William Burr: Intelligence and the Detection of the First Soviet Nuclear Test, September 1949

[Dr. William Burr, Senior Analyst, directs the Archive's nuclear history documentation project.]

Sixty years ago this week, on 23 September 1949, President Harry Truman made headlines when he announced that the Soviet Union had secretly tested a nuclear weapon several weeks earlier. Truman did not explain how the United States had detected the test, which had occurred on 29 August 1949 at Semipalatinsk, a site in northeastern Kazakhstan. Using declassified material, much of which has never been published, this briefing book documents how the U.S. Air Force, the Atomic Energy Commission, and U.S. scientific intelligence worked together to detect a nuclear test that intelligence analysts, still unaware of the extent to which the Soviets had penetrated the Manhattan Project, did not expect so soon.

Stalin and the Soviet Politburo were probably stunned by Truman's announcement; they did not know that Washington had a surveillance system for detecting the tell-tale signs of a nuclear test and they wanted secrecy to avoid giving the United States an incentive to accelerate its nuclear weapons activities. (Note 1) Joe-1 (as U.S. intelligence designated it) was also a jolt for U.S. intelligence analysis, which for several years had asserted that the Soviets were unlikely to have the bomb before mid-1953, although mid-1950 was also possible. 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 masters accepted that.

How did the Truman administration discover Moscow’s secret?

Shortly after the Soviet test, on 1 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 a scent, 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 more flights to collect more air samples, consultations among U.S. government scientists, consultants, and contractors, including radiological analysis by Tracerlab and Los Alamos Laboratory, and secret consultations with the British government, the U.S. intelligence community concluded that Moscow had indeed conducted a nuclear test. On 23 September 1949, President Truman announced that "We have evidence that within recent weeks an atomic explosion occurred in the U.S.S.R." (Note 2)

What made the detection of Joe-1 possible in the first place was a series of decisions that began in 1947. In September of that year, 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) so that physical manifestations of overseas nuclear development activity could be discovered. Later that year, the Air Force created what would later become known as AFOAT-1. During and after World War II, the possibility of detecting radioactive particles and emissions (as well as seismic and acoustic indicators) became the subject of protracted research and development work, which included the collection of radioactive samples following U.S. atomic tests. During 1947-1949, a complex process of review and decision at the Defense Department led to the creation of an "Interim Surveillance Research Net" that was operating routinely by the spring of 1949. A more comprehensive surveillance system integrating radiochemical, seismic, acoustic, and other methods was not yet in place. (Note 3)

While such senior officials as Atomic Energy Commissioner Lewis Strauss sought detection capabilities to avoid an "atomic Pearl Harbor," intelligence analysts did not see a Soviet test as a near-term likelihood. Thus, intelligence estimates produced at the CIA's Office of Research and Estimates (ORE) were significantly off-base, with estimates produced in 1948 and 1949 projecting mid-1953 as "the most probable date," although mid-1950 was possible. Analysts at ORE were so preoccupied with the "big picture" of Soviet intentions that work on the nuclear issue became a marginal part of its effort. Exceptionally tight security measures in the Soviet Union made it difficult to produce accurate estimates of Soviet atomic energy work, but CIA clandestine operators picked up highly relevant information that ORE failed to consider. For example, secretly acquired information provided significant detail on the production in the Soviet zone of Germany of distilled metallic calcium, which is integral to the separation of uranium metal from uranium ore. (Note 4) Nevertheless, ORE analysts were so disengaged from scientific intelligence activity that three days before Truman's announcement they produced a paper repeating the Joint Nuclear Energy Intelligence Committee estimate of mid-1953 "as the most probable date." (Note 5)

The discovery that Washington had lost its nuclear monopoly would have a decisive impact on U.S. diplomacy and military policy; it was one of the stimuli for an interagency report, NSC 68 (14 April 1950), which called for massive military spending to offset the political and military impact of Stalin's bomb. That is exactly what the Soviets had hoped to avoid by keeping their bomb project secret; even when they responded to Truman's announcement, they did not acknowledge that they had tested a weapon and tried to convey "the impression that the Soviet Union had possessed the atomic bomb since 1947." In any event, the Soviet Union's entrance into the nuclear club soon had a direct impact on its policy; it emboldened 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 now more confident of the Communist bloc's strength." (Note 6) ...

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Arnold Shcherban - 9/30/2009

<As Evgueni Bajanov put it, when Stalin approved Kim's proposal, he "was now more confident of the Communist bloc's strength.">
If he was so confident, why didn't he dare to send Soviet Armies battle American ones in Korea, as Chinese did, even when North Korea and Chinese were being decimated in the war?
There is another more straightforward and simple answer why Stalin OKed North Korea's invasion onto South Korean territory: 'cause he had been given strong evidence that South Korean military regime is going to launch a massive strike against North Korea in a matter of weeks.
There were many indications of the latter at the time, which led North Korean leadership to such a conclusion (I can refer whoever is interested to respective detailed Soviet report on the military developments along the 38th parallel right before the start of the war.)
Then, North Korean so called aggression was just a preemptive strike, quite in a manner of Israeli 6-day war of 1967, or many other examples of the preemptive military actions of the most democratic and powerful nations in the world against their political and ideological enemies...

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