Little Boy: The First Atomic Bomb

August 6, 2020, marks the 75th anniversary of the dropping of the first atomic bomb. Today’s post comes from Michael J. Hancock, an archives technician at the National Archives at College Park, MD. 

Two American atomic bombs ended World War II in August 1945, and the devastation will be forever remembered. In an instant when the first bomb was dropped, tens of thousands of residents of Hiroshima, Japan were killed by “Little Boy,” the code name for the first atomic bomb used in warfare in world history. 

Hiroshima after atomic bombing, 1946. (National Archives Identifier 148728174)

The Project 

Scientists developed the technology for the atomic weapon during the highly classified project code-named “The Manhattan Project.” U.S. Army Col. Leslie R. Groves oversaw the military’s participation, while civilian scientist Robert Oppenheimer was in charge of the team designing the core details of Little Boy. Facilities for the research were set up in Manhattan, Washington State, Tennessee, and New Mexico. Scientists on the project drew from the earlier work done by physicists Enrico Fermi and Leo Szilard, both of whom received funding from the U.S. Government in the late 1930s to study enriched uranium in nuclear chain reactions. The enriched uranium-235 was the critical element in creating an explosive fission reaction in nuclear bombs.

The Manhattan Project team agreed on two distinct designs for the atomic bombs. In Little Boy, the first atomic weapon, the fission reaction occurred when two masses of uranium collided together using a gun-type device to form a critical mass that initiated the reaction. In effect, one slug of uranium hit another after firing through a smooth-bore gun barrel. The target was in the shape of a solid spike measuring seven inches long and four inches in diameter. The cylinder fit precisely over the spike as the two collided together creating the  highly explosive fission reaction. While the theory of the gun firing concept was not fully tested until the actual bomb dropped on Hiroshima, scientists conducted successful lab tests on a smaller scale that gave them confidence the method would be successful.

The final construction of Little Boy occurred in stages. Various components of the bomb were transported by train from Los Alamos, New Mexico, to San Francisco, California. There, the heavy cruiser USS Indianapolis shipped the collection of parts to Tinian Island in the Pacific Ocean south of Japan, where it arrived on July 26. In order to prevent a catastrophic accident, the target piece of enriched uranium flew separately aboard three C-54 Skymaster transport planes to Tinian Island, where it also arrived on July 26. Upon final assembly, Little Boy weighed 9,700 pounds and measured 10 feet in length and 28 inches in diameter. 

Once on Tinian, the officer in charge of Little Boy’s assembly, U.S. Navy Capt. William S. Parsons, decided to forestall the final segment of assembly until the very last moment. He did this in order to prevent a catastrophic accidental detonation caused by an electrical short or crash.

The Mission

In the early morning hours of August 6, 1945, a B-29 bomber named Enola Gay took off from Tinian and proceeded north by northwest toward Japan. The bomber’s primary target was the city of Hiroshima, located on the deltas of southwestern Honshu Island facing the Inland Sea. Hiroshima had a civilian population of almost 300,000 and was a critical military center that included 43,000 soldiers. 

Topographical map, Hiroshima. (National Archives Identifier 166126365)

The aircraft, piloted by the commander of the 509th Composite Group, Col. Paul Tibbets, flew at low altitude on automatic pilot before climbing to 31,000 feet as it closed in on the target area. At approximately 8:15 a.m. Hiroshima time, the Enola Gay released “Little Boy” over the city. Forty-three seconds later, a massive explosion lit the morning sky as the bomb detonated 1,900 feet above the city, directly over a parade field where soldiers of the Japanese Second Army were doing calisthenics. 

Even though the Enola Gay had already flown 11 and a half miles away from the target after dropping its payload, it was rocked by the blast. After the initial shock wave hit the plane, the crew looked back at Hiroshima, and Tibbets recalled that “The city was hidden by that awful cloud . . . boiling up, mushrooming, terrible and incredibly tall.”[1] The force of the explosion was later estimated at 15 kilotons (the equivalent of 15,000 tons of TNT).

