Paul Newman as Gen. Leslie R. Groves

Dwight Schultz as J. Robert Oppenheimer

Bonnie Bedelia as Kitty Oppenheimer

John Cusack as Michael Merriman

Laura Dern as Kathleen Robinson

Ron Frazier as Peter de Silva

John C. McGinley as Richard Schoenfield

Natasha Richardson as Jean Tatlock

Ron Vawter as Jamie Latrobe

Michael Brockman as William "Deke" Parsons

Del Close as Dr. Kenneth Whiteside

John Considine as Robert Tuckson

Allan Corduner as Franz Goethe

Joe D'Angerio as Seth Neddermeyer

Jon DeVries as Johnny Mount

James Eckhouse as Robert Harper

Todd Field as Robert Wilson

Mary Pat Gleason as Dora Welsh

Clark Gregg as Douglas Panton

Péter Halász as George Kistiakowsky

Gerald Hiken as Leo Szilard

Arthur Holden as Oakridge Doctor

Ed Lauter as Whitney Ashbridge

Donald MacKechnie as James Tuck

Madison Mason as Boris Pash

Krzysztof Pieczyński as Otto Frisch

Don Pugsley as Bronston

Logan Ramsey as Brehon Somervell

Fred Thompson as Melrose Hayden Barry

Jim True-Frost as Donald Hornig

Barry Yourgrau as Edward Teller

Marek Alboszta as Scientist

Steven Baigelman as Dr. Avenell

Frank Benettieri Jr. as Messenger

Roger Cubicciotti as Frank Oppenheimer

Franco Cutietta as Enrico Fermi

Robert Peter Gale as Dr. Louis Hempelman

Wesley Harrison as Peter Oppenheimer

Brent Harrison as Peter Oppenheimer

Tom McFarlane as Scientist

David C. Parnes as Raincoat Man

Allen Poirson as Harold McDonald

David Politzer as Robert Serber

Bill Rubenstein as Times Reporter

Ken Strausbaugh as Observation Officer

Walter Sullivan as Henry Stimson

Brian Wandell as Dennis Talmudge

John Williams as Mack Stoddard

Walker Edmiston as (voice)

Matthew Faison as (voice)

Stan Jones as (voice)

Alan Oppenheimer as (voice)