35+ Years of Freedom of Information Action

Detection of the First Soviet Nuclear Test, September 1949

 Photo from Peter Curan’s film "Trinity and Beyond: The Atomic Bomb Movie

Joe-1, 29 August 1949. Photo from Peter Kuran’s film "Trinity and Beyond: The Atomic Bomb Movie," as displayed on nuclearweaponsarchive.org, and used with permission of Peter Kuran.

Published: Sep 9, 2019
Briefing Book #684

Edited by William Burr

For more information, contact:
202-994-7000 or nsarchiv@gwu.edu

Newly Declassified Documents Trace Beginnings of Superpower Nuclear Arms Race

Soviet Atomic Project Posed Major Challenge to U.S. Intelligence

Records Expand Knowledge of the Role of German Scientists in Advancing the Soviet Nuclear Program

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.[1] 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.[2] 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."[3]

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.[4]

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.[5]

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.[6] 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."[7]


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.[8]

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.[9]

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).[10]



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. [11]

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."[12]

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.


Read the Documents

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Document 26
Central Intelligence Agency, “Review of the World Situation,” 19 October 1949, CIA 10-49, Secret

A brief analysis of the Soviet test in this CIA publication found that the Soviets had gained a political advantage. Despite the test, it did not fundamentally change the U.S.’s military-security position; the “superior US stockpile” remained a “significant” advantage. To identify a prospective military threat, it would be necessary to “determine the time at which the rising curve of a Soviet stockpile will reach a point at which it can be considered operationally effective.” The fact that the Soviets had an “ability to stockpile” was another matter because it raised “psychological and political imponderables.” Moscow’s access to atomic technology “permits [it] to exert psychological and political pressures in Western Europe.” While the Soviets had not yet exerted such pressure, and there was no way to gauge European reactions to pressure, “it is certain that the USSR has an enhanced ‘cold war’ capability.”

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Document 27
"Estimate of the Effects of Soviet Possession of the Atomic Bomb upon the Security of the United States and Upon the Probabilities of Direct Soviet Military Action," ORE 91-41, 6 April 1950. Top Secret

To deal with the strategic issues raised by the Soviet bomb, the CIA produced a long analysis, focusing not only on Soviet nuclear capabilities but also on Moscow's intentions and the extent to which a nuclear weapons capability increased the risk of U.S.-Soviet conflict. The analysts reached the general conclusion that they saw “no firm basis for an assumption that the USSR presently intends deliberately to use military force to attain a Communist world or further to expand Soviet territory if this involves war with a potentially stronger US.” Even with atomic weapons, Soviet intentions were unlikely to change although “a Soviet capability for effective direct attack upon the continental US must be considered to increase the danger that the USSR might resort to military action to attain its objectives.” Dissents by the intelligence organizations of the State Department, the Navy, the Army, and the Air Force indicated profound misgivings about the ORE estimate of Soviet intentions. For example, the State Department dissented from the conclusion that “except under extreme and apparently unlikely circumstances, the USSR will not deliberately employ military force in its struggle against the US.”

Part VI: The German Factor: Future Findings

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Document 28
Central Intelligence Agency, Office of Scientific Intelligence, “Contributions of German Scientists to the Atomic Energy Program – Agudzeri,” Research Supplement to Scientific Intelligence Report CIA/SI 2-57, CIA/SI 2-SE III-57, 15 April 1957, Secret, Excised Copy
Source: Mandatory declassification review request to CIA

While U.S. and British intelligence were well aware that captured German scientists were playing multiple roles in the Soviet nuclear program, they did not have the details until they could interview the scientists when they began to return during the 1950s (Operation DRAGON). Some of the interview-based reports have already been declassified and published in a National Security Archive posting. This report, along with the next two documents, add to the knowledge base of the work on the German scientists, although they have to be checked against other sources.[20]

According to the report, German scientists at the Agudzeri Institute successfully developed a mass spectrometer which is essential to measure the results of uranium isotope separation activities. Another success was Heinz Barwich’s contribution to the gaseous diffusion program, including theoretical work on cascade theory, for which he was awarded a Stalin Prize. By contrast, Nobel Prize winner Gustav Hertz’s effort to develop an industrial-scale method to separate uranium isotopes was a failure.

