<P> The 1943 Quebec Agreement merged the nuclear weapons projects of the United Kingdom and Canada , Tube Alloys and the Montreal Laboratory , with the Manhattan Project , under the direction of Major General Leslie R. Groves , Jr. , of the U.S. Army Corps of Engineers . Groves appointed J. Robert Oppenheimer to organize and head the project 's Los Alamos Laboratory in New Mexico , where bomb design work was carried out . Two types of bombs were eventually developed , both named by Robert Serber. Little Boy was a gun - type fission weapon that used uranium - 235 , a rare isotope of uranium separated at the Clinton Engineer Works at Oak Ridge , Tennessee . The other , known as a Fat Man device , was a more powerful and efficient , but more complicated , implosion - type nuclear weapon that used plutonium created in nuclear reactors at Hanford , Washington . </P>
what is the name of the two atomic bombs dropped on japan
Little Boy Fat Man