On August 6, 1945, the United States dropped the first atomic bomb, making history as it killed thousands. Code-named “Little Boy,” the atomic bomb was used by the U.S. during World War II. Colonel Paul W. Tibbets was piloting the Boeing B-29 that transported the bomb.


Designing an Atomic Bomb


  1. Francis Birch was in charge of the design team that developed the nuclear weapon. Little Boy was classified as a gun-type nuclear weapon, one that depended on a single uranium-235 mass crashing into another one to cause a nuclear reaction. This means that the bomb’s core component was a smooth bore gun barrel. It was needed to fire the uranium projectile.


The bomb’s final design plans confirmed that Little Boy would use 64 kilograms of uranium-235. About 60 percent of it was formed into the bomb’s projectile, a cylinder featuring a 4-inch hole in the middle. The other 40 percent consisted of the target, and this was a solid spike that was 7 inches long with a 4-inch diameter.

“Little Boy” Atom bomb 3D Model

Once detonated, the firing mechanism would propel the projectile down the gun barrel using a tungsten carbide and steel plug, generating a critical uranium mass upon impact. The bomb’s tungsten carbide and steel tamper along with the neutron reflector were built to contain the mass.


At the time, there was a shortage of uranium-235. The lack of it prevented the bomb makers from conducting a full-scale test. Along with this, Birch’s team felt that they only needed to conduct small-scale laboratory tests to prove their concept due to the bomb’s simplistic design.


Ensuring Success


While the bomb’s blueprint essentially ensured that it would be successful, according to modern standards, its design is now considered rather unsafe. The reason for this is that several scenarios could have led to accidental detonation such as an electrical short circuit or a crash.


A Deadly Detonation


On July 14, 1945, several of the finished bomb units in addition to the uranium projectile were transported via train from Los Alamos to San Francisco. From there, the bomb components were moved to the USS Indianapolis, which shipped them to Tinian. The bomb parts arrived on July 26. Later that day, the military flew the uranium target to the island inside three C-54 Skymasters. With all of the pieces in one place, Little Boy was ready to be assembled.


Since handling the bomb was a dangerous endeavor, the man assigned to the task, Captain William S. Parsons, decided to wait to install the cordite bags into the bomb’s gun unit until it was in the air. After making the decision to use the nuclear weapon to fight Japan, military experts selected Hiroshima as the bomb’s target. Little Boy was loaded onto the Enola Gay, a B-29 Superfortress, which took off on August 6. The plane met up with two other B-29s over Iwo Jima. These planes were carrying instrumentation and photographic equipment.

WASHINGTON DC, USA – JUNE 21 2015: Boeing B-29 Superfortress Enola Gay at air museum . On 6 August 1945 the bomb, code-named “Little Boy”, was targeted by B-29 at the Hiroshima.

The Enola Gay made its way to Hiroshima where it let go of Little Boy over the city at 8:15 a.m. The bomb fell for 57 seconds until it detonated at 1,900 feet with a blast equaling that of around 13 to 15 kilotons of TNT. Little Boy killed 70,000 to 80,000 people and wounded an additional 70,000.


Retired from Service


Once the war ended, military higher-ups did not plan to use the inefficient Little Boy design again. Because of this, many of the bomb’s blueprints and diagrams were destroyed. However, the military wound up having to recreate them when the reactors at Hanford Site started showing signs of the Wigner effect, which is the displacement of atoms within a solid brought on by neutron radiation. This situation resulted in six Little Boy assemblies being built. In 1947, 25 more were put together. Toward the first of 1951, all Little Boy assemblies were retired from service.


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