The K-25 Plant in Oak Ridge used the gaseous diffusion process to enrich uranium.
Gaseous Diffusion Process
The K-25 plant was an enormously ambitious and risky undertaking. A mile-long, U-shaped building, the K-25 plant was the world’s largest roofed building at the time. British scientists working on the “tube alloy,” code for the atomic bomb project, first advocated the gaseous diffusion method in March 1941. Because of the Nazi bombing of England, any production plants had to be located elsewhere.