Enewetak, Enewetok, or Eniwetok (ĕnĭwēˈtŏk, ĕnēˈwĕtôk) [key], circular atoll, central Pacific, one of the Ralik Chain in the Marshall Islands. Enewetak is c.50 mi (80 km) in circumference and comprises about 40 islets surrounding a large lagoon. Mandated to Japan by the League of Nations in 1920, Enewetak was captured in World War II by U.S. forces. Designated an atomic proving station, it was the site of atomic tests from 1947 to 1962 (first thermonuclear tests). Former residents, evacuated before the tests started, began returning in the early 1970s, and the island was declared to have been rendered safe in 1980.