Resonant cavity microphone
- wanted item
The Thing, also known as The Great Seal Bug, was a passive
covert listening device,
developed in the Soviet Union
and planted in the study of the
US Ambassador in Moscow, hidden inside a wooden carving of the Great Seal
of the United States. It is called a passive device as it does not have
its own power source. Instead it is acivated by a strong electromagnetic
signal from outside.
The device was codenamed LOSS by the US and
RAINDEER (Северный олень)
by the Soviets .
On 4 August 1945, the
Vladimir Lenin All-Union Pioneer organization 1
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 ally.
It hung in the library at the Residency Spaso House .
Unknown to the Americans however, the carving contained an
HF radio bug of
a novel design, in that it didn't have its own power source and was not
connected via wires. Instead, the device was illuminated by a strong
radio signal from the outside, which powered and activated it. It gave the
bug a virtually unlimited life and provided the Soviets with the best
The bug was finally discovered
by the US State Department in 1952,
three ambassadors later, during the tenure of Amb. George F. Kennan .
In 1951, a British radio operator was monitoring Russian air force radio
traffic, when he suddenly picked up the voice of the British Air Attaché
loud and clear, but a survey of the embassy did not reveal any hidden
A similar thing happened to an American interceptor in 1952,
when he overheared a conversation that appeared
to come from the ambassador's residency at Spaso House.
After a search by the Department of State, the bug
was finally discovered by means of a so-called
crystal-video receiver 2 ,
whilst the Russians were actively illuminating the bug .
The device appeared to be hidden inside the wooden carving behind the
ambassador's desk, and resembled a cylindrical microphone with an antenne
rod connected to it. Tiny holes in the wood under the eagle's beak,
guided the sound to the membrane of the bug that was mounted just behind it.
When the Russians knew that an important meeting would take place,
they parked an unmarked van in the vicinity of the residency 3 and
illuminated the bug. A receiver, tuned to the bug's resonant
frequency, was then used to pick up the conversation
in the ambassador's office.
The discovery of the bug was kept secret for many years, until the
1960 U-2 incident
On 1 may 1960, the Soviets had shot down an American U-2 spy plane over
Soviet airspace, as a result of which the Soviet Union convened a meeting
of the United Nations Security Council, accusing the Americans of spying.
On the 4th day of the meeting (26 May 1960), in an attempt to illustrate
to the council that spying between the two nations was mutual,
American Ambassador to the UN, Henry Cabot Lodge,
revealed the Russian bugging device,
as shown in the photograph above.
The Vladimir Lenin All-Union Pioneer Organisation, also known as the
Young Pioneer organization, was a mass youth organization of the Soviet
Union for children between 10 and 15, similar to the Scouting
organizations of the Western world .
A crystal-video receiver
is a non-selective or aperiodic receiver .
In some literature it is suggested that the device was 'illuminated'
from a building across the street, rather than from a nearby parked van.
The Thing is a so-called resonant cavity microphone, consisting of a
resonant cavity, combined with a condenser microphone.
The diagram below shows an 'educated guess' of the construction of The
Thing, based on various reports and publications. The device consists
of a copper cylinder with a highly polished silver-plated interior, that
acts as a high-Q resonant cavity of the reentrant type.
At the center is an adjustable mushroom-shaped
disc with a flat surface, acting as a capacitor in combination
with a very thin 75µm membrane that closes the open end. An antenna enters the
cavity through an insulated hole in the side of the cylinder and is
The cavity has a diameter of 19.7 mm and is 17.5 mm long. The antenna
is ~22.8 cm long (9").
The membrane, or diafragm, at the front of the
cylinder is just 75 micrometers thick (3 mil). The tuning post can be
adjusted to increase or decrease the capacity of the mushroom. The flat
face of the mushroom has machined grooves to reduce the pneumatic
damping 1 of the diafragm.
According to one report , the distance between the mushroom and the
diafragm was 230µm.
The dimensions of the cavity are carefully chosen so that it is resonant
at a very high frequency (e.g. 1320 MHz).
It is then illuminated, or exited, by a strong signal
from the outside, as shown in the illustration below.
