Background of an atomic bomb that was dropped in Hiroshima (Little Boy)
At first, America was planning to perform “Operation Downfall”, to assault Japan. However, after wtinessing the horror of Iojima and Okinawa battles, America changed the plan and decided to drop atomic bombs on Japanese soil. There were some opinions that they need to strike further with napalm or other type of weapons to maximize the damage, but the government decided against it. Before they dropped atomic bombs, nobody knew about the secondary damage caused by atomic bombs - radiation.
Little Boy, codename of an atomic bomb, was built with Uranium-235. Simply, Little boy detonates when 2 uranium masses colide, creating a massive heat and energy.
August 6th, 1945, 3 American planes flew above Hiroshima in order to recon the area. The citizens evacuated hastily, but nothing happened. After a few hours later, B-29 appeared on Hiroshima’s sky. The citizens thought it would be another recon plane, and continued their normal life.
But, the B-29 dropped an atomic bomb; It was 240 meter far away from Aioi bridge. Hiroshima citizens saw a very brightening light when it was detonated; some of the people were even blinded. Everything instantly burnt near the hypocenter at 3000~4000C. Soon, thermal effect and shockwave followed at 340 meter per second speed, wiping out everything on the ground (1.5 km radius). Hiroshima suffered from high radiation, heat and gray atmosphere preventing the sunlight sifting on Hiroshima’s soil.