When Oppenheimer reorganized the laboratory in August 1944 to focus on the development of an implosion-type nuclear weapon, Wilson became head of R (Research) Division. As such he had four groups reporting to him: the Cyclotron Group (R-1), still headed by himself; the Electrostatic Group (R-2), headed by John H. Williams; the D-D (Deuterium-Deuterium) Group (R-3), headed by John H. Manley; and the Radioactivity Group (R-4), headed by Emilio G. Segrè. In March 1945, R Division acquired the additional responsibility of developing instrumentation for the Trinity nuclear test in July 1945. Wilson helped stack boxes of explosives for the 100-ton test that preceded it. At Los Alamos, he was also active in community affairs, serving on the town council.