transmission line was not badly damaged. The Hanford Engineer Works was the only U.S. nuclear facility to come under enemy attack. Hanford provided the plutonium for the bomb used in the 1945 Trinity nuclear test. Throughout this period, the Manhattan Project maintained a top-secret classification. Fewer than one percent of Hanford's workers knew they were working on a nuclear weapons project. Groves noted in his memoirs that "We made certain that each member of the project thoroughly understood his part in the total effort; that, and nothing more." The existence and purpose of Hanford was publicly revealed through press releases on August 7 and 9, 1945, after the bombing of Hiroshima but before Hanford plutonium in a Fat Man bomb was used in the bombing of Nagasaki on August 9. Matthias was succeeded as area engineer by Colonel Frederick J. Clarke in January 1946. DuPont would soon be gone too. Carpenter asked to be released from the contract. Groves informed Robert P. Patterson, who had succeeded Stimson as Secretary of War on September 21, 1945, Groves's choice of replacement was General Electric (GE), which took over operations at Hanford on September 1, 1946, and accepted a formal control on September 30. On December 31, 1946, the Manhattan Project ended and control of the Hanford Site passed to the Atomic Energy Commission (AEC). The total cost of the Hanford Engineer Works up to that time was . Cold War Production problems GE inherited serious problems. Running the reactors continuously at full power had resulted in the Wigner effect, swelling of the graphite due to the displacement of the atoms in its crystalline structure by collisions with neutrons. This had the potential to buckle the aluminum tubes used for the fuel and control rods and disable the reactors completely if a water pipe ruptured. The polonium-210 used in the Fat Man's neutron initiators had a half-life of only 138 days, so it was essential to keep a reactor running or the weapons would be rendered inoperative. The Army therefore shut down BReactor on March 19. In August 1946 Franklin was informed that irradiating the feed to produce over 200 grams of plutonium per metric ton of uranium was resulting in too much undesirable plutonium-240 in the product. The power level on Dand FReactors was reduced, which also extended their useful life. Some experiments were conducted with annealing the graphite. It was found