At its December 6, 1941 meeting, the National Defense Research Committee resolved to proceed with an all-out effort to produce atomic bombs. This decision was given urgency by the Japanese attack on Pearl Harbor the following day that brought the United States into World War II. It was formally approved by Roosevelt in January 1942. Arthur H. Compton from the University of Chicago was appointed head of research and development. Against Szilard's wishes, Compton concentrated all the groups working on reactors and plutonium at the Metallurgical Laboratory of the University of Chicago. Compton laid out an ambitious plan to achieve a chain reaction by January 1943, start manufacturing plutonium in nuclear reactors by January 1944, and produce an atomic bomb by January 1945.