On October 31, 1952, the United States successfully detonated the Los Alamos Mike thermonuclear device on the surface of Elugelab Island at Eniwetok Atoll in the Pacific Ocean. This test was the first demonstration of a high-yield thermonuclear explosion on Earth. The 10.4-Mt device yield obliterated Elugelab Island and left a 6240-ft-diameter underwater crater. Later, radiochemical analysis of the explosion debris produced the unanticipated discovery of 15 new heavy transuranic isotopes and two new elements, which were later named einsteinium and fermium. Initially, the discovery of these elements was classified, but in 1955, the results were declassified and announced to the world. The Mike results later led to the development of the Heavy Element and Isotope Effort under the U.S. Plowshare Peaceful Nuclear Explosions Program, under which additional new heavy transuranic isotopes were produced.