By the time a fast-neutron fission laboratory was conceived early in 1942, theorists and experimentalists had made initial calculations for the bomb, including new estimates of critical mass and efficiency. Some progress had been made on designing methods for assembling the weapon and on a program for measuring nuclear constants central to bomb calculations. On the whole, however, research languished because of poor information exchange among the various groups involved, which were scattered throughout the United States. Oppenheimer, who replaced Gregory Breit as coordinator of the fast-fission project, recommended to Groves that the effort be centralized. Groves, who recognized the security benefits of centralization, readily complied, thereby setting in motion plans for establishing the Los Alamos Laboratory.

Groves and Oppenheimer took the first step toward creating the laboratory in early 1943 by recruiting many of the world's best scientists. The temporary nature of the project and the urgency of its mission aided the recruitment effort, but the task was complicated by the delicate issue of whether Los Alamos would be a military or a civilian establishment – an issue never formally resolved. The standard caricature of Oppenheimer as an other-worldly intellectual and Groves as a burly martinet highlights the misalignment between the military and scientific communities that joined in Project Y. Surprisingly, Oppenheimer and Groves developed a collaboration that was both congenial and fruitful.