Model of Hiroshima after the atomic bomb blast seen in the Hiroshima Peace Memorial in Hiroshima, Japan on August 5, 2009, one day prior to the 64th Hiroshima atomic bomb attack by the U.S. (the only nation to ever use nuclear weapons against human beings). Hiroshima citizens held activities and events to mark the anniversary. The U.S. detonated a massive nuclear bomb over the Japanese city at an altitude of some 600 meters at the end of WW II, killing an estimated 140,000 people at 8:15 a.m of Aug. 6, 1945 (Xinhua/Ren Zhenglai).