Blueprints of the Hiroshima Atomic Bomb with handwritten explanation of its components by the Weapons Officer of the Hiroshima Mission

Little Boy was the code name of the atomic bomb which was dropped on Hiroshima, on August 6, 1945 by the 12-man crew of the B-29 Superfortress Enola Gay. Here we have a black and white copy of a Blue print showing the first atomic bomb with handwritten explanations of the components and how it works, in the hand of a crew member who dropped this bomb on Hiroshima, Enola Gay's Weapons Test Officer Jeppson. Jeppson was one of only 2 men who was both at Los Alamos during the development and testing of the bomb and also on board the Enola Gay when it dropped the bomb. Jeppson has made handwritten notations showing where a bullet of U235 shoots into a mass (truncated) of U235 to create a the atomic explosion. He writes on the blueprint, pointing out where the "uranium bullet" is, that shoots in "the uranium target ring" and explanations on how it worked.

The design was a very conservative one that was as certain to work as any untested device can be. The design was complete by February 1945 and the actual bomb was ready for combat use by early May, 1945 - except for the U-235 pit. The Little Boy design used the gun method to explosively force a sub-critical mass of uranium-235 and three U-235 target rings together into a supercritical mass, initiating a nuclear chain reaction. This was accomplished by simply shooting one piece of the uranium the "projectile U235" into the other, namely, the "target U235", by means of a chemical explosives.

Here Morris Jeppson, the Weapons Test Officer of the Enola Gay, has made handwritten notations explaining the main different parts of this Atomic Bomb, he writes: "Little Boy Bomb Weight about 5 tons". He draws arrows, labeling the "target U235" where the projectile 235 should hit. He points out the "hook to hang bomb in B29 Bomb Bay" that held the Bomb to the Enola Gay , the write "projectile U235" pointing to the bullet of U235 that will shout into the target .

On the margin he explains in his hand: "The design of Little Boy used the gun assembly method. The bullet of U235 impacting the target of U235 produces a critical mass in a very short period of time - and the heavy nose casing contains critical conditions long enough for the nuclear reaction to proceed. During the flight I removed 3 green electrical plugs and replaced them with red coded plugs. This allowed the detonation voltage to go from fusing to the explosive that fired the projectile of U235 into the target of U235 when the bomb reached about 1500 feet above Hiroshima. Underneath his explanation, he signs "Morris Jeppson/ Weapons Test Officer/ Enola Gay Mission/ HIROSHIMA - 6 Aug. 1945" .

The bomb was armed in flight, then Jeppson removed the safety plugs as describes on the document and as such was the last to touch Little Boy before it was dropped at approximately 8:15 a.m. (JST). Approximately 70,000 people were killed as a direct result of the blast, and a similar number were injured. Measure approx. 18" x 24". In excellent condition. (Inventory #: 19344)