Timeline: The Road to Hiroshima

On August 6, 1945: the United States changed the face of warfare when it dropped an atomic bomb on Hiroshima, Japan. Three days later, U.S. forces detonated a second atomic bomb over Nagasaki, Japan, forcing an end to World War II. Here are the events leading up to that controversial attack.

December 1941: Japan bombs Pearl Harbor and the United States enters World War II.

1942: Physicist J. Robert Oppenheimer becomes director of the Manhattan Project, a U.S. government program formed to secretly build and test an atomic bomb. The project originally began to counter Nazi Germany.

May 7, 1945: Germany agrees to unconditional surrender, ending the war in Europe.

July 16, 1945: The United States successfully detonates the world's first atomic bomb at the Trinity test site in the desert of New Mexico.

August 6, 1945: The first atomic bomb to be used as a weapon is dropped on Hiroshima, Japan, at approximately 8:15 a.m. Nicknamed "Little Boy", the bomb is released from the Enola Gay, a B-29 bomber piloted by Brig. Gen. Paul Tibbets. It explodes 2,000 feet above ground, killing 80,000 people instantly. One of the main arguments for use of the bomb by U.S. officials is that it would force Japan to surrender unconditionally.

August 9, 1945: An atomic bomb is dropped over Nagasaki, Japan, by a B-29 bomber piloted by Maj. Charles Sweeney. It explodes 1,540 feet above the ground. The original target for the bomb, nicknamed "Fat Man", is Kokura, Japan. Due to cloud cover, the bomb is instead detonated over Nagasaki, the alternate location. It is estimated that 75,000 people are killed immediately.

August 9, 1945: Three days after the Hiroshima bombing, President Truman speaks to the nation in a radio address: 'My fellow Americans, the British, Chinese and United States governments have given the Japanese people adequate warning of what is in store for them. The world will note that the first atomic bomb was dropped on Hiroshima, a military base. If Japan does not surrender, bombs will have to be dropped on her war industries and unfortunately thousands of civilian lives will be lost. I urge Japanese civilians to leave industrial cities immediately and save themselves."

By this time, the United States had already dropped its second bomb on Nagasaki.

August 15, 1945: Japan surrenders, ending World War II.