The almost limitless energy of the atom was first harnessed in the United States, as scientists proved the basic physics of nuclear fission in a rudimentary reactor built in the floor of a squash court at the University of Chicago in 1942, and then harnessed that proven energy source in the form of atomic weapons used to end World War II. Scientists who accomplished this feat moved quickly after World War II to harness that power for peaceful uses, focusing primarily on electricity generation for industry, commerce, and household use.