Paul Frees

Self - Narrator (voice)

Jon Else

Interviewer

J. Robert Oppenheimer

Self (archive footage)

Hans Bethe

Self

Frank Oppenheimer

Self

Haakon Chevalier

Self

Robert Serber

Self

Freeman Dyson

Self

Leslie Groves

Self (archive footage)

Joseph McCarthy

Self (archive footage)

Isidor Isaac Rabi

Self

Harry S. Truman

Self (archive footage)