---
title: "J. Robert Oppenheimer"
chunk: 8/17
source: "https://en.wikipedia.org/wiki/J._Robert_Oppenheimer"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:07:13.473219+00:00"
instance: "kb-cron"
---

At this point in the war, there was considerable anxiety among the scientists that the German nuclear weapons program might be progressing faster than the Manhattan Project. In a letter dated May 25, 1943, Oppenheimer responded to a proposal by Fermi to use radioactive materials to poison German food supplies. Oppenheimer asked Fermi whether he could produce enough strontium without letting too many in on the secret. Oppenheimer continued, "I think we should not attempt a plan unless we can poison food sufficient to kill a half a million men."
In 1943, development efforts were directed to a plutonium gun-type fission weapon called "Thin Man". Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure but could be created only in tiny amounts. When Los Alamos received the first sample of plutonium from the X-10 Graphite Reactor in April 1944, a problem was discovered: reactor-bred plutonium had a higher concentration of plutonium-240 (five times that of "cyclotron" plutonium), making it unsuitable for use in a gun-type weapon.
In July 1944, Oppenheimer abandoned the Thin Man gun design in favor of an implosion-type weapon; a smaller version of Thin Man became Little Boy. Using chemical explosive lenses, a sub-critical sphere of fissile material could be squeezed into a smaller and denser form. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time. In August 1944, Oppenheimer implemented a sweeping reorganization of the Los Alamos Laboratory to focus on implosion. He concentrated the development efforts on the gun-type device, but now with a simpler design that only had to work with highly enriched uranium, in a single group. This device became Little Boy in February 1945. After a mammoth research effort, the more complex design of the implosion device, known as the "Christy gadget" after Robert Christy, another student of Oppenheimer's, was finalized as Fat Man in a meeting in Oppenheimer's office on February 28, 1945.
In May 1945, an Interim Committee was created to advise and report on wartime and postwar policies regarding the use of nuclear energy. The Interim Committee established a scientific panel consisting of Oppenheimer, Arthur Compton, Fermi, and Lawrence to advise it on scientific issues. In its presentation to the Interim Committee, the panel offered its opinion not just on an atomic bomb's likely physical effects but also on its likely military and political impact. This included opinions on such sensitive issues as whether the Soviet Union should be advised of the weapon in advance of its use against Japan.

=== Trinity ===

In the early morning hours of July 16, 1945, near Alamogordo, New Mexico, the work at Los Alamos culminated in the test of the world's first nuclear weapon. Oppenheimer had code-named the site "Trinity" in mid-1944, saying later that the name came from John Donne's Holy Sonnets; he had been introduced to Donne's work in the 1930s by Jean Tatlock, who killed herself in January 1944.
Brigadier General Thomas Farrell, who was present in the control bunker with Oppenheimer, recalled:

Dr. Oppenheimer, on whom had rested a very heavy burden, grew tenser as the last seconds ticked off. He scarcely breathed. He held on to a post to steady himself. For the last few seconds, he stared directly ahead and then when the announcer shouted "Now!" and there came this tremendous burst of light followed shortly thereafter by the deep growling roar of the explosion, his face relaxed into an expression of tremendous relief.
Oppenheimer's brother Frank recalled Oppenheimer's first words as "I guess it worked."

According to a 1949 magazine profile, while witnessing the explosion Oppenheimer thought of verses from the Bhagavad Gita: "If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one ... Now I am become Death, the shatterer of worlds." In 1965 he recalled the moment this way:

We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, "Now I am become Death, the destroyer of worlds." I suppose we all thought that, one way or another.
Rabi described seeing Oppenheimer somewhat later: "I'll never forget his walk ... like High Noon ... this kind of strut. He had done it." Despite many scientists' opposition to using the bomb on Japan, Compton, Fermi, and Oppenheimer believed that a test explosion would not convince Japan to surrender. At an August 6 assembly at Los Alamos, the evening of the atomic bombing of Hiroshima, Oppenheimer took to the stage and clasped his hands together "like a prize-winning boxer" while the crowd cheered. He expressed regret that the weapon was ready too late for use against Nazi Germany.
On August 17, however, Oppenheimer traveled to Washington to hand-deliver a letter to Secretary of War Henry L. Stimson expressing his revulsion and his wish to see nuclear weapons banned. In October he met with President Harry S. Truman, who dismissed Oppenheimer's concern about an arms race with the Soviet Union and belief that atomic energy should be under international control. Truman became infuriated when Oppenheimer said, "Mr. President, I feel I have blood on my hands", responding that he (Truman) bore sole responsibility for the decision to use atomic weapons against Japan, and later said, "I don't want to see that son of a bitch in this office ever again."
For his services as director of Los Alamos, Oppenheimer was awarded the Medal for Merit by Truman in 1946.