Anti Spy Detector: A Cold War Case Study


    The Cold War created some of the most well-known espionage tropes in the public mind. This era encapsulates all that is interesting about intelligence and counterintelligence. Bugging emerged early on as one of the principal ways the United States (US) and Soviet Union (USSR) fought this shadow war. 

    The “Thing” in the Seal of the United States in its Moscow embassy is but one of the dozens of examples of bugging [source]. But how were such devices found?

    1.0: General Overview

    Anti spy detectors are a catchall term for counterintelligence operatives’ devices and methods to find and remove security threats. Countermeasures often emerge only after thoroughly examining the bug in question [source]. To paraphrase Sun Tzu in The Art of War, you must know your enemy in order to defeat him [source]. 

    Naturally, radio equipment became the principal way to find bugs during the Cold War [source]. Commercial devices in the modern era usually incorporate this same technology [source][source]. Listening devices could not store vast amounts of data and were usually inaccessible [source]. This requires radio signals to send the information to listeners [source]. Efficiently countering this required listening in on the data transmitted by these bugs and locating the source of the signal [source].

    In looking at one of the most famous incidents of Cold War bugging, this article seeks to expand on the principles of anti spy detection. It is a complicated process, relying on painstaking sweeps and more than a bit of luck. It also illustrates the cat-and-mouse game of continually developing measures and countermeasures characterising espionage.

    A DFB-1 radio, used for direction finding purposes. It was introduced at the end of WWII.

    2.0: Technical Surveillance Counter-Measures

    The Great Seal bug case study is an example of Technical Surveillance Counter-Measures (TSCM) [source]. The US Department of Defense defines TSCM as “[t]echniques to detect, neutralise, and exploit technical surveillance technologies and hazards that permit the unauthorised access to or removal of information” [source]. In other words, sweeping areas of interest for bugs using an anti spy detector. Examples of equipment used by the groups like the FBI include;

    • Multimeters to measure the electrical characteristics of devices [source],
    • Time-Domain reflectometers to measure characteristics of electrical lines [source],
    • Frequency scanners, similar to those employed by US and Soviet counterintelligence operatives during the Cold War [source],
    • Oscilloscopes to visually represent electrical discharge [source],
    • Spectrum Analysers and Vector Signal Analysers to measure radio frequency magnitude [source],
    • Nonlinear Junction Detectors for finding areas of high radio wave energy [source],
    • And X-Ray and Thermal Imaging devices for obvious reasons [source].

    Many of these are commercially available, typically marketed as “anti spy detectors” [source]. However, as can be seen by the variety of equipment necessary for it, the process of TSCM is time intensive and requires a team of professionals [source]. An industry of security professionals has arisen in response to the demanding work. 

    3.0: The Thing /// A Case Study for Cold War anti spy detection

    A recreation of the Great Seal Bug, located at the International Spy Museum. Original Source:

    In 1945, a group of Soviet children gifted then-US ambassador Averell Harriman with a wood-carved Seal of the United States [source]. Honoured by this, Harriman hung it in the library of his home [source]. However, this was no mere gesture of friendship. The Great Seal Bug, or the Thing as it would come to be known, was a novel design [source]. 

    3.1: Bug Design

    The design of the Great Seal bug differs markedly from its predecessors [source]. 

    3.1.1: Standard Bugs

    Typical Cold War bugs of this era had a power source, an antenna, and a microphone [source]. Power sources were bulky [source]. Understandably, this limited the placement of bugs. Power sources also limited the range at which bugs could transmit data coherently [source]. A CIA bug manufactured in the 1950s had a range of only 100-200 m, meaning listeners had to stay close to pick up traffic [source]. Additionally, the constant transmission of these bugs was a severe issue in maintaining secrecy [source]. Operators tuning their radios could sometimes encounter bug transmissions, which would prompt a bug sweep [source]. 

    The RT-3R is a CIA-designed device from the late 1950s, and exemplifies the standard radio bugs of the early Cold War. Original Image:

    However, these bugs did have substantial utility. The regular production of these devices after more sophisticated technology became available indicates this point [source]. Additionally, these bugs were still difficult to find [source]. A sweep performed at the end of World War II in the US embassy in Moscow discovered 120 devices alone [source]. They continually appeared in unexpected places [source]. While doubtless providing helpful information, the efforts of Soviet spying had substantial psychological effects [source]. Embassy and residence staff had to constantly be mindful of what they said and where they said it [source]. An atmosphere of paranoia and low morale developed in this oppressive environment [source].

    3.1.2: The Great Seal Bug Design

    Because of the deficiencies listed above, the Soviets began efforts in the mid-1940s to construct alternative listening devices [source]. The new design departed from many of the characteristics that describe typical bugs of this time.

    First, it lacked a power source [source]. For this reason, it is a passive receiver, meaning it does not function unless hit with specific radio frequencies [source]. A van would “illuminate” the Great Seal bug from a position near the ambassador’s residence [source].

