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CIA covert listening devices

EASYCHAIR, or Easy Chair, or EC, was the codename of a super secret research project, initiated by the US Central Intelligence Agency (CIA), aiming to develop covert listening devices (bugs) based on the principle of the Resonant Cavity Microphone, also known as The Great Seal Bug or The Thing, that was found in 1952 in the study of the US ambassador's residency in Moscow. The secret research took place in the Netherlands at the Dutch Radar Laboratory (NRP) in Noordwijk.
Post-Easy Chair equipment on this website
1500 MHz covert transmitter with noise-based speech masking High-performance covert antenna 1500 MHz antenna for Listening Post (1500 MHz) Fixed 1500 MHz antenna for target (bug) Path loss survey system Universal Radio Transmitter (part of URS-1) 312-320 MHz Universal Radio Receiver (part of URS-1) 312-320 MHz

On 4 August 1945, the Vladimir Lenin All-Union Pioneer Organisation presented a hand-carved replica of the Great Seal of the United States to US Ambassador Averell Harriman, as a gesture of friendship to the USSR's World War Two ally. Unknown to to Harriman, the carving contained an hitherto unknown type of listening device, that became known as a resonant cavity microphone. The carving was hung in the Ambassador's study and provided the Soviets with the best possible intelligence for nearly seven years, before it was accidently discovered during a sweep operation.
Immediately after the discovery of the device in September 1952, it was handed over to the FBI [1], where it was thoroughly investigated at their Technical Laboratory. After the first preliminary findings on 23 September, a full technical report was issued by the FBI on 1 December 1952 [2].

During the FBI investigation, the progress was constantly reported to a special commission, as directed by the President, consisting of the IIC, the ICIS and the CIA. Based on this information, the CIA built a number of functional replicas of The Thing for internal and external research [8].
At present we do not have a proper image of an EASY CHAIR device

It is often thought that the American's had no idea how the device worked and that they turned in desperation to the UK for help, where part-time MI5 consultant Peter Wright solved the problem for them in about 10 weeks [3]. Although it is probably correct that Wright investigated the device and was able to build a British replica of it, codenamed SATYR, he was certainly not the only one to be involved. Unknown to Wright, and probably also to MI5, the CIA started a secret research project under the codename EASYCHAIR. In his book Molehunt [4], David Wise writes about this:
    Great Seal was given the code name EASY CHAIR by the CIA. The actual
    research was being performed in a laboratory in the Netherlands in two
    supersecret projects code-named MARK 2 and MARK 3.
A single paragraph in a single book referring to an unnamed Dutch laboratory was for many years the only indication that the Netherlands had been involved in the development of an equivalent of the Russian bug. In September 2015, the Dutch online magazine De Correspondent revealed the name of the Dutch laboratory, in the article Operatie Leunstoel (Eng: Operation Easy Chair) [5].

 More about The Great Seal Bug

NRP   Dutch Radar Laboratory
Nederlands Radar Proefstation

In the early 1950s, shortly after EASYCHAIR research had been launched, the CIA contacted the Dutch Security Agency (BVD), in the hope that they could consult engineers and scientists of a high-tech company, such as the Philips Research Laboratory in Eindhoven. As it turned out, the Philips Corporation was not interested in 'small low-profile research', and declined, after which the director of the BVD, Louis Einthoven [6], consulted his wartime friend JMPA (Joop) van Dijk.
Einthoven 1 and van Dijk, had both been active in the resistance during WWII, and van Dijk had just established the Dutch Radar Laboratory (NRP), in an attempt to bring the country up to speed with the latest radar technology. Being specialised in UHF and SHF technology, and resonant cavities in particular, the NRP was ideally suited for the job.

During the course of 1954 2 the NRP was visited by people from the CIA, who told them that a mysterious bug had been found in a chair, hence the project name EASY CHAIR, or EC. The visit resulted in a research contract between the NRP and the CIA that would last for several decades.

At the time, the NRP was housed in a large villa, named Wave Guide, right at the Dutch coast in Noordwijk. It was the NRP headquarters for many years and is shown in the image on the right.

Involved in the EASY CHAIR research were NRP engineers Jan-Albert Bijvoet, Gerhard Prins and Joop van Dijk himself. Bijvoet would later be replaced by Thijs Hoekstra and At Admiraal. In the early years, the work was carried out in the evenings, after normal office hours, when the rest of the workforce had left, but that changed after the first successful product was released in 1956.

