Barack Obama has become the first sitting US president to visit Hiroshima, site of the world's first atomic bombing. The two governments hope Obama's tour of Hiroshima will highlight a new level of reconciliation and closer ties between the former enemies.

At 8:15am on 6 August 1945, a 4,400kg nuclear bomb nicknamed Little Boy was dropped on Hiroshima by an American B-29 Superfortress bomber, the Enola Gay, flown by Colonel Paul Tibbets. The bomb was detonated 2,000ft above Hiroshima, releasing energy equivalent to around 15,000 tonnes of TNT, flattening five square miles (13 square kilometres) of the city in seconds. More than 60% of the city's buildings were completely destroyed.

An estimated 80,000 people died immediately, but injuries and radiation took the final death toll to around 140,000 from Hiroshima's population of 350,000.

Three days after the Hiroshima bombing, a larger atomic bomb was dropped on Nagasaki. The 4,500kg bomb, nicknamed Fat Man, was dropped from a plane called Bockscar. Estimates of the number of deaths vary from 39,000 to 80,000 people. Japan surrendered on 15 August 1945, bringing the Second World War to an end.

A majority of Americans see the bombings as having been necessary to end the war and save lives, although some historians question that view. Most Japanese believe they were unjustified.