Warner Anderson (Capt. William S. Parsons, USN)
Brian Donlevy (Maj.-Gen. Leslie R. Groves)
Art Baker (Harry S. Truman)
Robert Walker (Col. Jeff Nixon)
Trevor Bardette (Clinic Doctor)
Tom Drake (Matt Cochran)
James Bush (Dr. Ernest O. Lawrence)
Audrey Totter (Jean O'Leary)
Joseph Calleia (Dr. Enrico Fermi)
Hume Cronyn (Dr. J. Robert Oppenheimer)
Huntz Hall (Brehon Somervel)
Edward Earle (Charles G. Ross)
Frank Ferguson (Dr. James B. Conant)
Victor Francen (Dr. Marre)
John Gallaudet (Dr. Leo Szilard)
Jonathan Hale (Dr. Vannevar Bush)
John Hamilton (Dr. Harold C. Urey)
Paul Harvey (Lieutenant General W.D. Styer)
Hurd Hatfield (Dr. John Wyatt)
Richard Haydn (Dr. Chisholm)
Larry Johns (Quaker Scientist)
Robert Emmett Keane (Dr. Rand)
John Litel (K.T. Keller)
Norman Lloyd (Dr. Troyanski)
Barry Nelson (Col. Paul Tibbets, Jr.)
Damian O'Flynn (C.D. Howe)
Henry O'Neill (Gen. Thomas F. Farrell)
Moroni Olsen (Dr. Arthur H. Compton)
Tom Stevenson (Dr. E.P. Winger)
Ludwig Stossel (Dr. Albert Einstein)
Godfrey Tearle (Franklin D. Roosevelt)
Charles Trowbridge (Walter S. Carpenter Jr.)
Nella Walker (Grace Tully)
Frank Wilcox (Dr. W.H. Zinn)
William Wright (Colonel John Lansdale)
Beverly Tyler (Ann Cochran)
Jim Davis (Pilot at Tinian)