The Mark 6 atomic bomb was similar in size and general design to the Mark 3 “Fat Man”—the bomb that was dropped on Nagasaki, Japan, on August 9, 1945—though with a higher maximum yield (160 kilotons). It was designed by scientists at Los Alamos National Laboratory, which had been established in 1943 as Site Y of the Manhattan Project for the single purpose of designing and building an atomic bomb.