page_title: Little Boy
section_title: Rehearsals
hierarchical_section_title: Little Boy / Rehearsals
caption_attribution_description: English: Atombombe. LB (Little Boy) unit on trailer cradle in pit on Tinian island, before being loaded into Enola Gay's bomb bay. [Note bomb bay door in upper right-hand corner.] , 08/1945. ARC Identifier: 519394. Français&#160;: La bombe Little Boy sur son berceau sur l'île de Tinian, avant d'être chargée dans la soute de l'Enola Gay. La porte de la soute est visible dans l'angle supérieur droit de l'image. Deutsch: Die Atombombe Little Boy auf der Insel Tinian auf einem Sicherungsgestell kurz bevor sie in den Bombenschacht von Enola Gay Enola Gay geladen wird. [Bombenschachttür in der oberen rechten Ecke.] , 08/1945. ARC Identifier: 519394.
context_page_description: "Little Boy" was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II. It was the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress Enola Gay piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces and Captain Robert A. Lewis. It exploded with an energy of approximately 15 kilotons of TNT and caused widespread death and destruction throughout the city. The Hiroshima bombing was the second man-made nuclear explosion in history, after the Trinity test.
  Little Boy was developed by Lieutenant Commander Francis Birch's group at the Manhattan Project's Los Alamos Laboratory during World War II, a reworking of their unsuccessful Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon, but it derived its explosive power from the nuclear fission of uranium-235, whereas Thin Man was based on fission of plutonium-239. Fission was accomplished by shooting a hollow cylinder of enriched uranium onto a solid cylinder of the same material by means of a charge of nitrocellulose propellant powder.
context_section_description: The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. L-1, L-2, L-5, and L-6 were expended in test drops. The first drop test was conducted with L-1 on 23 July 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as Big Stink, piloted by Colonel Paul W. Tibbets, the commander of the 509th Composite Group. Two more drop tests over the sea were made on 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as Jabit. L-6 was used as a dress rehearsal on 29 July. The B-29 Next Objective, piloted by Major Charles W. Sweeney, flew to Iwo Jima, where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on 31 July, but this time L-6 was reloaded onto a different B-29, Enola Gay, piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb.
caption: Little Boy in the bomb pit on Tinian island, before being loaded into Enola Gay's bomb bay. A section of the bomb bay door is visible on the top right.
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