Two identical reactors , D Reactor and F reactor , came online in December 1944 and February 1945 , respectively . By April 1945 , shipments of plutonium were headed to Los Alamos every five days , and Hanford soon provided enough material for the bombs tested at Trinity and dropped over Nagasaki . Throughout this period , the Manhattan Project maintained a top secret classification . Until news arrived of the bomb dropped on Hiroshima , fewer than one percent of Hanford 's workers knew they were working on a nuclear weapons project . General 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 . " Initially six reactors or " piles " were proposed , when the plutonium was to be used in the gun-type Thin Man bomb . In mid-1944 a simple gun-type bomb was found to be impractical for plutonium , and the more advanced Fat Man bomb , an implosion device , required less plutonium . The number of piles was reduced to four and then three ; and the number of chemical separation plants from four to three
Trinity
Trinity (nuclear test)
Hanford Site