largest among the seven provinces of Central Luzon after Nueva Ecija. The province is noted for its mangoes, which are abundant from January to April.