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National Museum of Nuclear Science & History

Gun Site

The Gun Site (TA-8-1) was where Manhattan Project scientists and engineers developed and tested the gun-type weapon design. The design for the “Little Boy” bomb dropped on Hiroshima on August 6, 1945, was developed here.

The gun design was straightforward. Basically, a “bullet” of nuclear material was fired at very high speed into a second nuclear mass, creating a critical mass. This released enormous energy with an immense explosion. Scientists were confident the design would work and the gun-type bomb was not tested before it was used against Japan.

The Gun Site had a large proving ground above the bunker-like buildings. Two Naval cannons were hidden from view by wooden housing on rails. The housing could be removed when the cannons were fired. The team observed the firings from the bunkers through a periscope mounted in a 45-foot tower. After a test firing, they retrieved the projectiles and analyzed the test results in a work area equipped with a camera room, darkroom and X-ray equipment. Work is underway to restore the facilities as they were during the Manhattan Project.

Los Alamos NM, 87544 US
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