On 20 December, soon after the Japanese attack on Pearl Harbor that brought the United States into the war, Compton was placed in charge of the plutonium project. Its objectives were to produce reactors to convert uranium to plutonium, to find ways to chemically separate the plutonium from the uranium, and to design and build an atomic bomb. Although a successful reactor had not yet been built, the scientists had already produced several different but promising design concepts. It fell to Compton to decide which of these should be pursued. He proposed an ambitious schedule that aimed to achieve a controlled nuclear chain reaction by January 1943, and to have a deliverable atomic bomb by January 1945.