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CIA NRP
CIA covert listening devices
EASYCHAIR – also EASY CHAIR or EC – was the codename of a secret
research program, initiated by the US
Central Intelligence Agency (CIA)
and carried out by the Dutch Radar Laboratory (NRP)
in Noordwijk (Netherlands).
The aim of the project was 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 had been found in 1952
in the library of the US ambassador's residency in Moscow (Russia),
hidden inside a gifted wooden carving of the Great Seal of the United States.
Immediately after the discovery of the Thing the FBI
and NRL started a formal investigation into the operation of the device.
In parallel – separately from the FBI – the CIA started its own
research program — codenamed EASYCHAIR and carried out by the NRP — to see
if this technology could be of use to the CIA. The initial program ran
from 1954 to 1967, but was extended several times.
The relationship between the CIA and the NRP lasted until
the demise of the latter in 1994.
➤ EASYCHAIR history
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EASYCHAIR equipment on this website
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The initial EASYCHAIR research program lasted from 1954 to approx.
1967. After that, the secret research continued under the same
name, but the actual devices were no longer known as EASYCHAIR (EC).
Instead they were identified by CIA-provided designators, like
SRT-107 and SRR-90.
Nevertheless, the later devices produced by the NRP are often named
EASYCHAIR to discriminate them from CIA bugs made by other suppliers.
To avoid confusion, we will call the later devices post-EASYCHAIR
throughout this website.
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Post-EASYCHAIR equipment on this website
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Measurement and test devices
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Complete surveillance systems
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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 II (WWII) ally. Unknown 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 discovered during a staged sweep operation.
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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].
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It is often thought that the Americans 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].
It is probably correct that Wright investigated the device
and was able to build a British replica of it
— codenamed SATYR —
but 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:
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The effort to copy the Soviet bug that had been discovered inside the
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 clue that the Netherlands
had been involved in the development of an equivalent of the
Russian bug.
In September 2015, in the article Operatie Leunstoel
(Operation Easy Chair), the Dutch online magazine
De Correspondent
revealed that it was the Dutch Radar Laboratory [5].
➤ More about The Great Seal Bug
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In late 1952, the CIA contacted the
Dutch Internal Security Agency (BVD, now AIVD),
in the hope that they could appoint engineers and scientists to help with their
investigation. It was thought that the multinational
Philips corporation might be
able to help. On 28 October 1952, little more than one month after the discovery of
the Thing, BVD officer Cees wrote a letter to
Theo Tromp, member of the Philips Board of Directors, in which he reveals an unknown
device (translated):
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From the American side we've been confidentially informed that microphones
with a diameter similar to a Rijksdaalder have been found at various
American diplomatic facilities behind the Iron Curtain.
These microphones contain a battery and are said
to have a range of 10 km. [...]
They were found in easy chairs etc.
Do you think it possible that such devices exist and, if they do,
what their lifespan would be? The Americans are rather upset about this,
as the devices cannot be discovered in the usual manner. They are completely
made of plastic. [...]
During WWII, Tromp had briefly been Minister of Traffic but also was an active
member of the Dutch resistance group Harry. He also had frequent contacts
with two major resistance groups: Ordedienst
en Raad van Verzet (RVV) [10].
It is likely that he was trusted by the director of the BVD, Louis Einthoven,
who who had recruted much of his personnel from the former resistance.
It is unknown who Tromps BVD contact Cees was, but it is
possible, if not likely, that this was Cees van den Heuvel, the head of the
Training and Research section of the BVD, who operated from his office at
the Van Stolkweg in Den Haag. During the war, van den Heuvel was a member of
the resistance group Albrecht; one of the few groups that was never
captured by the Germans [11]. It is likely that the two men knew
each other from their wartime underground work.
There are several issues with the above quoted letter [12]. No battery was
used with this type of listening device, and it is unlikely that it was
entirely made of plastic. Furthermore, a range of 10 km seems unrealistic,
even by today's standards.
It is possible that Cees' contact at the CIA
was not technically knowledgeable or had (deliberately) been misinformed.
What is remarkable though, is that these devices had reportedly
been found in easy chairs (fauteuils), and that it had the diameter of a
Rijksdaalder — a Dutch NLG 2.50 coin with a diameter of 33 or 38 mm.
