Little Boy, the atomic bomb thrown on Nagasaki, shortly before being loaded on the airplane.
In the years after 1895, people studying physics begin to understand how atoms are made. Around 1915, people began to have the idea that breaking special atoms can release large quantities of energy and can be used to make a bomb.
In 1939, people studying physics began to understand the theory of nuclear fission weapons, but no country knew how to build one. When World War II started, Germany, the United Kingdom and the United States wanted to build nuclear weapons. Germany did not finish building them, partly because many of the best people studying physics fled Germany after Nazi rule started. The United Kingdom started working in 1939, but it took too much money, so they gave up in 1942. Later that year, the United States started a very large program to build nuclear weapons. It built upon the work done in the United Kingdom. The program was called the "Manhattan Project".
By August 1945, the Manhattan Project built three nuclear fission weapons. Two of these bombs were used by the United States to attack the cities of Hiroshima and Nagasaki in Japan. People from the Manhattan Project believe that around 105,000 people were killed and 94,000 were hurt when the bombs were used. Medical professionals later came to believe that more than 225,000 people died when everyone affected after long periods of time are counted. Japan announced its surrender after the atomic bombings of Hiroshima and Nagasaki.
After World War II, the Soviet Union also began working to create nuclear weapons.
British Nuclear Tests Veterans Association memorial in Leicester