Hiroshima Day 2020 is Observed to Mark the Atomic Bomb Attack on Hiroshima on August 6, 1945. On This Day, the United States Detonated a Nuclear Weapon Over the Japanese City of Hiroshima to End the World War-II. On Thursday, Hiroshima Day 2020 Marks the 75th Year of the US Dropping a Nuclear Bomb on Hiroshima in Japan.