Nuclear Engineering

How the Atomic Bomb Used On Hiroshima Works

How the mechanisms inside of Little Boy cost so many lives

By: Megan Lai, Journalist

May 29, 2025

Near the end of WWII, two atomic bombs were dropped on Hiroshima and Nagasaki on August 6 and 9, 1945 by the US. The two bombs were a representation of how much destruction humans could cause with the new idea of nuclear weapons. However, how were the two bombs used on Japan so powerful that they killed hundreds of thousands of people? For the purpose of explaining this, we will be talking about Little Boy.

The Components

Attached to the back of the atomic bomb are the box tail fins, which stabilize the bomb when it is dropped. Inside the bomb, near the end, there are the gun primers, which are responsible for launching the gun-like mechanism inside the bomb. In front of the gun primers is the cordite piece, which helps push the projectile at a really fast and explosive speed and force. Then, in front of that is the projectile tungsten disc, and finally, the uranium 235 projectile rings. These materials were ordered starting from the back and heading towards the front of the bomb. Now, we’ll start at the front of the bomb. At the front, there are uranium target rings, which is where the uranium rings from the back of the bomb will be pushed to, causing the nuclear fission. An important thing to note is that the uranium rings are hollow, so when the uranium rings hit the target rings, with a smaller diameter, fitting into the uranium 235 rings, the chain reactions with the nuclear fission begins. Outside the bomb, there are components that are added to the bomb to check the altitude of the bomb, so it knows when to start the chain reactions inside.

The Mechanism

Together, the gun primers and the other materials in between the back of the bomb and the uranium 235 rings launch a gun-like mechanism, pushing the uranium rings onto the uranium target rings. This starts a chain reaction, later causing nuclear fission. The nuclear fission happening in the bomb, in simple terms, is when there a neutron would split a uranium 235 neutron. The atom splitting would cause more neutrons to be released, causing more atoms to be split. As this happens, the amount of atoms inside increases at a rapid amount, which leads to an inevitable explosion, because the energy released from the chain reaction is really strong. At the right time and height, the bomb explodes, which is what actually happened on August 6. The bomb killed many people, using this mechanism, including nuclear fission and the splitting of atoms.