At the end of this document, like the two that follow, are excised pages that probably list the German scientists and technicians who had been interviewed.

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Document 29
Central Intelligence Agency, Office of Scientific Intelligence, “Contributions of German Scientists to the Atomic Energy Program – Sinop,” Research Supplement to Scientific Intelligence Report CIA/SI 2-57, CIA/SI 2-SE I-57, 15 April 1957, Secret, Excised Copy
Source: Mandatory declassification review request to CIA

The Sinop Institute, like Agudzeri, focused on isotope separation, but with greater success, according to the CIA. The leading figure was Baron Manfred Von Ardenne, whom some of the Germans saw as a “charlatan,” although with very good organizational skills. Research on electromagnetic separation of uranium isotopes began at Sinop but was eventually given low priority because the gaseous diffusion method proved more successful. In that respect, “The contributions of [Peter Adolph] Thiessen and of his group … at Sinop must be ranked high among the German contributions to the Soviet atomic energy program,” largely because of their development of the barriers used in gaseous diffusion plants.[21]

Another major project at Sinop was the ultracentrifuge research directed by Max Steenbeck. The Germans may have convinced the Soviets that the gas centrifuge was an “ideal” method for isotope separation compared to gaseous diffusion, but technical problems were difficult to solve: the high speeds required (100,000 RPM) caused the rotors and bearings to fail.

In 1953, key personnel in the Steenbeck group were sent to Leningrad for further R&D work. Gernot Zippe, identified as the head of Ultracentrifuge Team I, later became an important source on the progress of the Soviet gas centrifuge program. The drafters of this report did not have access to Zippe and the Steenbeck group, who did not return to the West until late 1956. Consequently, the report’s findings were rather downbeat: the “Steenbeck group probably made no substantial contribution to the overall success of the Soviet atomic energy program other than to vigorously investigate one possible means of isotope separation.”

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Document 30
Central Intelligence Agency, Office of Scientific Intelligence, “Contributions of German Scientists to the Atomic Energy Program – Elektrostal,” Research Supplement to Scientific Intelligence Report CIA/SI 2-57, CIA/SI 2-SE IV-57, 15 July1957, Secret, Excised Copy
Source: Mandatory declassification review request to CIA

The German scientists at Elekrostal led by Nikolaus Riehl made a contribution to the Soviet atomic project that CIA analysts believed had saved the Soviets about “six months” of work. Born in Russia, Riehl directed research at the Auer Company, which manufactured uranium metal for the Nazi atomic weapons project. According to this report, two key Soviets, Iulii Khariton and General A.P. Zaveniagin who were in Berlin after the Nazi collapse made Riehl an offer to produce uranium in a Soviet laboratory.[22] The Soviets gave top priority to the production of “pure uranium metal in sufficient quantity for the operation of reactors producing plutonium.”

At Elektrostal, Riehl’s group tried to reduce uranium oxide to metallic form but the results were not sufficiently pure. They then successfully processed uranium tetrafluoride (UF4) into pure uranium metal. In both instances, the reducing element was the pure calcium produced by the plant at Bitterfeld, East Germany (see document ….). Much of the work was accomplished during 1946-1947, although the scientists “retained much value” for the Soviets. By 1952 all of the German scientists at Elektrostal had been sent to Sukhumi, Georgia, for a period of “forgetfulness” or “quarantine” before returning to Germany in 1955.

A note on page 9 indicates that the CIA’s sources of information on Elektrostal included Nikolaus Riehl, Gunther Wirths, and Karl Heinrich Riewe.

* Thanks to Michael Goodman and the late Jeffrey Richelson for assistance with the first version of this publication. Thanks to Sam Rushay at the Harry S. Truman Library for kindly providing copies of several documents, to Alexander Chang for transcribing George Elsey’s handwritten notes, and to Frank von Hippel (Princeton University) for his wise counsel.




[1]. For the naming of “Joe 1,” see Michael D. Gordin, Red Cloud at Dawn : Truman, Stalin, and the End of the Atomic Monopoly (New York: Farrar, Strauss, and Giroux, 2009). 357, note 3.

[2] . David Holloway, Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939-1956 (New Haven: Yale University Press, 1994), 266-267.