Any sound in the room (speech) causes the membrane to vibrate,
which decreases and increases the space inside the cavity and also
the capacity between the membrane and the mushroom. As a result, the bug
produces a combination of Amplitude Modulation (AM)
and Frequency Modulation (FM). In practice, only the AM component
was used by the Russians.
It is currently unclear what the illumination frequency was.
In the original investigation reports, it is suggested that the
illumination frequency was the same as the resonance frequency (i.e. the
output). Although this poses technical restrictions, such as
overloading of the receiver, it is the most likely scenario.
Receiver overloading can be solved by using directional antennas
(e.g. helical antennas)
and by mixing part of the transmitted signal with the input
of the receiver, in order to cancel-out the excess signal.
The block diagrams below give some useful suggestions.
The antenna problem can be solved effectively, by adding a 3-pole
circulator between the transmitter and the receiver, as illustrated
in the diagram below. The circulator ensures that all transmission
power is passed to the antenna and that returned energy is passed to
In practice, it would also be possible to use a sub-harmonic of the
resonance frequency as the illumination signal. Such sub-harmonics are
often easier to generate at high power, and cause far less interference
between transmitter and receiver. Take for example
440 MHz, which is 1/3 of the resonance frequency of our example above. 2
In that case, the cavity is used as a tripler.
In order for the cavity to generate the 3rd harmonic of the exitation
frequency, it must have nonlinear properties, such as loose contacts
or thin oxidized layers between contacts, similar to a semiconductor
(diode). In that case the cavity would act as a
so-called contact generator. In the given situation, this effect
is arbitrary however, and its behaviour would be difficult to predict and
reproduce. It is therefore unlikely that the cavity was used as a multiplier.
Pneumatic damping is also known as the cushion effect.
Although it is possible to use other sub-harmonics,
the 2nd and 3rd sub-harmonic are the most likely candidates
as oxidised metals can easily generate the 2nd and 3rd
harmonics of the input signal.
The resonant cavity microphone was
Winfield Koch at RCA in 1941 1 .
The actual Russian bug was developed by Léon Theremin
(27 August 1896 - 3 November 1993),
born in Saint Petersburg (Russia) as Lev Sergeyevich Termen
(Лев Сергеевич Термен) and inventor of the Theremin,
a musical instrument with a proximity sensor, which is shown in the image below .
Theremin lived in the
United States from 1927 onwards, where the theremin was produced by
RCA. He returned to the USSR unexpectedly in 1938, shortly before the outbreak of WWII,
after running into financial and tax problems.
In the USSR, Theremin was first imprisoned, but was later put to work at
a sharashka, a secret laboratory in the Gulag camp system, along with
other detained scientists and engineers, such as
Andrei Tupolev and Sergei Korolev.
There he developed Buran (an infrared microphone),
The Thing and several other devices
for the NKVD.
In 1947 he was released, and in 1956 he was fully rehabilitated by the Soviets.
He kept working for the NKVD (by then renamed to:
KGB) until 1966.
He was a teacher at the Moscow Conservatory of Music and later became Professor of
Physics at Moscow State University. After 51 years in the Soviet Union, he first
visited Europe in 1989 and then the United States in 1991. Early in 1993 he made
his last performance in the Netherlands. He died later that year in Moscow
at the age of 97.
➤ Read the CIA file on Leon Theremin
US Patent 223811
was filed on 14 April 1941, with a priority date of
30 September 1938. As Theremin had also been working with RCA and had
left the US in late-1938, it is possible that he had knowledge of
the patent when he returned to the Soviet Union (USSR).
was the predecessor of the KGB.
The diagram below shows the theoretical equivalent of the resonant
cavity microphone, which is basically a tuned circuit, consisting
of a inductance and a capacitance. Part of the capacitance is variable
as it is effectively a microphone. The antenna is capacitively coupled to
the tuned circuit.
A lot has been said about the length of the antenna of The Thing.
In the initial FBI investigation it is claimed that the antenna length
is 1½λ ,
whilst a later CIA report specifies it as ½λ .
Some have claimed it should be ¼λ for the exitation frequency
and ¾λ for the output frequency. It has also been suggested
that it is a full wave-length (1λ).
