Chapter Four THE CAST… ANOTHER HOLLYWOOD RECORD THE NEXT task facing the film makers was the immense one of casting the story's record-making 212 speaking roles. A few months earlier, before the return from service of many of Hollywood's leading actors, it would have been impossible, All but four of the roles are played by men.   Adding to the difficulty of this job twas the fact that a majority of the roles were depicting living personalities, the largest number ever arrayed in one film story. Even the fictional characters had to be cast with great care. because of what they represented.   Prominent persons to be portrayed on the screen ranged from two Presidents of the United States ~ Harry S. Truman and the late Franklin Delano Roosevelt - to leaders of every phase of the vast atomic project. These included Generals Brehon Somervell. W. D. Styer, Groves and Farrell, Rear Admiral William S. Parsons and Colonel John Lansdale on the armed forces side: Professor Albert Einstein, Professor Enrico Fermi, Dr. J. Robert Oppenheimer, brilliant University of California physicist who headed the Los Alamos development and supervised the New Mexico bomb test, Dr. Vannevar Bush, director of the Office of Scientific Research and Development.   Dr. Arthur Compton, director of the Metallurgy Project at the University of Chicago, Dr. James B. Conant, President of Harvard University, Dr. Ernest O. Lawrence, director of the Radiation Laboratory at the University of California and inventor of the famed cyclotron and many others from the world of science; K. T. Keller of Chrysler Motors, W. S. Carpenter, Jr.. of the du Pont Company, James A. Rafferty of Union Carbide Company and Harry A. Winne of General Electric among the industrialists.   In every case, the script was shown to I these men and approved. Frequently' they proffered suggestions for augmenting scenes and these were incorporated into the screenplay, Almost without exception,. actors were selected of the same physical make-up and type as the men they were to depict. although the first requirement always was proved acting abilitty.