    Secondly, and related to the previous point, the Thing (as American personnel would call it) was a resonant cavity microphone [source]. It was made up of a copper “membrane” placed in front of a hollow silver-lined space, a capacitor, and an antenna [source]. When people spoke, the membrane would vibrate, and the sound waves would pass through into the cavity [source][source]. If illuminated the capacitor would activate and send audio from the room to the receiver in the van through the antenna [source]. As a result, the Great Seal bug contained no electronics [source].

    These two design choices made detecting the Thing extremely difficult [source]. US officials suspected bugs as far back as 1945 but could not confirm their suspicions until 1952 [source].

    3.2: Finding the Bug

    We can see the problematic nature of finding bugs in the fortunate circumstances that resulted in the Thing’s discovery.

    3.2.1: Seeing the Bug

    In 1951, a British signals officer monitoring Soviet Air Force communications heard the British Air attaché while on routine assignment [source]. Disturbed by this, the British sent an inspector, but he found no devices on his sweep [source]. However, he discovered strong radio signals in the area [source]. The British concluded the Soviets were likely pursuing alternative bugging designs [source]. The UK most likely shared this with the US intelligence community because of the intelligence agreements between the powers at the time [source]. Rumours seem to confirm this point [source].

    Before long, US personnel monitoring radios began overhearing conversations of their own [source]. These originated from the ambassador’s library in his residence. Once again, a sweep by counterintelligence agents turned up nothing. The issue resumed in early 1952 with the arrival of George Kennan as ambassador to the Soviet Union [source]. As the author of the “Long Telegram”, which introduced the US to the concept of containment, he was well-versed in Soviet practices [source]. Moving provided the Soviets with ample opportunities to bug the residence, so Kennan ordered regular sweeps [source]. Yet again, these turned up nothing, but the Americans were confident a device existed in the library [source].

    The Great Seal can be seen to the left of the image. It was prominently placed in the library of the American Ambassadors’ Residence. Original Source:

    3.2.2: Finding the Bug

    In September 1952, the US conducted a more extensive search [source]. Joseph Bezjian, a first US sweep team member, returned as a “guest” to evade suspicion [source]. Kennan read a document deemed safe for interception while Bezjian swept the library with a “Schmidt Kit”, an anti spy detector [source][source]. The Schmidt Kit was a device to listen in on communications from a radio or telephone [source]. It was a crystal video receiver “consisting of an antenna, a detector, and a video amplifier” [source]. . Fitted into a briefcase, it was capable of only limited frequencies [source][source]. Still, it was man-portable and easy to sneak into the residence without issue [source][source]. The Soviets took the bait, and on 10 September 1952, the Great Seal was identified as the source for the transmissions [source]. Subsequently, Kennan sent it to Washington, DC, for further analysis [source].

    4.0: Countermeasures

    The US kept the discovery of the Great Seal bug secret until the 1960s [source]. However, the US immediately took steps to counter these devices [source]. By 3 October 1952, a joint investigation team developed a working anti spy detector prototype [source]. This device was made up of:

    • Three transmitters covering the 65-3000 megahertz range [source],
    • A tone generator to incite Soviet illumination of the bug [source],
    • And a specially developed receiver to interpret the radio waves and render them usable [source].

    Such a countermeasure was time-consuming to employ [source]. Moreover, it was expensive; the production of the receivers, the responsibility of the Atomic Energy Commission, was slow due to production-run and pricing issues [source]. Indeed, by 1953, the FBI had yet to obtain any [source]. 

    Osobnjak 8, a Soviet countermeasure to Western resonant cavity microphones developed in the 80s. Original Source:

    Eventually, the Soviets realised that Western employment of passive resonant cavity microphones was only a matter of time [source]. Indeed, by 1956 the CIA had developed its own device, the EASYCHAIR, which successfully bugged the Russian Embassy in the Hague in 1958 [source]. Soviet countermeasures followed in the steps of the Americans [source]. These largely centred around creating anti spy detectors able to identify radio frequency strength, an indicator of a nearby passive bug [source]. Later countermeasures included direction-finding equipment, allowing operators to find the physical location of a bug [source].

    5.0: Conclusion

    The Great Seal bug is a remarkable showcase of early Cold War espionage. The novel technology allowed the Soviet Union to eavesdrop on seven years of conversations held in the Ambassadors library, granting them a treasure trove of information [source]. It also showcases the espionage cat-and-mouse game, with measures and countermeasures developed in an ever-revolving fashion. Lastly, it displays the arduous task that is TSCM and the need in the intelligence world to be constantly vigilant and aware. 

    Maxwell Goldstein
    Maxwell Goldstein
    Maxwell is a Junior Intelligence Analyst and student pursuing an international master's degree through the Erasmus Mundus IMSISS programme. His areas of focus are aerospace, technology, and the Indo-Pacific.

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