➤ Read the original letter (in Dutch)
Apparently Tromp had the same reservations about the letter. In his answer
the following day, he challenged the range of 10 km and rightfully remarked
that a battery powered device would last hours instead of days, especially
with the batteries that were available at the time [13]. In reply to the claim
that the device was entirely made of plastic, he suggested the following:
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The message that these devices exist and the addition that they
appear to be completely made of plastic, could indicate that so-called
Germanium triodes are used, also known as 'transistors'.
The transistor had been invented by Bell Labs in 1947,
but by 1952 its development was still in its infacy and was not widely
used in equipment. Tromp suggested that it might even be possible that the
Russians had developed their own version of the transistor, and that they
had used it in this novel device. Unfortunately, all of this was based
on false and incomplete information.
➤ Read the full reply from Tromp
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So far, the above is the only evidence that the BVD spoke with
Philips about the discovery of the device.
It is likely that in the following year, Philips Natuurkundig Laboratorium
(later: Philips Research) was approached,
but it turned out to be a dead end.
Apparently, Philips was not interested
in a follow-up, as it declined a request from BVD director van Einthoven
to further research the secret technology. It is possible that Philips
was too busy rebuilding their business in post-war Netherlands,
or that they were only interested in high-volume consumer products.
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Dutch Radar Laboratory (NRP)
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Nederlands Radar Proefstation
After Philips had declined, the director of the BVD — Louis Einthoven [6] 1 —
decided to consult Joop van Dijk — another wartime resistance friend.
Van Dijk had just established the
Dutch Radar Laboratory (NRP) in Noordwijk
(Netherlands) in an attempt to bring the Netherlands up to speed
with the latest developments in radar technology, with help from people
like Watson-Watt [14].
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The NRP was located right at the Dutch coast, and Noordwijk was
conveniently close to Den Haag (The Hague) were both the BVD and the
American embassy were based. Specialised in radar and UHF/SHF radio
technology, the NRP appreared to be the ideal partner to secretly research
the resonant cavity microphone.
During the course of 1954 2 the NRP was visited by people from the CIA,
who told them that a mysterious bug was found in an easy chair, hence
the project name EASYCHAIR. 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 is shown in the image on the right and was the NRP headquarters for
many years.
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Involved in the EASYCHAIR 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.
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The image on the right shows an Easy Chair Mark I,
that consisted of two modules. It did not need a battery,
as it was powered by a strong RF signal beamed at it
from a nearby listening post.
In the following years, many EASYCHAIR (EC) devices were built for the
CIA and also for the Dutch Internal Security Service (BVD),
although the latter had to obtain the
CIA's permission for each operation that involved an EC device.
The NRP was even involved in planting some of the listening devices,
such as the bugging of the
Russian and Chinese embassies in The Hague.
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Despite the close relationship 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 1994, during which time many transmitters, receivers, bugs
and test devices were developed and supplied to the CIA.
According to Prins in [7], the CIA orders
accounted for half the company's turnover (sometimes even more)
for many years. This did not go unnoticed to the rest of the personnel of
NRP and CHL, 3 who believed that the NRP just made
test equipment for the US Military [9].
According to some people, 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 unaware.
Besides, the NRP had an armed guard on site and were under surveillance
of the Dutch Army during the night.
➤ More about the NRP
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During his wartime resistance work, Louis Einthoven was known as
The Colonel.
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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.
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At the time, the Christiaan Huygens Laboratory (CHL) was a subsidary of
the NRP, located in an adjacent building. Today, CHL is an independant
company.
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CIA research on EASYCHAIR
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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 at the request of the CIA.
Once approved, the work could commence.
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Shortly after The Thing
had been discovered in Moscow, the CIA was
briefed on the matter by the
Federal Bureau of Investigation (FBI).
During the investigation, the CIA was kept up to speed
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 EASYCHAIR [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].
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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 provided to the NRP
in July 1955, along with the report
[8].
➤ Read the complete uncensored CIA report
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Mylar, or BoPET, is a very strong and stable thin polyester film.
➤ Wikipedia
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NRP research on EASYCHAIR
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Based on the information provided by the CIA [8], the NRP was unable
to create a reliable replica of the Thing in 1955. Instead
they investigated other possibilities.
After initial experiments with 10 GHz (3 cm) signals had failed due to
the high damping of the walls of a building, an operating 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.
