On Monday, August 6, 1945, at 8:15 a.m., the
Atomic Bomb "Little Boy" was dropped on Hiroshima by an American B-29 bomber, the Enola Gay, flown by Paul Tibbets, directly killing an estimated 80,000 people. By the end of the year, injury and radiation brought total casualties to 90,000–140,000. The population before the bombing was around 340,000 to 350,000. Approximately 69% of the city's buildings were completely destroyed, and another 79% severely damaged.
A now deceased friend of mine who served in the British Occupation Forces after the end of the war once showed me photo's of peoples shadows etched for eternity into the pavement and sides of buildings from these bombings, lets hope we never see the likes of this again.
However stating it as a war crime is dubious when you consider that the Japanese were responsible for around 20-30 million civilian deaths during WW2.