In the following years, many EASY CHAIR (EC) devices were built for the CIA and also some for the Dutch Security Service, the BVD, although the latter had to obtain the CIA's permission for each operation in which an EC device was involved. The NRP was even involved in planting some of the listening devices, such as the bugging of the Russian Embassy in 1958 and the Chinese Embassy.

Despite the close cooperation with the CIA, it wasn't until 1960 that the NRP learned that the original resonant cavity mircophone was not found an an easy chair, but inside a wooden carving of The Greal Seal of the United States that they had received as a gift from the Russians in 1945.

The cooperation between the NRP and the CIA, that started in 1954, lasted until at least the early 1990s, during which time a wealth of transmitters, receivers and test equipment was supplied to the CIA. According to Prins [7], the CIA orders were responsible for half the company's turnover (and sometimes even more) for many years. This did not go unnoticed to the rest of the NRP and CHL 3 personnel, who believed that the NRP just made test equipment for the US Government [9].

The Dutch Intelligence Agency BVD was only partially aware of the level of cooperation between the NRP and the CIA. Much of the work for the CIA happened outside the view of the BVD. That said, new NRP personnel had to be screened by the BVD for many years, which implies that the BVD was not completely in the dark. Besides, the NRP had an armed guard on site and were watched during the night by the Dutch Army.

 More about the NRP
  1. During his wartime resistance work, Louis Einthoven was known as The Colonel.
  2. In a letter to his heirs [7], Gerhard Prins states that the first contact with the CIA was in 1954, but in the article in De Correspondent [5], the authors have changed this to 1952. Based on documents that are in our possession, we believe the former (1954) to be correct.
  3. CHL = Christiaan Huygens Laboratory, a subsidary of the NRP, located in an adjacent building.

CIA research on EASYCHAIR
The first contact between the CIA and the NRP dates back to 1954 (see above), but before the work on EASYCHAIR could start, the company, its directors and all personnel involved had to be screened by the BVD, a the request of the CIA. Once approved, the work could commence.
Shortly after The Thing had been discovered in Moscow, the CIA is briefed on the matter by the Federal Bureau of Investigation (FBI). During the investigation, the CIA is kept informed of the progress via a special IIC-ICIS-CIA commission (SC), as directed by the US President (POTUS).

Based on this information, the CIA started its own research project with the aim to develop listening devices based on the same principle. The program was codenamed EASY CHAIR [4].

For internal and external research, the CIA had built a number of resonant cavity micro­phones that were very similar to The Thing, albeit with limited success. They were accompanied by a technical discription of their operation [8]. A cross section of the device is shown on the right.

It is doubtful whether the CIA had a good and full understanding of the device's operation, as their test results do not reflect the experiences of the FBI, the NRL and the SCEL, all of which built functional replicas in 1952 and reported that the device had excellent audio sensitivity.

Furthermore, the CIA device worked at a much lower frequency (1002 MHz) than the original Russian one (1700 MHz). Nevertheless they did some serious research, and saw room for future improvements. They gave the device a calibrated adjustable tuning post and replaced the nickel membrane by a mylar 1 one, upon which a thin aluminium layer had been evaporated [8].

Interestingly, the CIA has specified the antenna length in the drawing above at λ/2, whereas according to the preliminary findings of the FBI it was 1½λ long. This clearly indicates that the CIA had diverted from the original design and from the later replicas built by the FBI and the SCEL. As part of the project, a CIA replica was delivered to the NRP in July 1955, along with the report [8].

 Read the complete uncensored CIA report
  1. Mylar, or BoPET, is a very strong and stable thin polyester film.   Wikipedia

NRP research on EASYCHAIR
Based on the information supplied by the CIA [8], the NRP was unable to create a reliable replica of The Thing in 1955, so they concentrated on their own research. After initial experiments with 10 GHz (3 cm) signals had failed due to the high damping of the walls of a building, an input frequency of 375 MHz was chosen. With just 40W of RF power, it appeared to be possible to use the bug in any room of the three-story building. It marked the start of a successful relationship with the CIA and the development of a range of covert listening devices and matching receivers.
Easy Chair Mark I
In the early days, the engineers at the NRP had to work on EASYCHAIR in their own time, after office hours. Their first success came in 1956. Using the diode and transistor technology that had just become available, they were able to build their first Passive Element 1 , or PE. A strong UHF signal, directed at the PE, was first rectified and then used to feed a small 3-stage microphone amplifier, the load of which caused the re-emitted signal to be Amplitude Modulated (AM).

