The Manhattan Project: Making the Atomic Bomb

Reports on Trinity

Stalin arrived in Berlin a day late, leaving Stimson July 16 to mull over questions of postwar German administration and the Far Eastern situation. After sending Truman and Byrnes a memorandum advocating an early warning to Japan and setting out a bargaining strategy for Russian entry in the Pacific war, Stimson received a cable from George L. Harrison, his special consultant in Washington, that read:

Operated on this morning. Diagnosis not yet complete but results seem satisfactory and already exceed expectations. Local press release necessary as interest extends great distance. Dr. Groves pleased. He returns tomorrow. I will keep you posted.⁵¹

Stimson immediately informed Truman and Byrnes that the Trinity test had been successful. The next day Stimson informed Churchill of the test. The prime minister expressed great delight and argued forcefully against informing the Russians, though he later relented. On July 18, while debate continued over the wording of the surrender message, focusing on whether or not to guarantee the place of the emperor, Stimson received a second cable from Harrison:

Doctor has just returned most enthusiastic and confident that the little boy is as husky as his big brother. The light in his eyes discernible from here to Highhold and I could have heard his screams from here to my farm.⁵²

Translation: Groves thought the plutonium weapon would be as powerful as the uranium device and that the Trinity test could be seen as far away as 250 miles and the noise heard for fifty miles. Initial measurements taken at the Alamogordo site suggested a yield in excess of 5,000 tons of TNT. Truman went back to the bargaining table with a new card in his hand.

Further information on the Trinity test arrived on July 21 in the form of a long and uncharacteristically excited report from Groves. Los Alamos scientists now agreed that the blast had been the equivalent of between 15,000 and 20,000 tons of TNT, higher than anyone had predicted. Groves reported that glass shattered 125 miles away, that the fireball was brighter than several suns at midday, and that the steel tower had been vaporized. Though he had previously believed it impregnable, Groves stated that he did not consider the Pentagon safe from atomic attack.⁵³ Stimson informed Marshall and then read the entire report to Truman and Byrnes. Stimson recorded that Truman was "tremendously pepped up" and that the document gave him an entirely new feeling of confidence."⁵⁴ The next day Stimson, informed that the uranium bomb would be ready in early August, discussed Grove's report at great length with Churchill. The British prime minister was elated and said that he now understood why Truman had been so forceful with Stalin the previous day, especially in his opposition to Russian designs on Eastern Europe and Germany. Churchill then told Truman that the bomb could lead to Japanese surrender without an invasion and eliminate the necessity for Russian military help. He recommended that the President continue to take a hard line with Stalin. Truman and his advisors shared Churchill's views. The success of the Trinity test stiffened Truman's resolve, and he refused to accede to Stalin's new demands for concessions in Turkey and the Mediterranean.

On July 24 Stimson met with Truman. He told the President that Marshall no longer saw any need for Russian help, and he briefed the President on the latest S-1 situation. The uranium bomb might be ready as early as August 1 and was a certainty by August 10. The plutonium weapon would be available by August 6. Stimson continued to favor making some sort of commitment to the Japanese emperor, though the draft already shown to the Chinese was silent on this issue.

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