DuPont commenced construction of the plutonium semiworks at the Clinton Engineer Works in Oak Ridge on February 2, 1943. The reactor went critical on November 4, 1943, and produced its first plutonium in early 1944. It supplied the Los Alamos Laboratory with its first significant amounts of plutonium, and its first reactor-bred product. Studies of these samples heavily influenced bomb design. The reactor and chemical separation plant provided invaluable experience for engineers, technicians, reactor operators, and safety officials who then moved on to the Hanford site. X-10 operated as a plutonium production plant until January 1945, when it was turned over to research activities, and the production of radioactive isotopes for scientific, medical, industrial and agricultural uses. It was shut down in 1963 and was designated a National Historic Landmark in 1965.