J. Robert Oppenheimer’s June 7, 1949, testimony before the House Un-American Activities Committee exposed the perilous gap between his wish to cooperate with investigators and his understanding of what his words could do to other people. In a closed session ostensibly concerned with his role as chairman of the Atomic Energy Commission’s General Advisory Committee, he answered questions about political affiliations among scientists and former students. His performance left the congressmen impressed; its leaked account, especially his statements about Bernard Peters, threatened a colleague’s standing and forced Oppenheimer’s friends to confront what he had said.

Background and Setting

Oppenheimer had reason to be apprehensive. He had received a subpoena and knew that one of the committee members, Representative Harold Velde, had been an FBI agent who investigated the University of California Radiation Laboratory during the war. A short time earlier, Oppenheimer had spoken with former students David Bohm and Giovanni Rossi Lomanitz. He later described that exchange as a brief conversation in which he advised them to tell the truth. The scrutiny of his students and associates was therefore not abstract: the committee’s inquiry reached into the political histories of people he had taught and known.

On June 7, six congressmen, including Richard Nixon, questioned him in executive session. Oppenheimer appeared as an AEC adviser, but the committee was interested in alleged atomic espionage and Communist activity, not primarily in nuclear policy. He chose not to bring a personal lawyer. Instead, he brought Joseph Volpe and introduced him as the AEC’s general counsel. Over the next two hours, he was cooperative and forthcoming, apparently hoping not to seem defensive.

Questions About Scientists and Associates

The questioning began with whether Oppenheimer knew that a Communist cell existed among scientists at the Radiation Laboratory. He denied knowing of one. Asked about his former student Joseph Weinberg, he denied knowing before the war that Weinberg was a Communist, adding that Weinberg’s expressed views after the war were not Communist-line views. He acknowledged that Rossi Lomanitz had been dismissed from the laboratory and inducted into the Army because of what he called an “unbelievable indiscretion.” He also confirmed that Weinberg was Lomanitz’s friend, that Irving David Fox had been active in organizing a union inside the laboratory, and that Kenneth May was an avowed Communist.

The questioning about Peters proved more consequential. Asked whether he had described Peters to Los Alamos security officers as “a dangerous man and quite red,” Oppenheimer admitted that he had. He explained that Peters had belonged to the German Communist Party, fought in street battles against the Nazis, and escaped Dachau concentration camp by “guile.” Oppenheimer also said that Peters had denounced the Communist Party in the United States as insufficiently committed to overthrowing the government by force and violence. When asked how he knew about Peters’s German Party membership, Oppenheimer answered, “Among other things, he told me.”

Oppenheimer’s account drew on things he said Peters had told him, but it also joined those statements to a damaging interpretation of Peters’s conduct. In a conversation the previous month, Samuel Goudsmit had asked whether Oppenheimer still thought Peters dangerous. Oppenheimer had reportedly replied, “Just look at him. Can’t you tell he can’t be trusted?” The hearing thus did not merely revisit an old security judgment: it made Oppenheimer’s continuing suspicion of a former student part of an official inquiry.

He also repeated his account of the Chevalier affair. Asked whether Haakon Chevalier was a Communist, Oppenheimer called him “the prize example of a parlor pink,” while saying that he did not know whether Chevalier belonged to the Party. He recounted that Chevalier had told him of George C. Eltenton’s idea for communicating scientific information to the Soviet government, and that Oppenheimer had responded forcefully against involvement. He said Chevalier had known nothing about the atomic bomb until it exploded over Hiroshima. Oppenheimer denied that anyone else had approached him for atomic information, without disclosing the different version involving several scientists that he had given to Boris Pash in 1943. That earlier conversation had been recorded without Oppenheimer’s knowledge and would remain in his security file, leaving his later denial and his earlier account in unresolved tension.

A Boundary Around His Brother

Oppenheimer was willing to name former students and describe the politics of friends, but he drew a line when asked about his brother’s past membership in the Communist Party. He told the committee, “I will answer the questions you put to me. I ask you not to press these questions about my brother.” He added that the committee could ask his brother directly and that he would answer if required, but begged the members not to make him do so. The counsel withdrew the question.

That refusal stood out against the rest of his testimony. Oppenheimer had otherwise tried hard to satisfy the committee, answering questions and supplying names where he could. His appeal on behalf of his brother showed that cooperation was not unlimited; family loyalty remained a boundary he asked the investigators to respect. The committee’s decision to withdraw the question spared him from crossing it in that session, but did not erase the contrast between his disclosure of other people’s histories and his reluctance to expose his brother’s.

Praise, Leak, and Consequences

At the close of the session, Nixon said he was “tremendously impressed” with Oppenheimer and “mighty happy” with his position in the atomic program. Volpe was astonished by how coolly Oppenheimer had handled the questioning, saying that Robert seemed determined to charm the congressmen. All six legislators came down to shake the famous scientist’s hand. Oppenheimer emerged from the hearing without immediate injury to his own standing, perhaps reinforcing his belief that his public prominence offered protection.

Peters, who testified the following day, did not have the same protection. He denied membership in the Communist Party in Germany or the United States and denied that his wife, Hannah Peters, had belonged to it. A week after Oppenheimer’s appearance, the closed-session testimony was leaked to the Rochester Times-Union. Its headline foregrounded Oppenheimer’s description of Peters as “Quite Red,” while the report also repeated the account of Peters’s escape from Dachau and his supposed advocacy of armed revolution. Peters feared for his job and publicly disputed the claims. He said he had admired the resistance to the Nazis and those who died in the concentration camp, but denied ever telling Oppenheimer that he had been a Communist. He acknowledged unorthodox views, including opposition to racial discrimination and support for socialism, while insisting that he was not a Communist.

Peters wrote to Oppenheimer with the newspaper clipping and challenged both the account of his politics and the story of his supposed street fighting. Oppenheimer, disturbed by the report, contacted Peters’s lawyer and asked that a message be passed on: he wanted to speak with Peters and believed the newspaper had misrepresented what he had said. Meanwhile, Frank Oppenheimer, Hans Bethe, and Victor Weisskopf expressed their dismay and urged him to set the record straight and do what he could to prevent Peters’s dismissal. The episode turned a private, closed-door hearing into a public injury to a former student. The praise Oppenheimer received from the committee and the damage Peters faced were immediate, contrasting outcomes of the same testimony.