Block diagram of the Easy Chair Mark 1

In October 1956, Joop van Dijk and Gerhard Prins of the NRP travelled to the US, to demonstrate their solution to the Contracting Group of the CIA. The trip payed off, as it resulted in an order for 6 portable units that were identified as Easy Chair Mark I, or EC Mk I. It was the start of a successful relationship with the CIA that would last for more than 30 years.
  1. Stricktly speaking, the device no longer was a Passive Element in the same sense as The Thing, when active components like diodes and transistors were added. However, as it didn't need its own local power source, they kept referring to it as a Passive Element, or PE.

Later work
From this point onwards, the work was carried out during normal office hours in a new secured laboratory, with the evenings only needed for field tests. After a visit from CIA head Allan Dulles 1 in 1957, the green light was given for the development of the EC Mk II, III, IV and V, the last of which modulated the microphone signal onto a frequency-modulated subcarrier, so that multiple bugs could be received at the listening post simultaneously. The bugs were activated by a 500W transmitter in combination with a 14dB corner reflector antenna, resulting in an ERP 2 of 10kW.
Approx. fifteen years after starting to work for the CIA, around 1970, the NRP was able to construct a reliably working replica of The Thing, but this never got beyond the prototype stage. By that time, interest in this type of device had dropped and the CIA was no longer interested.

Although the early (passive) EASY CHAIR devices worked very well, they had a number of serious limitations, such as a short operational range, the rather large listening post that was needed, and the very strong RF activation signal that sooner or later would be noticed by the target.
SRT-107 bug, developed around 1974.

The NRP therefore started its own research in the area of Active Target Elements (ATE) which were powered by batteries, the mains network or a telephone line. It was important to keep the power consumption to a minimum, have the ability to turn the device ON and OFF remotely, and to mask the audio modulation, so that the devices could not be picked up with a normal receiver [7].
  1. The presence of CIA head Allan Dulles at the demonstration in Wassenaar (Netherlands) in October 1957, is only mentioned in a letter in the estate of Gerhard Prins [7] and is not supported by any other public historical document. However, as he (Prins) and company director Joop van Dijk later both received a personally signed copy of Dulles' book The Craft of Intelligence, this might actually have been the case.
  2. ERP = Effectively Radiated Power.

Bugging the Russian Embassy in The Hague
Covert CIA-BVD-NRP operation

In 1958, in a joint operation of the CIA, the BVD and the NRP, an attempt was made to bug the Russian Embassy in The Hague (Netherlands), who had just ordered new furniture for the ambassador's office. One of the PE devices 1 was hidden by the BVD inside one of the legs of a desk, and the attic of a nearby school was used to install the powerful activation transmitter [7].

As the PE could not be activated from the school's attic, it was thought that perhaps it was broken or discovered by the Russians. In order to verify this, an old lorry was parked in front of the embassy, pretending to have motor problems. Inside the lorry, that was driven by a BVD agent codenamed 'Herman', were NRP-engineer Thijs Hoekstra and an undisclosed CIA operative. They were using one of the old 40W transmitters from the earlier experiments. To their great joy, the PE worked and the first thing they heard was the ambassador's 'big belly laugh'.

New antennas were installed at the school's attic, raising the gain by another 20dB, and the decoupling between transmitter and receiver was further improved. Finally they were able to activate the PE from this location and over the next 6 months the bug provided great intelligence.
  1. PE (Passive Element) was the internal NRP name for the CIA's Easy Chair (EC) device.

Bugging the Russian Embassy in Washington
In 1987, the American government accused the Soviets of bugging their embassy in Moscow. The Russians replied with a press conference on 10 April 1987, saying that the American claims were unfounded, but that instead their embassy in Washington had been bugged by the Americans.

The leftmost image above shows the Russian press conference. Behind the table, various panels have been installed with photographs and real samples of the equipment that had been found. At the bottom of the second panel from the left, a group of four devices is visible (in the red circle). The rightmost image shows the same items as they appeared on television that evening.

