Washington, D.C., September 9, 2019 – Seventy years ago, on 9 September 1949, Director of Central Intelligence Admiral Roscoe Hillenkoetter handed President Harry Truman a carefully worded report of “an abnormal radio-active contamination" in the Northern Pacific that greatly exceeded normal levels in the atmosphere. While uncertain as to the cause, the DCI’s first hypothesis was “An atomic explosion on the continent of Asia.” This proved to be accurate – it was the first Soviet test of a nuclear device.
Moscow’s success in building a nuclear bomb was a monumental development made all the more alarming for U.S. strategists by the fact that it occurred one-to-four years sooner than analysts had expected. The White House chose to preempt possible Kremlin triumphalism by announcing the finding to the world on 23 September 1949, a move that evidently came as a shock to the Soviets who had no idea the U.S. had the capability to isolate and identify the signs of a nuclear blast.
Hillenkoetter’s memo, never before published, is at the core of a new posting today by the National Security Archive offering previously classified information and context surrounding the U.S. discovery of the landmark Soviet test. The documents are an update to an earlier Archive compilation and focus on the state of U.S. intelligence about the Soviet nuclear program before and after the test. They help address lingering questions about the unexpected abilities of U.S. nuclear detection technology but also about the disturbing failure to predict the Soviet atomic breakthrough more accurately.
Seventy years ago, on 9 September 1949, Director of Central Intelligence Admiral Roscoe Hillenkoetter handed to President Harry Truman a report that “samples of air masses” collected in the Northern Pacific included evidence of “abnormal radioactive contamination.” According to the report, published for the first time today by the National Security Archive, the intelligence community was not sure whether the contamination was evidence of a Soviet nuclear test or a nuclear accident or something else altogether, but by 21 September it advised Truman that the Soviet Union had staged a nuclear test. Two days later, on 23 September 1949, Truman made headlines with an announcement that the Soviet Union had tested a nuclear device several weeks earlier.
The White House did not explain how the United States had detected the test, which had occurred on 29 August 1949 at Semipalatinsk, in northeastern Kazakhstan. What made the detection possible was that an Air Weather Service plane controlled by the secret U.S. Air Force organization, Air Force Office of Atomic Energy/1 [AFOAT/1], had collected radiological debris produced by the test and that an Air Force contractor confirmed that the material was from an atomic test.
Today’s publication on the detection of “Joe I”, as U.S. intelligence analysts dubbed it, is an update of a National Security Archive posting published ten years ago. That posting drew on previously unpublished declassified material, documenting how the U.S. Air Force and other organizations collaborated to detect a nuclear event that intelligence analysts had not expected for another year or longer. This update includes recently declassified information on the intelligence picture prior to and after Joe 1, including:
- An intelligence report from 1948 on East German production of calcium metal of such high purity that intelligence analysts believed “beyond any shadow of a doubt” that it was “intended for an atomic energy project.” Calcium metal helped produce the uranium reactor fuel that generated plutonium for Moscow’s first bomb.
- A State Department memorandum from July 1949 reporting the existence of “evidence indicating that a chemical extraction plant [with] the earmarks of a plutonium extraction plant has been completed in the USSR,” but no evidence of a nuclear reactor.
- A CIA report from 1957 on the role of German scientists at a Soviet factory that produced uranium metal (used for reactor fuel) of sufficient purity that they “may have advanced the Soviet atomic energy program by about 6 months.”
Detecting Joe 1
The White House announcement on 23 September may have stunned Stalin and the Soviet Politburo; they did not know that the U.S. had a surveillance system geared to detect the tell-tale signs of nuclear activities and they wanted to avoid giving Washington an incentive to accelerate its own nuclear weapons activities. The Soviet test was also a jolt to U.S. intelligence analysts who had estimated that Moscow was unlikely to have the bomb before mid-1953, although they had deemed mid-1950 as a possibility. A few weeks after the test, CIA Director Roscoe Hillenkoetter argued that "I don't think we were taken by surprise" because of an error of only a "few months," but not all of his Congressional overseers accepted that.
How did the Truman administration discover Moscow’s secret? Why had U.S. intelligence been so mistaken?
A few days after the Soviet test, on 3 September 1949, a WB-29 ["W" for weather reconnaissance] operated by the Air Force's Weather Service undertook a routine flight from Misawa Air Force Base (Japan) to Eilson Air Force Base (Alaska) on behalf of the secretive Air Force Office of Atomic Energy-1 [AFOAT-1] [later renamed the Air Force Technical Applications Center, or AFTAC]. The plane carried special filters designed to pick up the radiological debris that an atmospheric atomic test would inevitably create. So far none of the flights in the Northern Pacific had picked up such debris, but after this flight returned to Eilson and a huge Geiger counter checked the filters, the technicians detected radioactive traces. This was the 112th alert of the Atomic Energy Detection System (the previous 111 had been caused by natural occurrences, such as earthquakes).
After a complex chain of events, involving additional flights to collect more air samples, consultations among U.S. government scientists, consultants, and contractors, including radiological analysis by the AFOAT/1 contractor, Tracerlab, and consultations with the British government, the U.S. intelligence community concluded that Moscow had indeed conducted a nuclear test. The test data was codenamed “Vermont.” On 23 September 1949, the White House announced that "We have evidence that within recent weeks an atomic explosion occurred in the U.S.S.R."