As the final technical report by the FBI and the NRL has not yet been
declassified, the information below is purely speculative.
The table above gives the resonance frequencies of the antenna, if we
assume the antenna to be ideal and 9" long (22.8 cm). In practice, a
correction has to be applied to compensate for the so-called end effect.
If we assume this scale factor to be 0.9, this gives us a
frequency between 1700 and 1800 MHz at 1½λ antenna length,
which is in line with the findings of the FBI Laboratory
Discovery of the Thing
Ever since the Amerasia affair in 1945 , the US was suspicious of
bugs being planted in US embassies abroad, especially in Moscow. Although
quite a few bugs were discovered in US Embassies in Eastern Europe during
the late 1940s, none had been found in Moscow since WWII.
Nevertheless, it was assumed by diplomats that the walls in Moscow had
ears. The suspicions increased in the fall of 1951, when a British
military officer who was monitoring Russian military aircraft traffic,
suddenly heard the voice of the British Air Attaché loud and clear
on his radio.
Engineer Don Bailey of the Diplomatic
Wireless Service (DWS) was sent to Moscow to investigate the
matter, but no bugs were found. The Russians clearly had been warned
and had turned the device off.
Nevertheless, Bailey reported the presence of strong RF radio signals
when the device was in operation, which led the British to believe that
the Russians (like they themselves) were experimenting with some kind of
resonance device instead of a regular transmitter [8 pp. 24-25].
Shortly afterwards, a US military officer had a similar experience
when he suddenly overheard a conversation that appeared to originate from the
ambassador's study at Spaso House, the residency of the US Ambassador
in Moscow. The matter was investigated by John Ford and Joseph Bezjian
of the Department of State's security team, but they didn't find
anything [20 p. 136].
Early in 1952, after George Kennan had been appointed the new US Ambassador
in Moscow, Spaso House was being refurbished for him,
and Soviet workers were hired to carry out the work.
Kennan believed this provided the Soviets an opportunity to plant
listening devices (bugs), and ordered regular sweeps.
Nevertheless, repeated technical security inspections found nothing.
In September 1952, Joseph Bezjian returned to Spaso House for a more
extensive search. As he believed that the Russians had removed the bugs
prior to the arrival of the previous search team, he posed as a
'house guest' for three days and had his equipment sent in
ahead of his arrival.
In a pre-arranged plan, the ambassador dictated an unclassified
piece of text, whilst Bezjian searched the premises with his
crystal video receiver. 1 Using this receiver he was finally able
to locate the bug in the Ambassador's study.
The study was sometimes used as a sitting room and,
in 1947, as a temporary office by Secretary
of State Marshall, during the Council of Foreign Ministers in
Moscow. Marshall preferred to work undisturbed and liked the casual
arrangement of the furniture. It is quite possible that the Soviets
gained valuable intelligence from his presence.
When Bezjian inspected the room on 10 September 1952, 2
the signal appeared to come from the wall behind a wooden
carving of the Great Seal of the United States in a corner of
the room. After taking the seal from the wall,
the signal disappeared and Bezjian finally realised that
the bug was hidden inside the seal itself and that it was
remotely (de)activated from outside the building.
After a close inspection of the wooden carving, Bezjian discovered
that it could be opened and that the bug was mounted in a cut-out
space inside it. At first inspection, the bug resembled a microphone
with an antenna attached to it. It did not have any wires or an
external power source connected to it.
To avoid it being stolen, Bezjian slept with the device under his pillow
The next day, the mysterious bug was sent to Washington (US),
where it was handed over to the FBI for further investigation.
As it was intially unclear
how the device worked - it didn't have any active components - it was
nicknamed The Thing. The FBI sent the device to their
Technical Laboratory where it was inspected by personnel of
the Radio and Electric Section. The preliminary
conclusions were that it was a resonant cavity microphone,
operating between 1650 and 1800 MHz
and that the antenna had a length of 1½λ.
Together with the Naval Research Lab (NRL),
the FBI would later submit a detailed report about the thing,
which was shared with other agencies.
President Truman ordered the NRL to develop
that would be able to detect and locate passive cavity resonators.
