The mushroom cloud from the Ivy Mike nuclear test, one of two tests conducted as part of Operation Ivy at the Pacific Proving Grounds on Elugelab in the Marshall Islands. Mike was the first successful full-scale test of a multi-megaton thermonuclear weapon, and it left an underwater crater 6,240 ft (1,900 m) wide and 164 ft (50 m) deep where the island had been.Photo: United States Department of Energy