The atomic bomb was developed because the Americans were scared that Hitler was researching to build one himself and win the war. That is also how the Americans joined the war.
The scientists were given permission to plan and build the project by president Roosevelt in 1942. They codenamed the project the Manhattan project and spent $2 billion overall on the project. More than 120,000 participated over the whole ordeal
The atomic bomb Little Boy weighed 4,400 kg (4tones) and was 3 meters in length and was filled with uranium. It was produced in 1945 and there were 32 built. The blast power is equivalent to 15 kilotons of TNT
The U.S wanted a city with a urban area of 4.3 km to study the effects of the bomb as well as wanting to end the war. The cities condemned were Hiroshima, Kokura, Niigata and Nagasaki. On the 6th of September the Americans were flying and the sky was clear over Hiroshima so it was dropped.
The explosion was the most devastating explosion ever. It emitted a heat Ray melting all steel and roof tiles within almost 2 kms from the hypocenter while anything dry within almost 2.5 km would immediately ignite. Every single thing within 500 m from the hypocenter was completely destroyed.
Black rain is a unnatural rain that occurred 30-40 minutes after the bombing. It comes from the mushroom cloud and goes black with dust and dirt but it is also radioactive. It will infect you if digested and will give you diseases and kill you.
Dear world leaders, I encourage you to look at the effects of the atomic bomb and think "should I have one of these or even threatening to use one" the effects consumed so many people and were devastating not just in size. So I say to all world leaders NO MORE NUCLEAR WEAPONS! You could hurt a lot of people lives or maybe start a world war by dropping one.