Philip Morrison is a physicist who joined the Manhattan Project in 1942, and went on to advocate nuclear nonproliferation. Asked why he left Los Alamos after returning from Japan after the war, he responds: One nuclear war was enough. He recalls that the 1949 Soviet test confirmed the view of many scientists that in the absence of an international agreement an arms race will ensue. He charges that espionage had little to do with the Soviet success, and that it had real meaning only in the political sphere, allowing for contrived justification[s] for moving ahead with advances in nuclear weaponry although he believes the hydrogen bomb was under development before the exposure of the first spy cases.