Paul Newman
Gen. Leslie R. Groves
Dwight Schultz
J. Robert Oppenheimer
Bonnie Bedelia
Kitty Oppenheimer
John Cusack
Michael Merriman
Laura Dern
Kathleen Robinson
Ron Frazier
Peter de Silva
John C. McGinley
Richard Schoenfield
Natasha Richardson
Jean Tatlock
Ron Vawter
Jamie Latrobe
Michael Brockman
William "Deke" Parsons
Del Close
Dr. Kenneth Whiteside
John Considine
Robert Tuckson
Allan Corduner
Franz Goethe
Joe D'Angerio
Seth Neddermeyer
Jon DeVries
Johnny Mount
James Eckhouse
Robert Harper
Todd Field
Robert Wilson
Mary Pat Gleason
Dora Welsh
Clark Gregg
Douglas Panton
Péter Halász
George Kistiakowsky
Gerald Hiken
Leo Szilard
Arthur Holden
Oakridge Doctor
Ed Lauter
Whitney Ashbridge
Donald MacKechnie
James Tuck
Madison Mason
Boris Pash
Krzysztof Pieczyński
Otto Frisch
Don Pugsley
Bronston
Logan Ramsey
Brehon Somervell
Fred Thompson
Melrose Hayden Barry
Jim True-Frost
Donald Hornig
Barry Yourgrau
Edward Teller
Marek Alboszta
Scientist
Steven Baigelman
Dr. Avenell
Frank Benettieri Jr.
Messenger
Roger Cubicciotti
Frank Oppenheimer
Franco Cutietta
Enrico Fermi
Robert Peter Gale
Dr. Louis Hempelman
Wesley Harrison
Peter Oppenheimer
Brent Harrison
Peter Oppenheimer
Tom McFarlane
Scientist
David C. Parnes
Raincoat Man
Allen Poirson
Harold McDonald
David Politzer
Robert Serber
Bill Rubenstein
Times Reporter
Ken Strausbaugh
Observation Officer
Walter Sullivan
Henry Stimson
Brian Wandell
Dennis Talmudge
John Williams
Mack Stoddard
Walker Edmiston
(voice)
Matthew Faison
(voice)
Stan Jones
(voice)
Alan Oppenheimer
(voice)