Lansdale’s security interviews with Oppenheimer

John Lansdale’s security relationship with J. Robert Oppenheimer was built through interviews in which suspicion and confidence repeatedly coexisted. Lansdale was responsible for assessing political and security concerns surrounding the Manhattan Project’s scientific director. He took those concerns seriously, but unlike officers who wanted Oppenheimer removed, he came to trust him. Their most consequential conversations turned on a difficult distinction: Oppenheimer would discuss political affiliations and project security, yet resisted naming an intermediary in a suspected espionage approach because he believed that doing so would unfairly involve people he considered innocent.

An assessment shaped by suspicion

Shortly after meeting Oppenheimer, Lansdale prepared a two-page memorandum for General Leslie Groves. It catalogued organizations the FBI regarded as political “front” groups and Oppenheimer’s associations with people identified as communists or suspected communists. The memorandum included Oppenheimer’s friendship with Jean Tatlock and Haakon Chevalier, as well as an informant’s report that Oppenheimer and his brother Frank were regularly registered with the Communist Party. Lansdale’s inventory registered the breadth of the security concerns; it did not, however, lead him to recommend Oppenheimer’s dismissal.

Instead, in July 1943, Lansdale advised Groves to tell Oppenheimer that the Communist Party was trying to obtain information about the Manhattan Project and that the Army was investigating people suspected of following the Party line. Lansdale proposed using Oppenheimer’s access and knowledge to help identify those involved. In practical terms, keeping him as scientific director came with pressure to become an informer. The approach placed confidence in Oppenheimer’s value to the project alongside suspicion of his past and present associations.

Lomanitz and the question of loyalty

The tension became more personal when Oppenheimer tried to intervene on behalf of his protégé Giovanni Rossi Lomanitz. After Lomanitz was called for an Army physical examination, Oppenheimer sent a cable protesting that a serious mistake was being made and that Lomanitz was the only person at Berkeley able to take on an important responsibility. Lomanitz was nevertheless inducted. A few days later, Lansdale visited Oppenheimer’s office and warned him not to make further efforts to help the young physicist, whose political activity, Lansdale said, could not be overlooked.

Oppenheimer was angry. He said Lomanitz had promised to abstain from political work if he joined the bomb project. Their disagreement then widened into a discussion of Communist Party membership and security. Lansdale said his concern was whether classified information reached unauthorized people, not a person’s political beliefs. Oppenheimer rejected that as sufficient. He argued that active Party membership raised a problem of divided loyalty because Party discipline was incompatible with complete loyalty to the project. He distinguished current members from former members, some of whom, he acknowledged, worked at Los Alamos.

Lansdale understood Oppenheimer’s carefully qualified remarks as an indirect admission that he himself had once belonged to the Party and had ended his connection when he began this work. He thought Oppenheimer seemed anxious to explain himself, subtle in his allusions, and sincere. Though the two men would continue to spar over security, Lansdale came away believing that Oppenheimer was loyal and devoted to the United States. That judgment mattered: Lansdale could accept the seriousness of the political associations without treating them as proof of disloyalty.

The Eltenton approach and withheld names

Oppenheimer’s own concern about security sharpened after the Lomanitz episode. He suspected that Lomanitz’s trouble might stem from union organizing and recalled that George C. Eltenton, a Shell engineer, had been active in the same labor organization. Eltenton had previously prompted Chevalier to approach Oppenheimer about passing project information to the Soviet Union. What Oppenheimer had first dismissed as ridiculous now seemed serious. He informed Army authorities about Eltenton and, on August 25, 1943, identified him to the Radiation Laboratory’s security officer as someone who should be watched.

When Army counterintelligence questioned him, Oppenheimer named Eltenton but withheld the identity of the intermediary who had approached him. He described the intermediary as innocent and said the people contacted had rejected the approach. In a September 12 conversation, Lansdale—having read the transcript of Oppenheimer’s earlier interrogation—set out to clarify what had happened. He acknowledged that he had not been entirely frank in previous conversations, then told Oppenheimer that the government had known since February that people were passing information about the project to the Soviet government. Oppenheimer appeared genuinely surprised, saying he had not known that and could recall only the earlier attempt.

Lansdale pressed the central question: how could Oppenheimer know that Eltenton had not approached other scientists? Oppenheimer admitted he could not know, but still resisted naming the intermediary or the other people involved. He said the additional names he knew did not seem to belong to anyone guilty of wrongdoing and described the approach as erratic and unsystematic. Withholding the intermediary’s name, he maintained, was justified by a sense of duty. The refusal was not a denial that security mattered; it was his judgment that naming people without evidence would draw the innocent into an investigation.

Oppenheimer did provide Lansdale with names when asked which Berkeley workers he thought were or had been Party members. He identified Giovanni Rossi Lomanitz and Joseph Weinberg as current members, named Jane Muir as a possible member, and said Charlotte Serber had once belonged to the Party. About Robert Serber, he said he thought membership was possible but did not know. Asked again to name people connected to the approach, however, he called it a “low trick” to implicate someone he would bet was uninvolved. The contrast was characteristic of their exchanges: Oppenheimer disclosed political information while drawing a moral boundary around allegations he considered unsupported.

A guarded, consequential trust

Two days later, on September 14, Lansdale and Groves spoke with Oppenheimer about Eltenton during a train journey from Cheyenne to Chicago. Oppenheimer said he would identify the intermediary only if ordered. He maintained that position when pressed again about a month later. Groves accepted his refusal, interpreting it as a schoolboyish belief that informing on a friend was wrong; Lansdale and Groves told the FBI they believed Oppenheimer was telling the truth.

That confidence did not erase the institutional pressure surrounding their relationship. Lansdale’s earlier strategy had contemplated drawing information from Oppenheimer, while the later interviews tested whether his account of the Eltenton approach could be trusted. The conversations were recorded, and the account Oppenheimer gave became part of a security file that would later sustain uncertainty about whether he had initially lied or subsequently changed his story. Lansdale’s personal belief in his sincerity therefore coexisted with an official record that could be used against him.

The relationship was neither simple friendship nor uncomplicated surveillance. Lansdale recognized the risks posed by Oppenheimer’s associations, but also encountered a scientist willing to discuss loyalty, distinguish current from former Party membership, and resist what he regarded as unjust accusations. Oppenheimer, in turn, continued to engage with Lansdale while learning that his interventions for colleagues and his own explanations could become security evidence. Their exchanges show trust forming inside, rather than outside, the machinery of wartime suspicion—and show how a principled refusal to name others could itself become an enduring source of doubt.