Ralph Lapp was completing his PhD in physics at the University of Chicago when he joined the Manhattan Project. After the war, he worked for the War Department and served as a scientific advisor there before leaving the government to start his own firm. Lapp went on to write several books and advocate for peaceful uses of nuclear energy. In this interview, he discusses how he stumbled upon Enrico Fermi’s team working under Stagg’s Field in December of 1942, and was hired on the spot to work on the development of the atomic bomb. Lapp recalls witnessing the 1946 Bikini nuclear tests, and discusses the controversy over the Lucky Dragon boat, caught into the fallout of one of 1954 Castle Bravo hydrogen bomb test. He examines how nuclear weapons have changed the course of human history.