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

Del Close

Dr. Kenneth Whiteside

John Considine

Robert Tuckson

Allan Corduner

Franz Goethe

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

Arthur Holden

Oakridge Doctor

Ed Lauter

Whitney Ashbridge

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

Robert Peter Gale

Dr. Louis Hempelman

Ken Strausbaugh

Observation Officer

Walker Edmiston

(voice)

Matthew Faison

(voice)

Stan Jones

(voice)

Alan Oppenheimer

(voice)