The bomb struck the center of the city, where some 250,000 people lived and some 40,000 military personnel were stationed. An estimated 80,000 people died in the explosion, which had the force of 12,000 tons of TNT and destroyed almost all of Hiroshima's buildings.
By December that year, another 60,000 Hiroshima residents had died due to sickness from the nuclear fallout. And over the following decades, thousands more died of cancer attributed to radiation exposure.
Three days after the bombing of Hiroshima, U.S. forces dropped another atomic bomb on the port of Nagasaki, where about half as many died as in Hiroshima. Almost immediately after that -- on 15 August 1945 -- Japan unconditionally surrendered.
The news of Japan's surrender was greeted in U.S. cities by huge crowds of people in spontaneous street celebrations. A radio announcer looking at the scene in downtown New York described it this way: "People -- I should estimate at least 350,000 or more, it's pretty hard to estimate at this point -- are cheering and screaming, making noise with sound makers, throwing confetti and bits of paper, streamers and all sort of things that they can find to celebrate this greatest of all victories, the surrender of the Japanese."
Today, 59 years later, Washington's decision to drop atomic bombs on Hiroshima and Nagasaki remains controversial.
Critics say that Washington should have opted instead for demonstrating the power of its atomic bomb in an uninhabited region. They argue that such a demonstration -- which would have saved tens of thousands of lives -- might have persuaded Tokyo that continuing the war was futile.
But those who defend bombing Hiroshima say there is no certainty a benign demonstration would have induced surrender and that Washington could not risk failure. They note Washington that had just two atomic bombs in its arsenal and counted on them to eliminate the need to invade Japan -- something that could cost the lives of hundreds of thousands of U.S. soldiers.
The debate may never be resolved because it largely rests on competing views of history. But the controversy is a measure of how strongly felt the emotions generated by the bombing remain decades later. Some of the strongest emotions are held in Japan, where the bombings of Hiroshima and Nagasaki have led to one of the world's strongest pacifist movements.
Christopher Hood is the director of the Japanese Studies Center at Cardiff University in Great Britain. He told RFE/RL that the bombings convinced many people in Japan that war in the nuclear age is too destructive to ever be justified. "The war [in the Pacific] was never a popular war and certainly by the time the war was turning against Japan, although the publicity machine would have said otherwise, at a popular level the Japanese people wanted the war to end," he said. "And so, when Hiroshima happened -- obviously initially they did not have any knowledge of what had gone on in Hiroshima but over the years the information came out and people could see the long-lasting effects of the war -- it really brought about this distaste for war itself."
Hood said the deep aversion to war is evident in the respect Japanese have for their explicitly pacifist constitution. Though the constitution was essentially written by the United States, which occupied Japan after the war, no major Japanese party has yet sought to change it.
"The Japanese have a pacifist constitution, the constitution itself renounces Japan's right to declare war, they are not meant to have any weapons at all. Now, as we know, in reality they have managed to get around this, so that initially they had a police force which became a self-defense force and the self-defense force is now actually being used abroad as in Iraq at the moment. But this idea of wanting peace, not wanting a repeat of Hiroshima is so embedded in Japanese society that it was a huge risk for [Prime Minister Junichiro] Koizumi to send the Japanese troops out to Iraq," Hood said.
In memory of the bombing of Hiroshima, tens of thousands of Japanese and people from other countries gathered today in the city's Peace Park. There they heard Hiroshima Mayor Tadatoshi Akiba criticize the United States for what he called its "egocentric" world view.
"The egocentric world view of the world is reaching extremes. Ignoring the United Nations and its foundation of international law, the U.S. has resumed research to make nuclear weapons smaller and more usable," Akiba said, and called for the world to dismantle its existing nuclear arms and ban all future production.