Although the Division of Technical Services of the Department of
State's Office of Security (O:SY/T) was heavily understaffed in
1947, by 1961 the division had 15 SY-engineers. Between 1948 and
1961, these SY engineers were responsible for more than 95% of all
listening devices found by all US Government agencies together [20 p. 163].
A crystal-video receiver
is a non-selective or aperiodic receiver .
In the official History of the Bureau of Diplomatic Security
of the Department of State it is claimed that the bug was found
on 12 September. However, we believe this to be incorrect, as the
discovery was already mentioned in an internal FBI memo of
11 September. It is more likely that the device was
discovered on the day before the memo, on 10 September 1952.
After the Russians had shot down an American U-2 spy plane over Soviet
airspace on 1 May 1960, an incident that became known as the
1960 U-2 incident , they convened a meeting of the
Security Council at the United Nations,
claiming that the US had been spying on them.
In order to demonstrate that spying was mutual, the American's decided
to disclose the Soviet bug, known as The Thing, that was found
at the ambassador's residency in Moscow 8 years earlier.
The revelation of the high-tech Russian device attracted the attention of
the international press and made the headlines during the next days and weeks.
The short film above is a clip from a Universal-International News reel
found on YouTube in September 2015 .
It has often been suggested that US officials had no idea how the device
worked and that they turned to the UK for help .
There is sufficient evidence from official reports however,
to assume that the various US agencies had thouroughly investigated the
device and had a good understanding of its operation.
The following agencies each performed their own investigations:
- Department of State
The device was first discovered at Spaso House by technician
Joseph J. Bezjian
of the Division of Technical Services of the Office of Security of the Department
of State, commonly identified as O:SY/T, when conducting a sweep
in Moscow, under supervision of his chief John W. Ford.
The discovery was immediately reported to the FBI.
The day after the discovery, the device was flown to Washington (USA),
where it was handed over to the FBI.
Personnel of the Radio and Electrical Section
of the FBI's Technical Laboratory then investigated the device on 16 and 17
September 1952. Their preliminary findings are presented in an internal
FBI memo of 23 September and in the final technical report on 1 December 1952.
By that time, the FBI had two working replicas of The Thing.
After the initial investigation by the FBI, a more comprehensive one
was conducted jointly by the FBI Technical Laboratory and the Naval
Research Laboratories (NRL). This resulted in a detailed technical report
that was released on 1 December 1952. Furthermore, the NRL was asked to
develop suitable countermeasures equipment.
Based on FBI drawings supplied to them at an early stage of the investigation,
the Signal Corps Engineering Laboratories (SCEL) successfully built a working
cavity microphone with excellent audio performance, working on 1100 MHz.
The FBI was informed of this.
The CIA was briefed by the Department of State (DoS) shortly after the
device had been discovered. They were also part of a Special IIC-ICIS-CIA
Committee (SC) that had to investigate the security problems posed by The Thing.
The CIA later started its own investigation and initiated a research project
under the name EASY CHAIR,
with the aim to produce devices similar to The Thing,
that could be used to the advantage of the CIA.
The British Intelligence Service MI5 was contacted by the Americans
soon after the discovery of the device, but it is unclear which US agency
was responsible for the contact. It is likely however,
that they were briefed by the FBI.
It allowed Marconi Engineer
to develop a British equivalent of the device under the codename
At the time The Thing was discovered, the
had just been established as
the successor to the AFSA. Although it is certain that NSA officials were
aware of the discovery, it is currently unknown whether they conducted their
- Bell Labs
During a meeting at SCEL
on 15 December 1952, it was mentioned that
Bell Telephone Laboratories (Bell Labs)
had developed a device for modulation
of a microwave carrier by changing the physical size of a wave guide section.
No capacity was used and it did not appear to be of much use to the FBI
at the time.
Although many agencies are claiming their involvement in the discovery
of The Thing, the device was actually found by the Department of State
(DoS), during a staged undercover security sweep in September 1952.
Although resonant cavities were known in the field of radar,
their use as bugging devices was completely new. DoS security technician
immediately realised this, and secured the device so that
it could not be stolen by the Russian staff at Spaso House.