[3]. For the detection the Soviet test, see Jeffrey Richelson, Spying on the Bomb: American Nuclear Intelligence from Nazi Germany to Iran and North Korea (New York: W.W. Norton, 2007), 88-92.

[4] . For details, see Charles A. Ziegler and David Jacobson, Spying Without Spies: Origin of America's Secret Nuclear Intelligence Surveillance System (Praeger, 1995)

[5] . David Holloway, “Barbarossa and the Bomb: Two Cases of Soviet Intelligence in World War II,” Jonathan Haslam and Karina Urbach, eds., Secret Intelligence in the European State System, 1918-1989 (Palo Alto: Stanford University Press, 2013), 62.

[6] . Donald P. Steury, "How the CIA Missed Stalin's Bomb," Studies in Intelligence 49 No. 1 (2005), 19-26, and Richelson, Spying on the Bomb, 92l; Henry Lowenhaupt "Chasing Bitterfeld Calcium," Studies in Intelligence (pdf) Studies in Intelligence 17 (Spring 1973): 21-30.

[7] . Intelligence Memorandum No. 225, "Estimate of Status of Atomic Warfare in the USSR," 20 September 1949, in Michael Warner, editor, The CIA under Harry Truman (Washington, D.C.: History Staff, Center for the Study of Intelligence, 1994), 319.

[8] . For a detailed account, see Gordin, Red Cloud at Dawn, 216-238. For Lilienthal’s role, see Journals of David Lilienthal Volume 2: The Atomic Energy Years (New York: Harper & Row, 1964), 569-572.

[9] . Truman later reprimanded Senator Johnson for the disclosure. "Science: So It Was Plutonium," Time, 5 December 1949

[10] . See also Richelson, Spying on the Bomb, especially 62-104, and Michael S. Goodman, Spying on the Nuclear Bear: Anglo-American Intelligence and the Soviet Bomb (Stanford: Stanford University Press, 2007

[11] . Melvyn P. Leffler, A Preponderance of Power: National Security, the Truman Administration, and the Cold War (Stanford: Stanford University Press, 1992), 325-333, and Gordin, Red Cloud at Dawn, 247-275.

[12] Holloway, Stalin and the Bomb, 266-267; Evgueni Bajanov, "Assessing the Politics of the Korean War, 1949-51," Bulletin of the Cold War International History Project 6/7 (1995): 87; Vladislav Zubok, A Failed Empire: The Soviet Union in the Cold War from Stalin to Khrushchev (Chapel Hill: University of North Carolina Press, 2007), 86 (citing Bajanov). For the Soviet announcement and further discussion, see Gordin, Red Cloud at Dawn, 240-244.

[13] . Ziegler and Jacobson, Spying Without Spies, 210.

[14]. For Bitterfeld in context, see Henry Lowenhaupt, “Chasing Bitterfeld Calcium.”

[15] . For Soviet production of highly pure graphite and the construction of a production reactor near Kyshtym, see Holloway, Stalin and the Bomb, 100-101 and 183-187.

[16] . See also, Ziegler and Jacobson, Spying Without Spies, 210-211; Richelson, Spying on the Bomb, 90

[17]. For the Navy project, see Herbert Friedman, Luther B. Lockhart, and Irving H. Blifford, "Detecting the Soviet Bomb: Joe-1 in a Rain Barrel," Physics Today 49 (November 1996): 38-41.

[18]. Steven Zaloga, The Kremlin's Nuclear Sword: The Rise and Fall of Russia's Strategic Nuclear Force, 1945-2000 (Washington, D.C.: Smithsonian Institution Press, 2002), 10-12

[19] . The Los Alamos findings corresponded to the findings of the AFOAT-1 contractor, Tracerlab. See Ziegler and Jacobson, Spying Without Spies, 187-189, 207.

[20] . Pavel V. Oleynikov’s “German Scientists in the Soviet Atomic Project,” The Nonproliferation Review, 7 (2000), 1-30, provides a valuable account of these developments.

[21]. For more on gaseous diffusion, see Holloway, Stalin and the Bomb, 191-192.

[22] . Ibid., 109-112. See also Oleynikov, “German Scientists,” at 7. During this trip, the Soviets also acquired 300 hundred tons of uranium oxide that the Germans had hidden.