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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 late 1955. 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 3-stage
microphone amplifier, the load of which caused the reflected signal
to be Amplitude Modulated (AM).
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 three decades.
➤ More about Easy Chair Mark I
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Stricktly speaking, the device no longer was a Passive Element
in the sense of the Thing, as active components
(transistors) were involved. However, as it didn't need its
own local power source, they kept referring to it as a Passive
Element, or PE.
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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 finally EC Mk V.
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Easy Chair Mark V modulated the sound from the
microphone onto a frequency-modulated (FM) subcarrier, allowing
multiple bugs in the same target area
to be received simultaneously at the listening post. They were
activated by a 500W transmitter in combination with a 14dB corner reflector
antenna, resulting in an ERP of 10kW.
In 1965, about ten years after starting to work for the CIA,
the NRP had managed construct a reliably
working replica of The Thing,
and presented their Pulsed Cavity Microphone.
One model for 360 MHz and one for 1100 MHz.
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Unfortunately, their efforts never got beyond the prototype stage.
In the preceeding years, both the Americans and the Russians had accused each
other of 'bombarding' the other party with excessively strong radio signals (RF).
In some cases this had reportedly led to health issues among embassy
personnel. As a result, the CIA was no longer interested in this type of
device.
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Although the early (passive) EASYCHAIR 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 beam that sooner or later would be noticed by the target.
The NRP therefore started its own
research in the field 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, and have the ability
to turn the device ON and OFF remotely.
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Furthermore, it was thought that any new devices should have the ability
to mask the audio modulation,
so that they could not be picked up with
a standard surveillance receiver
[7]. The research resulted in a range of
useful and innovative new techniques that were interesting enough for the
CIA to keep doing business with the NRP for several decades.
Due to the secret nature of the work,
it was not possible for the NRP engineers to apply for patents 2 at the time.
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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.
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During our research into the history of the NRP, we have found many
creative and innovative designs, that have only recently been patented
by other parties. The actual inventions however, were done at the NRP
several decades earlier, but could not be published and/or patented at the time.
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Russian Embassy in The Hague
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In 1958, in a joint operation of the CIA, the BVD and the NRP,
the Russian Embassy in The Hague (Netherlands) was successfully
bugged for more than 6 months with an Easy Chair III device.
The ambassador had just ordered new furniture for his office and the BVD
succeeded in hiding a Easy Chair III in one of the legs of
a desk. It was activated by means of a powerful transmitter located at an
attic some 100+ metres away [7].
➤ Read the full story
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Russian Embassy in Washington
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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, and that
instead they (the Russians) were bugged by the Americans.
At the press conference they showed a variety of captured bugs,
one of which can be identified as a
Easy Chair SRT-56 device of 1971/1972.
➤ Read the full analysis
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Known Easy Chair products
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Early Easy Chair products
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Complete surveillance systems
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EC
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Easy Chair
Codename for the CIA's early research into resonant cavity microphones,
between 1952 and 1955. Also the global name for the long-term research
contract between the CIA and the NRP. In addition, some products made by
the NRP carried the name Easy Chair or EC.
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CP
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Carrier Pigeon
Method of carrying speech modulation in the activation beam of an Easy
Chair installation, effectively creating a two-way system.
Carrier Pigeon, or CP, was used in the EC II system.
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DP
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Dirty Pulse
Audio masking scheme,
based on Pulse Position Modulation, in which random
noise is added to the rising edge of each pulse.
➤ More
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JJ
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?
Details currently unknown.
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MB
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Music Box
Slot antenna for Easy Chair, developed by CIA (November 1956).
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O
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Omelette
Development of an alternative voice scrambler system, that defeats
existing classical decrambling methods. September 1956.
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PP
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Pied Piper
Research project for the development of a remote controlled radio bug
that used the TP audio masking scheme.
The project eventually led to the development of the SRT-40.
➤ More
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RC
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Rocking Chair
System for bugging a room by connecting a Passive Element(PE) to an
analogue telephone line and activating it with a
WEC device
connected at a tapping point.
➤ More
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RP
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Rejected Pulse
Audio masking scheme,
based on Pulse Position Modulation, in which noise
is used to randomly reject some of the pulses. This is arguably one of the
most effective analogue audio masking schemes ever developed.
➤ More
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SP
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Super Pulse
Research project for an alternative
audio masking scheme based on Pulse
Position Modulation — later merged with Dirty Pulse (DP) —
and miniature transmitter.
