Apr. 25, 1962 - The U.S. resumed nuclear testing in the atmosphere today by setting off an intermediate-size explosion near Christmas Island in the Pacific. The explosion took place at about 10:45 a.m. EST. Rising through the overcast skies, the mushroom-shaped cloud symbolized a new competitive phase in the atomic arms race and the frustration of more than three years of effort to reach an international agreement to prohibit atomic testing. It was the first atmospheric explosion by the U.S. since Oct. 30, 1958, just before a voluntary moratorium went into effect. The moratorium ended abruptly last Sept. 1, when the Soviet Union resumed atmospheric testing, a step that led to today’s long-debated action by the U.S.