The day after the discovery, the device was sent to Washington (USA),
where it was handed over to the FBI for further investigation.
The information gained from this investigation was later used to educate
the various agencies in the detection and discovery of similar devices.
On 5 December 1952, after the investigation was completed, the device
was returned to the DoS .
A former Foreign Service officer recalls it was
on display in the SY's conference room in the 1960s .
The first agency to investigate the device after its discovery by the
Department of State, was the
Federal Bureau of Investigation (FBI).
The day after the device was
discovered by the Department of State's Joseph Bezjian, it was flown to
Washington, where it was handed over to the FBI.
It was subsequently examined on 16 and 17 September 1952 by personnel
of the Radio and Electrical Section of the FBI's Technical Laboratory,
who reported the following on 23 September :
It was found that the 'ultramodern radio transmitter' consisted
of a cavity resonator with a condenser microphone built into the high
impedance end of the cavity and with a 1½ wave length antenna extending
out the side of the cavity. It was immediately apparent that the
device was designed for use as a microphone unit without any external
wire connections by beaming a UHF radio signal of suitable strength and
frequency toward the antenna of the unit and by using suitable UHF
radio receiving equipment which would pick up and demodulate the re-
radiated and modulated signal emitted by the antenna of the device.
Determining the operating frequency of the device had not been easy
as the Bureau's equipment was not suitable for frequencies above
400 MHz. Luckily, they were able to borrow the following test equipment
from the National Bureau of Standards (now: NIST) for the period
of one day:
- Power oscillator, Airborne Instruments Laboratory type 124, 300-2500 MHz
- UHF Signal Generator, Hewlett-Packard model 610A, 400-1200 MHz
- Tuning unit, TN-19/APR-4, 975-2200 MHz
- Tuning unit, TN-54/APR-4, 2150-4000 MHz
The most important conclusions of this preliminary investigation were:
- Cavity resonator with built-in condenser microphone
- 1½λ antenna length
- Frequency between 1650 and 1800 MHz
- Good quality of speech
- Very sensitive, good pickup range
A day earlier, on 22 September, by special orders from the President,
a Special Committee (SC) had been formed to investigate the security
problems posed by the device. The SC consisted of the IIC,
the ICIS and
and was chaired by Special Agent Edward S. Sanders of the FBI.
At the first meeting, on 1 October 1952, all parties were
briefed on the FBI's preliminary findings.
On 3 November 1952, the FBI conducted a 45 minute briefing for technical
personnel of the Office of Special Investigations (OSI) 1 in which the
characteristics of The Thing were explained, in the hope that they
might be able to recognise the devices in the field. This is what we learn:
- Operating frequency: 1700 MHz
- The device has serial number 11
- Device has been tested over a distance of 75 feet (23 metres)
- Only one device has been found so far
- It is unknown whether copies have been made
- Countermeasures are being developed
By the time the final technical report is ready on 1 December 1952
(see below), the FBI has two working copies of the Russian cavity
microphone. These copies may have been used by the FBI for the development
of devices for their own use, but may also have been passed to other
agencies. It is assumed that the CIA produced its own
prototypes based on drawings supplied by the FBI.
The name OSI (Office of Special Investigations) is shared by several
government agencies, such as the Air Force and the Department of
and final FBI technical report
One of the first organisations to be involved in the investigation
besides the DoD and the FBI is the Naval Research Laboratory (NRL),
which works in close cooperation with the FBI during the technical
investigation. A number of FBI Special Agents are actually at work at
the NRL facilities.
In order to avoid duplication of efforts, the NRL is instructed to develop
a countermeasures receiver
that will be able to detect resonant cavity
microphones. Although the NRL will not take these receivers into
production, they will present a working prototype.