➤ More
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TP
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Triple Pulse
Audio masking scheme,
based on Pulse Position Modulation, involving
the use of three consecutive pulses. This masking scheme was also used
by Pied Piper (SRT-40).
➤ More
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AM
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Amplitude Modulation
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ATE
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Active Target Element
Active bugging device that has its own power source, can be controlled
remotely and has full masking of its audio signal. Also known as
TE.
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BVD
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Binnenlandse Veiligheidsdienst
Dutch internal security service, later renamed to AIVD.
➤ More
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CIA
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Central Intelligence Agency
United Status foreign intelligence agency.
➤ More
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EC
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EASY CHAIR
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.
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ERP
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Effectively Radiated Power
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FBI
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Federal Bureau of Investigation
United States federal law enforcement agency, tasked with the investigation
of federal (cyber) crime, corruption, terrorism and counterintelligence.
➤ More
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FM
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Frequency Modulation
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NRL
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Naval Research Laboratory
Technical research laboratory of the US Navy.
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NRP
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Nederlands Radar Proefstation
Dutch Radar Laboratory, at the time located in Noordwijk (Netherlands).
➤ More
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MI5
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Military Intelligence 5
British internal intelligence agency.
➤ More
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PE
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Passive Element
Covert listening device (bug), that does not require a local
power source. Instead it is powered by the energy from a strong RF signal
beamed at it from a nearby location. Examples are the
russian resonant cavity microphone
and the CIA's Easy Chair devices.
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Potus
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President of The United States
Generic name for the (current) president of the United Status. When male,
his female partner is usually known as First Lady of the United States
(FLOTUS).
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SC
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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).
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SCEL
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Signal Corps Engineering Laboratories
Technical engineering laboratory of the US Army Signal Corps,
based at Fort Monmouth (New Jersey, USA).
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SHF
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Super High Frequency
Common expression for frequencies of 3000 MHz and higher.
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TE
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Target Element
Bugging device that is powered by a local battery or another local
power source. Also known as Active Target Element (ATE).
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UHF
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Ultra High Frequency
Common expression for frequencies in the range 300 - 3000 MHz.
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WWII
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World War II
Also known as World War 2, or the Second World War.
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- I.W. Conrad to Mr. Harbo, Results of laboratory examination
Internal FBI memorandum. 23 September 1952. 1
- Director FBI to POTUS, Release of FBI report on Russian microphone
Official letter, via Matt Connelly, to the US President. 4 December 1952. 1
- Peter Wright, Spycatcher
ISBN 0-440-29504-1. 1987-1988.
- David Wise, Molehunt
ISBN 978-0394585147. 10 March 1992.
- Maurits Martijn & Cees Wiebes, Operation Easy Chair
De Correspondent. 24 September 2015.
- Wikipedia, Louis Einthoven
Dutch. Retrieved October 2015.
- Gerhard Prins, Letter to his heirs
Date unknown, but probably written shortly before his death in April 1993.
Vertrouwelijk (confidential). Published by [5].
- CIA Contracting Group, Report on Research on EASYCHAIR
14 July 1955. Classification status unknown. Not marked as secret.
- Nederlands Radar Proefstation 40 Jaar / 1947-1987
July 1987. Chapter 'Amerikaanse zaken' (American affairs).
- Wikipedia, Theo Tromp
Visited 21 May 2023.
➤ Wikipedia (Netherlands)
- Philip van de Poel, Succes en falen van de Nederlandse inlichtingendiensten
Historisch Nieuwblad, 10 October 2012.
- Cees
, personal letter to Ir. Theo P. Tromp (Philips)
The Hague (Netherlands), 28 October 1952. In Dutch language. 2
- Theo Tromp (Philips), letter to Cees
(in Dutch language)
Eindhoven (Netherlands), 29 October 1952. GEHEIM (secret). 2
- Wikipedia, Robert Watson-Watt
Visited 21 May 2023.
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Released by the FBI under the Freedom of Information Act (FIOA)
on 11 May 2014 (FOI/PA# 1173422-1).
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Obtained from the Dutch National Archives (NA) by
Maarten Oberman in April 2023.
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© Crypto Museum. Created: Tuesday 12 January 2016. Last changed: Sunday, 21 May 2023 - 15:58 CET.
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