After the implosion design was frozen at the end of February 1945, the program shifted its emphasis from research to constructing actual bomb components, including explosive lenses, detonators, initiators, and the plutonium hemispheres. Kistiakowsky reported on X-Division's work in April: “One can now state with a reasonable degree of assurance that all major research and design gambles involved in the freeze of the program of the X-Division have been won. Progress is more and more determined by the rate of supply of manufactured items.” By May, he concluded, “The activities in X-Division have lost all semblance to research and have become so largely production and inspection and testing that their brief summary here seems impractical” (at which point his division progress reports stopped abruptly). However, most of the crucial components of the implosion gadget remained problematic, almost to the time of the Trinity test, and most underwent last-minute change.

The Cowpuncher Committee

Oppenheimer launched the final phase of Project Y's implosion effort with his appointment on 1 March 1945 of the powerful Cowpuncher Committee to “ride herd” on the program. Besides Oppenheimer, the members included Bethe, Kistiakowsky, Parsons, Bacher, Samuel Allison, Cyril Smith, and Kenneth Bainbridge. The committee oversaw eight major programs: (1) fabrication and inspection of explosive lenses; (2) design and construction of electric detonators and detonator circuits; (3) diagnostic tests to determine timing, compression, and symmetry; (4) research in chemistry and metallurgy; (5) study of the critical mass and time constant of the plutonium nuclear explosion; (6) design of the inner metal parts of the implosion assembly; (7) coordination of the Trinity program; and (8) assignment of shop priorities.