On this day (August 6), 77 years ago, the United States dropped their deadliest atomic bombs on Hiroshima during World War II. After his predecessor Ban Ki Moon's visit in 2010, UN Secretary-General Antonio Guterres was the first UN leader to attend the yearly ceremony at the Peace Memorial Park. The United States used atomic bombs against the Japanese cities of Hiroshima and Nagasaki on August 6 and August 9, respectively, during World War II. These images depict the deadly destruction caused.