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.

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The ground crew of the B-29 Enola Gay pose for a photo with the aircraft at their base in Tinian, Mariana Islands. Colonel Paul Tibbets, the pilot, is smoking a pipe in the centre of the groupUS Air Force/Reuters
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6 August 1945: Colonel Paul W Tibbets, Enola Gay's pilot, waves before take-offUS National Archives
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The atomic bomb, nicknamed Little Boy, is seen before being loaded into Enola Gay's bomb bayUS National Archives
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An atomic cloud mushrooms over Hiroshima, in this photo taken from the Enola Gay flying over Matsuyama, ShikokuNational Archives
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Aerial views of the city of Hiroshima before and after the atomic bomb was droppedNational Archives
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An aerial view of Hiroshima showing the devastation caused by a single atomic bombGetty
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6 August 1945: An aerial view of the damage at Hiroshima shortly after the atomic bomb was droppedKeystone/Getty Images
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6 August 1945: The remains of the barracks at the Japanese Army Divisional Grounds, about 1.3km from where the atomic bomb landed at HiroshimaKeystone/Getty Images
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6 August 1945: A building stands in ruins after the atomic bomb blast at HiroshimaKeystone/Getty Images
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A man wheels a bicycle through Hiroshima after the dropping of the atomic bomb. The street in this photograph is approximately half a mile from the location where the bomb was detonated, indicating the extent of the devastation to the city's buildings and roadsUS National Archives
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August 1945: The twisted wreckage of a theatre, located 800 metres from the epicentre of the atomic bomb explosionGetty
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A burnt-out fire engine is seen in the rubbleGetty

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.

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9 August 1945: Victims of the atomic bombing of Hiroshima are seen at an emergency relief station on the Otagawa River embankment in HiroshimaYotsugi Kawahara/Hiroshima Peace Memorial Museum/Reuters
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September 1945. The remains of the Prefectural Industry Promotion Building, which was later preserved as the Hiroshima Peace Memorial, Atomic Bomb Dome or Genbaku DomeAFP
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September 1945: A Japanese soldier walks through a flattened area of the cityNational Archives
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5 October 1945: Victims of the atomic blast sit in a makeshift hospital in a damaged bank building in the centre of HiroshimaKeystone/Getty Images
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October 1945: The skeleton of the Prefectural Industry Promotion Building, which was later preserved as the Hiroshima Peace Memorial, is seen through destroyed buildingsHiroshima Peace Memorial Museum
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A patient's skin is burned in a pattern corresponding to the dark portions of a kimono worn at the time of the explosionNational Archives
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November 1945: People walk past the Hiroshima Red Cross Hospital a couple of months after the atomic bombUS Army/Hiroshima Peace Memorial Museum/Reuters
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This colour photo of Hiroshima showing damage wrought by the atomic bomb was taken in March 1946, six months after the bomb was droppedReuters
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April 12, 1946: Crew members of the Enola Gay proudly parade through New York on a Jeep in the first Army Day Parade since the end of the warGetty
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1946: Wreckage of buildings in Hiroshima, a year after the dropping of the atomic bombKeystone/Getty Images
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August 1946: A view of Hiroshima one year after the atomic bomb. It was estimated that 6,000 to 10,000 corpses still lay under the rubble of the city that was 60% destroyed by the blastKeystone/Getty Images
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Circa 1947: A victim of the atomic bombing of Hiroshima shows the burns on his armsGetty
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Patients at the Tokyo Imperial University Hospital display injuries suffered as a result of the atomic bomb that was dropped on HiroshimaGetty
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1948: People look out over the devastated city of Hiroshima three years after the bombingAFP

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.

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29 March 1946: Bockscar, the plane that dropped the atomic bomb on Nakasaki, is seen in RoswellAFP
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Fat Boy, the atomic bomb that was dropped on Nagasaki on 9 August 1945US National Archives
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A mushroom cloud billows over Nagasaki after the atomic bomb was dropped on the city on 9 August 1945Reuters
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The radioactive plume from the bomb dropped on Nagasaki is seen from 9.6km away, in Koyagi-jimaNagasaki Atomic Bomb Museum/Getty Images
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Survivors walk through the shattered city of NagasakiUS National Archives
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Victims who were thrown clear of a tram are seen in a ditch near the the tracks, in NagasakiReuters
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Devastation is seen in the city of Nagasaki after the atomic bomb was droppedUS National Archives
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24 September 1945: Battered religious figures lie in the rubble of a destroyed temple on a hill above NagasakiUS National Archives

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.