On Aug. 6, 1945, the United States dropped an atomic bomb on the city of Hiroshima. On Aug. 9, 1945, a second bomb was dropped on Nagasaki. The bombings resulted in thousands of causalities in Japan. 

The decision to drop the bombs on the cities is controversial, even today, due to how many lives were lost. Thousands of people died from the atomic bomb, but the action also ended World War II. 

Here is everything you need to know about Hiroshima and the atomic bomb. 

A nuclear explosion in Hiroshima on August 6, 1945

The first of two atomic bombs dropped on Japan was in Hiroshima on Aug. 6, 1945. The second was dropped in Nagasaki three days later. (History/Universal Images Group via Getty Images)

5 THINGS TO KNOW ABOUT HIROSHIMA OTHER THAN THE ATOMIC BOMB 

  1. Why did the U.S. bomb Hiroshima?
  2. How many people died during the Hiroshima bombing?
  3. Who invented the atomic bomb?

1. Why did the U.S. bomb Hiroshima? 

The United States bombed Hiroshima during World War II. The bomb was dropped so that Japan would quickly surrender, and the war would end, instead of more lives being lost over the course of a continuing war. 

On Aug. 6, 1945, the first of two atomic bombs was dropped on Japan, in the city of Hiroshima. The 8,900-pound bomb, named "Little Boy," was dropped by The Enola Gay, a B-29 Superfortress plane. The second of the two bombs, called "Fat Man," was dropped three days later in Nagasaki. 

The atomic bombs did lead to the end of the war. President Harry Truman announced Japan's surrender on Aug. 14, 1945. 

FATHER OF THE BOMB: J. ROBERT OPPENHEIMER

The destruction from the atomic bomb in Hiroshima

Ninety percent of Hiroshima was destroyed due to the atomic bomb. (Universal History Archive/Universal Images Group via Getty Images)

2. How many people died during the Hiroshima bombing?

Thousands of people died during the Hiroshima bombing, both immediately and from radiation symptoms weeks later. 

Prior to the Hiroshima bombing, the population of the city was 350,000. Of those 350,000, 40,000 were military. 

The estimated death toll from the bombing is 140,000, which includes those who died due to radiation-related injuries and illness all the way through Dec. 31, 1945. Most people who died from radiation symptoms died three to six weeks after the bomb was dropped. 

The death toll to date from the Hiroshima bombing is 300,000. This number is so much higher because it includes those who have died from radiation-related cancers. 

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J. Robert Oppenheimer at his desk

J. Robert Oppenheimer is known as the "father of the atomic bomb." (PhotoQuest/Getty Images)

About 90% of the city was destroyed from the atomic bomb. 

3. Who invented the atomic bomb?

The atomic bomb was developed in a secret government initiative known as the Manhattan Project, which was led by theoretical physicist J. Robert Oppenheimer. More than 130,000 people were employed in the highly classified mission to create the first atomic bombs. 

The project had a budget of over $2 billion, and main development took place from 1942 to 1945. On July 16, 1945, the first nuclear explosion occurred in a test located near Los Alamos, New Mexico. The atomic bomb test was code named "Trinity" and was a success.