Chain Reaction

Construction on CP-1 halted at the fifty-seventh layer on December 1, 1942, when measurements indicated the pile would become self-sustaining once the control rods were withdrawn. On Wednesday, December 2, Fermi and his colleagues gathered on the balcony of the West Stand squash court to complete their test of the reactor. After tests in the morning and a break for lunch, the last control rod was slowly withdrawn until the "critical," or self-sustaining, level was reached. The scientists then watched the reactor operate for twenty-eight minutes before reinserting the rod and stopping the reaction. CP-1, the world’s first nuclear reactor, was an operational success. Arthur H. Compton telephoned Harvard University president James B. Conant, a member of the Manhattan Project Military Policy Committee, to convey the news: "The Italian navigator has just landed in the New World."