As far as we can tell, this is one of the later Active Target Elements (ATEs) of the CIA, built by the NRP. From left to right we see the audio coder, the transmitter, the battery and the antenna. The antenna is a typical SRN-85 which was widely used by the CIA. The shiny cylinder (2nd from the right) contains four Mercury battery cells which provided enough energy for many hours of use.

It is likely that the leftmost unit was the audio coder, which was used to mask the modulation of the transmitted RF signal. In later CIA bugs, such as the SRT-107, coder and transmitter were mounted in a single cylinder. It is also possible however, that it contained a receiver which was used to turn the transmitter ON and OFF at will, resulting in a much longer operational life.

Known Easy Chair products
  • Coaxial antennas
  • Receive antenna for URS-1
  • Listening post antenna (1500 MHz)
  • Target antenna (1500 MHz)
  • Covert 1500 MHz transmitter (bug) with audio masking
  • Uniform reference receiver (312 MHz)
  • Uniform reference system (in Samsonite briefcase)
  • Uniform reference transmitter (312 MHz)
AM   Amplitude Modulation

ATE   Active Target Element
Active bugging device that has its own power source, can be controlled remotely and has full masking of its audio signal.

BVD   Binnenlandse Veiligheidsdienst
Dutch internal security service, later renamed to AIVD.  More

CIA   Central Intelligence Agency
United Status intelligence agency.  More

CIA codename for the super-secret project to develop covert listening devices based on the principle of the Russian resonant cavity microphone, also known as The Thing. The name EASY CHAIR is also written as EASYCHAIR.

ERP   Effectively Radiated Power

FBI   Federal Bureau of Investigation
United States federal law enforcement agency, tasked with the investigation of federal (cyber) crime, corruption, terrorism and counterintelligence.  More

FM   Frequency Modulation

NRL   Naval Research Laboratory
Technical research laboratory of the US Navy.

NRP   Nederlands Radar Proefstation
Dutch Radar Laboratory, at the time located in Noordwijk (Netherlands).  More

MI5   Military Intelligence 5
British internal intelligence agency.  More

PE   Passive Element
NRP name for derrivatives of the resonant cavity microphone.

POTUS   President of The United States

SC   Special Commission
Special intelligence commission established by the US President, consisting of the IIC, ICIS and CIA, to share research information about the Russian resonant cavity microphone (The Thing).

SCEL   Signal Corps Engineering Laboratories
Technical engineering laboratory of the US Army Signal Corps, based at Fort Monmouth (New Jersey, USA).

SHF   Super High Frequency
Common expression for frequencies of 800 MHz and above.

UHF   Ultra High Frequency
Common expression for frequencies in the range 200 - 800 MHz.

WWII   World War II
Also known as World War 2, or the Second World War.

  1. I.W. Conrad to Mr. Harbo, Results of laboratory examination
    Internal FBI memorandum. 23 September 1952. 1

  2. Director FBI to POTUS, Release of FBI report on Russian microphone
    Official letter, via Matt Connelly, to the US President. 4 December 1952. 1

  3. Peter Wright, Spycatcher
    ISBN 0-440-29504-1. 1987-1988.

  4. David Wise, Molehunt
    ISBN 978-0394585147. 10 March 1992.

  5. Maurits Martijn & Cees Wiebes, Operation Easy Chair
    De Correspondent. 24 September 2015.

  6. Wikipedia, Louis Einthoven
    Dutch. Retrieved October 2015.

  7. Gerhard Prins, Letter to his heirs
    Date unknown, but probably written shortly before his death in April 1993.
    Vertrouwelijk (confidential). Published by [5].

  8. CIA Contracting Group, Report on Research on EASYCHAIR
    14 July 1955. Classification status unknown. Not marked as secret.

  9. Nederlands Radar Proefstation 40 Jaar / 1947-1987
    July 1987. Chapter 'Amerikaanse zaken' (American affairs).

  1. Released by the FBI under the Freedom of Information Act (FIOA) on 11 May 2014 (FOI/PA# 1173422-1).

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Crypto Museum. Created: Tuesday 12 January 2016. Last changed: Tuesday, 10 January 2017 - 08:47 CET.
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