(For other uses, see K25 (disambiguation).) K-25 was the codename given by the Manhattan Project during World War II for the project to produce enriched uranium for atomic bombs using the gaseous diffusion method. Originally the codename for the product, over time it came to refer to the project, the production facility located at the Clinton Engineer Works in Oak Ridge, Tennessee, the main gaseous diffusion building, and ultimately the site. When it was built in 1944, the four-story K-25 gaseous diffusion plant was the world's largest building, with over 1,640,000 square feet (152,000 m2) of floor space and a volume of 97,500,000 cubic feet (2,760,000 m3).