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.