Johnston is a coral atoll about 700 mi southwest of Hawaii. It consists of four small islands—Johnston Island, Sand Island, Hikina Island, and Akau Island—which lie on a 9-mile-long reef. The atoll was discovered by Capt. Charles James Johnston of HMS Cornwallis in 1807. In 1858 it was claimed by Hawaii, and it later became a U.S. possession. Johnston Atoll was used by the U.S. Air Force to conduct test launchings of nuclear missiles and contains a landfill of plutonium-contaminated waste. More than four million pounds of chemical weapons have been destroyed on Johnston since 1990, and the U.S. military has been fined several times since then for improperly handing VX and sarin gas and releasing the deadly substances on the atoll. The military is gradually departing and the atoll will be turned into a wildlife refuge. However, the U.S. Fish and Wildlife Service, the atoll's inheritor, is concerned about the possibility of eventual radioactive leakage.