On 1 December 1952, the final top secret FBI/NRL technical report 1
is ready . It contains the following information:
- Report of the FBI Laboratory's analysis and experiments
- Detailed scale drawings and photographs
- NRL report with design of countermeasures equipment
Numbered copies are distributed to the following people:
- President of the United States (via Matt Connelly)
- John W. Ford, Department of State
- John W. Ford, Department of State
- Rear Admiral Carl F. Espe, Director of Naval Intelligence (ONI)
- Major General Richard C. Partridge, Assistent Chief of Staff (Army)
- Major General Joseph F. Carroll, Director Special Investigations (ASAF)
- General Walter Bodell Smith, Director, Central Intelligence Agency (CIA)
- Interdepartmental Committee on Internal Security (ICIS)
- Gordon E. Dean, Chairman, Atomic Energy Commission (AEC)
- John W. ??? 2
Unfortunately, the actual report has not yet been released (2016).
The Signal Corps Engineering Laboratories (SCEL) have been informed by
the FBI at a very early stage. They were briefed on the current status
of the investigation during a meeting of the IIC-ICIS-CIA Special Committee (SC)
on 1 October 1952. As the FBI is urgently looking for a microwave transmitter,
they are allowed to borrow one from the SCEL at Fort Monmouth (NJ).
After the final technical report of the FBI has been completed on 1 December 1952,
the borrowed equipment is returned to the SCEL on 15 December 1952 by
of the FBI. On this occasion the FBI report was discussed along with the
possibility for future work in this area.
Based on the drawings of the Russian cavity microphone that were supplied
by the FBI, the SCEL had been able to built a working replica of it. The
unit worked at 1100 MHz and had an excellent audio sensitivity, not least
because the membrane was placed just 25 µm (1 mil) 1 from the disc.
The device had been tested through a plywood wall with a low power transmitter,
and produced an AM signal with approx. 50% modulation depth.
No Frequency Modulation (FM) was noticed.
In the original Russian design, the distance between the membrane and
the mushroom shaped disc was approx. 250 µm (9 mil).
During the FBI investigation, the CIA is kept informed
of the latest FBI progress, via the SC meetings.
This means that they had
access to the results of the preliminary FBI investigation, as well as
to the final report of 1 Dec 1952.
Based on this information, the CIA started its own research project
with the aim to develop listening devices based on the principle of
the resonant cavity microphone.
The project was codenamed EASY CHAIR and was partly
carried out by a laboratory in The Netherlands, as David Wise mentiones
in his book Molehunt .
In September 2015, the Dutch online magazine De
Correspondent revealed that EASYCHAIR
was carried out at the
Dutch Radar Laboratory (NRP)
in Noordwijk .
Between 1955 and 1992, the NRP produced a wide range of innovative
covert listening devices (bugs)
for the CIA, starting with the
Easy Chair Mark 1, or EC Mk 1, in late 1955.
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 detailed discription of their operation.
The image on the right was extracted from that report .
Interestingly, the antenna length is specified by the CIA as λ/2
whereas, according to the preliminary FBI report, it had a length
➤ More about EASYCHAIR
In his book Spy Catcher , former MI5 scientific officer
gives an account of how he was approached by
in 1952 1
to find out how The Thing worked. Apparently the CIA and FBI
had no idea of the operating principle behind it and had
presented the device, or a replica of it, to MI5.
Wright, who was still employed at the Marconi Company in Great Baddow
(Essex, UK) at the time, reverse engineered the device after work hours
and it took him ten weeks to solve it.
Once Wright had figured out the principle, he was able to
demonstrate it to his contact at MI5.
In the next 18 months he developed a British equivalent that
would become known as SATYR.
Using two British umbrellas as
transmit and receive antennas, Wright called it Black Magic.
Several complete SATYR sets, with matching transmitters and receivers,
were ordered by MI5 and were subsequently used by the British, Australian
and Canadian intelligence services throughout the 1950s and probably the
According to Wright's own account, the CIA ordered twelve complete sets
and rather cheekily copied the drawings to make twenty more themselves.
According to Wright, the American variant was called EASY CHAIR
(also Mark 2 and Mark 3).
This is contradicted by former CIA technical officer Peter Karlow however,
who states that MI5 never shared its discovery with the CIA .
It is currently unclear which American agency was responsible
for the contact with MI5 and/or
Although it is often assumed that
it was the CIA who put the matter before him, it might also have been
the FBI or the State Department. If Wright had been given the original
device during the 2nd half of 1952, his contact was most likely the FBI as
it was in their possession from 12 September to 5 December 1952.
