Just before dawn on 16 July 1945, the area selected for the Trinity test – the desolate Jornada del Muerto region of New Mexico – no longer swarmed with activity, as it had in the past several weeks. The thunder-storms that had worried Groves and Oppenheimer through the night had stopped. The scientists, who had worked almost nonstop in preparing for the first atomic bomb test, waited tensely for the test to begin.

Arranging their apparatuses around the gadget – ionization chambers, seismographs, motion picture cameras, and other devices – they prepared to record physical aspects of the explosion: light, heat, neutrons, gamma rays, and other features. The data would indicate what to expect of combat atomic bombs and how to achieve the most destruction. But even the most careful preparations could not guarantee a successful test, because the weather had to be just right to prevent heavy fallout from reaching populated areas. Completing the test on schedule became of paramount importance when President Harry S. Truman announced that he would meet with Churchill and Stalin at Potsdam on 16 July 1945.

The Experimental Program

Because only a limited number of measurements could be taken at Trinity, the ones to be selected became a critical topic of discussion. A panel consisting of Fussell, Moon, Bernard Waldman, and Victor Weisskopf was assembled to evaluate proposals. Data were needed on both the performance and the effects of the weapon.