Col. Paul W. Tibbets, Jr., pilot of the Enola Gay, waves from the cockpit before takeoff, August 6, 1945. (National Archives Identifier 535737)

The Legacy 

Many Americans viewed the bombing as a necessary means toward an end to the conflict with Japan. When Dr. J. Robert Oppenheimer was briefed on the bombing, he expressed guarded satisfaction. He, more than any other, understood  the power of the weapon he helped produce and the destruction that was unleashed on humanity. 

Enola Gay returns after strike at Hiroshima, 1945. (National Archives Identifier 76048622)

We will never definitively know how many died as a result of the bombing of Hiroshima.  Some 70,000 people are estimated to have perished as a result of the initial blast, heat, and radiation effects. This included about 20 American airmen who were held as prisoners in the city.  By the end of 1945, because of the continuing effects of radioactive fallout and other after effects, including radiation poisoning, the Hiroshima death toll was likely over 100,000.  The five-year death total may have even exceeded 200,000, as cancer and other long-term effects are considered.

Read the blog post Harry Truman and the Bomb and the notes of Captain Robert Lewis, co-pilot of the Enola Gay, to learn more about the first atomic aomb.


19 thoughts on “Little Boy: The First Atomic Bomb

  1. The Trunks of Hiroshina are still here…the. Last remaining relic…they carried the U-235 rings for the Bullet Assembly for the Gun…they rode on the USS Indianapolis to Tinian…no doubt the most valuable military relics of recorded history…see pics?…email me or Facebook….Thanks Little Boy…job well done!

    1. So far, I’ve heard nothing. For my Dad the massive attack resulted in an unconditional surrender and brought him Home, 7-1- 1945.
      Otherwise, if the bombs were not effective Dad’s unit from WW2, based in Spanhoe ,England… the 315 Airborne Group…34 Squadron would have been part of the Expeditionary Invasion of Japan. We stood to lose 500k Americans. Dad had been in theater 2 years and 7 months.
      His Unit dropped 800+ troops on D-Day behind the beaches of Omaha and Utah. @2:30 am… on St. Mere Elise.
      Hollwood made a movie out of it…”The Longest Dad”.
      I have fissile Cases the held for transferred Little Boy Parts and will sell them…Asking $6.M… these cases are rare since only 3 were fabricated…I have 2…there are no others…

  2. I believe the picture shown is not “Little Boy” but instead “Fat Man”, the second nuclear bomb which was dropped on Nagasaki.

  3. “I am become Death, destroyer of worlds.”

    JR Oppenheimer quoting
    sacred Hindu scripture at New Mexico
    test exploding first bomb

  4. I doubt that the “bombs” were assembled nLos Alamos as there was no train to haul them. The “Gadget” possible was hauled in two vehicles to White Sands and not through ABQ as rumored. So where?

  5. I’ve seen research stating Little Boy components were flown by C-47 from Kirtland AFB to Hamilton Field in Novato, CA then driven to Hunters Point Naval Shipyard to meet USS Indianapolis. Please respond with any information about Maj. Robert Furman who accompanied the shipment all the way to Tinian. Also seeking exact route shipment took from Hamilton to Hunters Point, thank you.

    1. My Father was a Captain involved with communications at Hamilton
      Field after serving for several years in the Pacific. He told me stories including the time he was told by the base commander that several
      planes would be landing for a short overnight stop over. The planes
      were off limits to the base personnel and were to be considered as a highly restricted area for their short stay. He told me that they were later told that it was connected to the transport of the first atomic


  6. I am glad we dropped this bomb, it probably ended the upcoming destruction of Japan in every sense. It saved me too; my Father was then preparing for the invasion of Japan in the Philippines. He was to be in the third wave going in to Honshu. Survival was a grim concept to entertain, for him, there was none, the bomb saved him, and the Japanese.

Leave a Reply

Your email address will not be published. Required fields are marked *