That the U.S. government had a system for spotting overseas nuclear activities was a deep secret. During and after World War II, the possibility of detecting radioactive particles and emissions (as well as seismic and acoustic signals) became the subject of protracted research and development work, including the collection of radioactive samples from U.S. atomic tests. In September 1947, Army Chief of Staff Dwight D. Eisenhower assigned the Army Air Force, not yet an independent service, with responsibility for establishing an Atomic Energy Detection System (AEDS). Later that year, the Air Force created what would later become known as AFOAT-1, with responsibility for the surveillance program. AFOAT/1 began to operate an "Interim Surveillance Research Net" that was functional by the spring of 1949. A more comprehensive surveillance system integrating radiochemical, seismic, acoustic, and other methods was not yet in place.
Atomic Energy Commissioner Lewis Strauss sought detection capabilities to avoid an "atomic Pearl Harbor," but U.S. intelligence analysts did not see a Soviet test as a near-term likelihood. Thus, estimates during the years before Joe-1 projected mid-1953 as "the most probable date," although conceding that mid-1950 was also possible. No one in U.S. intelligence realized how quickly the Soviets were moving ahead, or that intelligence gathered by Soviet spies in the U.S. and the United Kingdom would save Moscow a year or two in building its own bomb.
Tight security measures in the Soviet Union made it difficult to produce accurate estimates, but British and U.S. intelligence had collected information that had implications not fully considered by analysts Especially relevant was intelligence on the production in an East German factory of metallic calcium, integral for the production of the uranium metal used to fuel Soviet reactors. Apparently, no one in the intelligence establishment asked why so much metallic calcium was being produced, although it was at levels that suggested that the Soviets could be producing significant quantities of reactor fuel. One of the major analytic units, CIA’s Office of Research and Estimates (ORE), was so disengaged from scientific intelligence that several weeks after the detection of the Soviet test and three days before the White House announcement it produced a paper repeating the estimate of mid-1953 "as the most probable date."
The US Announcement
Once senior scientific advisers confirmed AFOAT/1’s findings, a U.S. announcement was by no means automatic. President Truman was not entirely convinced that a test had taken place and top officials debated whether to announce, with some (AEC Chairman David Lilienthal) arguing that the public had a right to know, while others (Secretary of State Acheson) were more reluctant. Moreover, another important announcement was pending – devaluation of the British pound, and Truman thought two shocks were too many. Yet, he feared that the information would leak (hundreds of U.S. government officials were already in the know), and concluded that an official U.S. announcement was better than a Soviet one.
After Truman’s press secretary handed out the mimeographed announcement, no further information about the discovery was made available, even the estimated date of the test. The U.S. government kept the details secret, although that did not stop informed speculation by journalists and academics about how the test was detected, with some correctly deducing that the U.S. had used radiological analysis. Senator Edwin Johnson (D-CO) inadvertently released an important clue when, during a television interview, he said that the Soviet bomb contained "plutonium," indicating that the United States had acquired traces of the device that it could analyze.
It took years before the fuller story became publicly available. Doyle Northrup, one of the leading officials at AFOAT-1/AFTAC, wrote several narratives that were eventually declassified (with excisions). It was not until the 1990s, however, that two anthropologists at Brandeis University, Charles A. Ziegler and David Jacobson, pieced together the declassified archival record to produce an authoritative and accomplished account of the early history of AFOAT-1 and the detection of Joe-1: Spying Without Spies: Origin of America's Secret Nuclear Intelligence Surveillance System (Praeger, 1995).
The discovery that the United States had lost its nuclear monopoly created alarm about falling behind Moscow and a resolve to stay ahead. Among the measures that reinforced a spiraling nuclear competition were Truman’s decision to approve a Joint Chiefs of Staff proposal to expand fissile material production and his 31 January decision to authorize a thermonuclear weapons program. Moreover, the Soviet test gave impetus to a major policy report, NSC 68 (14 April 1950) calling for massive military spending to offset the political and military impact of Stalin's bomb. 
Stalin may have hoped that secrecy could prevent such U.S. reactions or even a war. Indeed, when the Soviets made a counter-statement on 25 September, they did not acknowledge a weapons test, claiming (preposterously) that the U.S. must have detected “blasting” caused by construction work. Moscow also tried to put a damper on U.S. preventive action by suggesting that it had possessed the bomb since 1947. In any event, the Soviet Union's entrance into the nuclear club may have had a direct impact of an entirely unexpected kind – emboldening Stalin to support Kim Il-sung's plan for a North Korean invasion of the South. As Evgueni Bajanov put it, when Stalin approved Kim's proposal, he was "more confident of the Communist bloc's strength."
Notwithstanding all of the significant declassifications, a complete picture of the role of U.S. intelligence in the events of September 1949 is not yet possible. The part played by AFOAT/1 in detecting the test is well documented, but more needs to be learned about the role of the CIA, which played a central part in coordinating intelligence about the test. Moreover, reports that were of the nature of post-mortems on the intelligence failure remain largely unavailable, such as one by the Office of Scientific Intelligence for which only the conclusions have been declassified. Moreover, in response to a National Security Archive request, the CIA recently denied an unspecified number of documents concerning the detection of Joe I.