A recording was shown being made on audio reel-to-reel tape of Oppenheimer's telephone conversations during the early years at Los Alamos. Though developed in 1928 in Germany, escalating tensions in the 1930s caused Germany to keep its development secret. It did not exist in the United States at the time shown in the film. It was only after the war and the capture of this technology by the Allies that it came here to be developed into the form seen in the film.