1. Albert Einstein, writing in 1939 at the suggestion of fellow European emigre scientist, Leo Szilard. Many key figures in the US atomic program were European exiles who had escaped the Nazi regime.

2. The Manhattan Project. It was the largest single enterprise in the history of science. Work was done in 19 states and Canada. Other key sites include Chicago and the newly created cities of Oak Ridge, TN, Los Alamos, NM and Hanford, WA. The last two recently made news again when wildfires approached Nuclear storage facilities.

3. J. Robert Oppenheimer, who later opposed development of a hydrogen bomb on moral and technical grounds and was suspended from the Atomic Energy Commission as a security risk.

4. The Enola Gay

5. It was plutonium-based.