In July 1944, Oppenheimer abandoned the Thin Man gun design in favor of an implosion-type weapon; a smaller version of Thin Man became Little Boy. Using chemical explosive lenses, a sub-critical sphere of fissile material could be squeezed into a smaller and denser form. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time. In August 1944, Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion. He concentrated the development efforts on the gun-type device, but now with a simpler design that only had to work with highly enriched uranium, in a single group. This device became Little Boy in February 1945. After a mammoth research effort, the more complex design of the implosion device, known as the "Christy gadget" after Robert Christy, another student of Oppenheimer's, was finalized as Fat Man in a meeting in Oppenheimer's office on February 28, 1945.