Ascension Island is an isolated island of volcanic origin in the South Atlantic Ocean, around 1,600 kilometres (994 mi) from the coast of Africa, and 2,250 kilometres (1,398 mi) from the coast of South America. It is a dependency of the British overseas territory of Saint Helena, which is 1,287 kilometres (800 mi) to the south east. The Island is named after the day of its recorded discovery, Ascension Day. The island is the location of Wideawake Airfield, which is a joint facility of the Royal Air Force and the United States Air Force. The island was used extensively by the British military during the Falklands War. Ascension Island hosts one of five ground antennae (others are on Kwajalein, Diego Garcia, Colorado Springs and Hawaii) that assist in the operation of the Global Positioning System (GPS) navigational system. Ascension Island does not have its own flag or coat of arms. The Union Flag and Royal coat of arms of the United Kingdom are used instead.