Brien McMahon

Brien McMahon emerges as a forceful advocate of developing the hydrogen bomb at speed, opposed to the possibility that the United States might hold back while the Soviet Union pursued the weapon. His reaction to the General Advisory Committee’s case against a crash program was not merely a disagreement over military design: it reflected a conviction that war with the Soviet Union was inevitable and that delay could be fatal. In the book’s account, McMahon helps mark the point where technical and moral arguments about the Super collided with the political demand to appear ready for the worst.

Position in the Atomic Debate

McMahon was a senator involved in the Joint Committee on Atomic Energy and a prominent proponent of moving forward with the hydrogen bomb. The dispute became especially sharp after the Soviet atomic test prompted a three-day General Advisory Committee meeting in October 1949. Chaired by J. Robert Oppenheimer, the committee heard expert testimony and debated whether the United States should embark on a crash program. Its members considered the weapon’s military value alongside the consequences of a thermonuclear war and the danger that developing the Super would accelerate Soviet development rather than deter it.

The committee’s objections were concrete. A weapon that might yield 100 million tons of TNT, compared with 15,000 tons for the Hiroshima bomb, could destroy hundreds of square miles and risk becoming a weapon of genocide. The majority argued that a large American stockpile of atomic bombs would still permit effective retaliation if the Soviet Union acquired a Super. They also proposed strengthening conventional forces in Western Europe and developing smaller tactical atomic weapons instead. Their argument was for an arsenal designed to meet specific military needs, not an open-ended contest in ever-larger weapons.

McMahon rejected that restraint. Responding to the committee’s report, he told Teller that it made him sick. He had come to believe war with the Soviet Union was inevitable and told David Lilienthal that the United States should destroy its adversary before it could do the same to America. His language expressed the alarm behind his policy: the possibility that the Soviet Union might gain the weapon first outweighed the committee’s warnings about genocide, arms-race dynamics, and the risks of building the Super.

Confrontation over the Super

On January 30, 1950, while in Washington for a General Advisory Committee meeting, Oppenheimer went to a special Joint Committee on Atomic Energy meeting that McMahon had called to discuss the hydrogen bomb. Oppenheimer knew McMahon was lobbying President Harry S. Truman to approve a crash program and that his own opposition would be unwelcome. He nevertheless said it would be cowardly not to appear and answer the legislators’ questions.

McMahon’s meeting put the central dilemma directly to Oppenheimer: what if the Soviet Union acquired the Super and the United States did not? Oppenheimer answered that either outcome would leave the United States badly off. Building the weapon, he argued, would help accelerate Soviet development; the point of refusing the race was not to pretend the danger was absent, but to avoid making that danger worse. Asked whether a hydrogen-bomb war could make Earth unfit for human habitation, Oppenheimer interjected, “Pestiferous, you mean?” He then stressed that he was more concerned about humanity’s moral survival. He presented the case calmly, but left without changing anyone’s mind.

The meeting preceded a final White House decision. On January 31, McMahon’s pressure formed part of the political setting in which Lilienthal, Secretary of State Dean Acheson, and Defense Secretary Louis Johnson went to see Truman. Acheson believed domestic politics would make delay intolerable; Johnson told Lilienthal, “We must protect the president.” Truman cut off Lilienthal’s presentation to ask whether the Soviet Union could build the weapon. Told that it could, he ordered the United States to go ahead. The book presents this decision as shaped not only by assessments of national security but also by the pressure to demonstrate resolve at home.

Building Political Support

McMahon’s influence also reached into the committee’s staffing. After seeing a Yale newspaper advertisement urging Truman to issue the Soviet Union an atomic ultimatum—“Let Stalin Decide: atomic war or atomic peace”—he hired its young conservative supporter William Liscum Borden as an aide to the Joint Committee on Atomic Energy. Borden was already preoccupied with the Soviet threat and the prospect of a nuclear attack on the United States. His recruitment placed an alarmed, weapons-focused staff member within the congressional body overseeing atomic policy.

Borden’s suspicions of Oppenheimer developed over time. He had first encountered the physicist at a 1949 General Advisory Committee meeting, where Oppenheimer criticized proposals for a nuclear-powered bomber and civilian nuclear plants. After the Soviet test and the dispute over the Super, Borden came to view Oppenheimer’s influence with increasing suspicion, a view encouraged by Lewis Strauss. McMahon’s documented role here is specific: he hired Borden after noticing the ultimatum advertisement. The account does not establish that McMahon directed Borden’s later suspicions or shared every one of his conclusions.

The Expanding Security Controversy

On February 6, 1950, McMahon was present when FBI Director J. Edgar Hoover testified before the Joint Committee. Although Hoover had ostensibly come to brief the committee about Klaus Fuchs, he spoke at length about Oppenheimer. McMahon and Representative Henry “Scoop” Jackson learned from Hoover of Haakon Chevalier’s 1943 approach to Oppenheimer, in which Chevalier had raised the possibility of sharing scientific information with the Soviet Union, then a wartime ally. Hoover reported that Oppenheimer had rejected the overture. Borden, however, found the episode incriminating and began to suspect that Oppenheimer’s opposition to the Super arose from communist loyalty.

The juxtaposition is consequential but does not make the distinctions disappear: Hoover’s account described a rejected approach, while Borden interpreted the episode through his growing suspicion of Oppenheimer. McMahon’s presence links the congressional debate over hydrogen-bomb policy with the emerging security controversy around the scientists who challenged it. Later, Oppenheimer’s opposition to the Super would be included among the charges against him, framed as having slowed its development. The book’s portrayal of McMahon’s earlier advocacy helps explain the political climate in which opposition to rapid weapons development could be treated not simply as a disputed judgment about strategy, but as a matter of loyalty and national security.