Johnston Atoll lies 1150 km (714 miles) southwest of Hawaii. The atoll consists of a coral reef, two highly modified natural islands, Johnston and Sand, and two completely man-made islands, Akau (North) and Hikina (East). The islands, which were used by the USA for nuclear weapons tests, were seriously contaminated with plutonium in 1962, when a nuclear missile exploded during testing. Regular tests began in 1971, and until 2000 the islands were also used for the storage of nuclear material and the destruction of chemical and biological weapons, including sarin nerve gas and the defoliant Agent Orange. Cleanup operations began in 2000. The only inhabitants left are US government personnel and civilian contractors who maintain the plant. The islands have also been designated by the USA as a wildlife refuge, a breeding place for seabirds and green turtles. The US army intends to evacuate the base entirely by 2003.