Naval History and Heritage Command

National Museum of the U.S. Navy

Little Boy - Hiroshima - August 6, 1945

The atomic bomb used at Hiroshima, Japan, on August 6, 1945, was "Little Boy".   The bomb was dropped by a USAAF B-29 bomber, Enola Gay, piloted by U.S. Army Air Force Colonel Paul Tibbets, Jr.   The bomb weighed 9,000 pounds and had a diameter of only 28 inches.  The gun-type weapon possessed the power of 26,000,000 pounds of high explosives.  Nuclear fission was achieved by the collision of two parts of active material (Uranium-235).  A U-235 projectile fired down a gun barrel collided with a stationary element, causing a mass increase leading to nuclear fission.  Little Boy was dropped untested.  Previously, on July 26, the bomb, along with "Fat Man" was transported to Tinian Island by USS Indianapolis (CA-35) for final assembly.  Four days later, Japanese submarine, I-58, sank Indianapolis, northeast of Leyte. 

A replica of Little Boy can be found at "In Harm's Way: Pacific" exhibit area in the National Museum of the Navy, Bldg. 76. 

Image:  77-BT-91:  Tinian Island, August 1945.  Boeing B-29 Superfortress, Enola Gay, returns after the strike Hiroshima, August 6, 1945.  Note the aircraft entering hard sand.  Official photograph of the Office of Chief of Engineers, now in the collections of the National Archives.