History

On December 7, 1941, Japan attacked Pearl Harbor. This was a surprise attack on the United States Pacific Fleet in Pearl Harbor, Hawaii. As a result, 21 American ships were sunk or damaged, 188 airplanes were destroyed, 2,403 people were killed, and 1,178 were wounded. The day after the attack, December 8, 1941, Franklin D. Roosevelt felt the immediate need to declare war on Japan.
After four years of war, the United States felt that they were ready to go to any extremes to end the war. During the time of the war the Office of Scientific Research and Development and the War Department were working together to build nuclear weapons for the United States. This program which was codenamed "The Manhattan Project", began to take place before the war even started. As their research and development came to an end, the Manhattan Project tested their first plutonium bomb on July 16, 1945 at the Trinity test sit in Alamogordo, New Mexico. With this success the United States were now ready to forgo their attack on Japan. 
Japan was not going to surrender, they had planned to fight until the bitter end. On August 6, 1945 at 8:15 am, the first 9,000-pound uranium-235 bomb called "Little Boy" was dropped 2,000 feet above Hiroshima and caused a blast equal to 12-15,000 tons of TNT. It destroyed five square miles of the city. Japan still would not surrender. Three days later on August 9, 1945 a second bomb that weighed nearly 10,000 pounds and was built to produce a 22-kiloton blast, was dropped on Nagasaki at 11:02 am. Because of the topography of this city, the destruction was reduced to 2.6 square miles. On August 15, 1945 at 12:00 pm, Emperor Hirohito announced Japan's surrender over a radio broadcast. 

This was the atomic bomb, "Little Boy", that was dropped on Hiroshima, Japan.

This was the atomic bomb, "Fat Man", that was dropped on Nagasaki, Japan.