But they could also have given him a replica, as it is certain that the
FBI had several of them by 1 December 1952.
In any case, this would explain why, according to Karlow,
the CIA was not aware of any work carried out in the UK .
As the CIA was frequently updated
by the FBI during the investigation,
via the IIC-ICIS-CIA Special Committee (SC),
it is also possible that the CIA's Technical Services Division (TSD)
was able to build a functional replica at an early stage,
and that this replica was supplied to MI5 and Wright.
However, in that case the CIA must have been aware of
the British research and its outcome.
There are indications that the British were indeed briefed on the subject,
as confirmed in (partially declassified) letters from the FBI office in
London (UK) of 6 October,
and finally of 8 December 1952
. The latter also suggests that the British had their own
research, as they promise the FBI to keep them informed of any local
developments as part of their cooperation. If this is the case, it is likely
that Wright was contacted (via MI5) by the FBI rather than by the CIA.
It is possible, if not likely, that Wright was not presented the full
picture by the Americans and/or British intelligence,
and that similar research projects, carried out by other parties,
were kept from him, leading him to believe that he solved the case
for the Americans entirely by himself.
It is also possible that Wright did solve the mystery for the FBI
and that the US kept it secret.
➤ More about SATYR
In 1952, Peter Wright was officially employed as a Navy scientist,
attached to the Marconi Company at Great Baddow (Essex, UK)
working under government contract on naval radar
systems. He was frequently consulted in secrecy by MI5. In 1954 he became
the first principal scientific officer of MI5 .
Immediately after the discovery of the Russian resonant cavity microphone,
the FBI started an all-out investigation; one of the most difficult projects
in their history .
At the same time, the Naval Research Laboratories (NRL),
who were helping the FBI with their research, were ordered to develop a
countermeasures receiver that could be used to find resonant cavity microphones.
Details of a suitable countermeasures receiver are included in the final
FBI/NRL Technical report on the Russian resonant cavity microphone.
Unfortunately, this part of the report still has not been released (2016),
so we are unable to provide any technical details about it at present.
During the course of the development, part of the technical staff of the
FBI Laboratory worked at the NRL facilities in Washington. In particular
Ivan Conrad and Special Agents Sutton, Swartz and Bradley, are commended
for their excellent technical contributions, as well as the NRL team
supervised by Captain Beltz. They have completed their work in a very
short time frame.
Although the NRL has developed a suitable countermeasures receiver,
and may have delivered one or two prototypes, they are not equipped for
series production of such a device.
It is therefore decided that the Atomic Energy Commission (AEC)
will build the actual receivers, but getting a price quotation from them,
and determining how many receivers should be ordered, appears to be
difficult . Apart from the receivers, special microwave
generators, manufactured by the General Radio Company,
were required in order to activate any cavity microphones .
In any case, the FBI does not posess a complete countermeasures set
by January 1953, as they are not able to allocate the necessary funds
for purchasing the required generators in December 1952 .
When the White House asks the FBI to perform
a security survey of the White House in January 1953, they have
to reconsider their decision for not buying the generators .
Being the first users of resonant cavity microphones, the Russians realised
that, once the devices were discovered, they would be copied by Western
agencies, and that sooner or later they would be used against themselves.
The Soviets therefore developed their own countermeasures.
An example of a Russian countermeasures receiver that was developed especially
for the detection of resonant cavity microphones, is the
OSOBNJAK 8 shown in the image on the right.
The device is housed in an unobtrusive briefcase and can detect strong nearby
RF signals between 100 MHz and 12 GHz; the signals that are typically used to
activate such microphones.
➤ More about Osobnjak 8
In most cases, it will be sufficient to know that a strong microwave signal
is present, so that the meeting can be moved to a different location, or
can be cancelled altogether. In some cases however, the bugged party might
want to know who is eavesdropping on them, and from which location the
activation beam is sent. The suitcase is not suitable for
direction finding however.
In order to find the location of the illumination signal (i.e. the
activation beam), one would need an aperiodic receiver 1 for the suspected
band, plus an antenna with a narrow viewing angle.
A suitable solution was the
MRP-4 radar locator,
developed by Tesla in
in 1972. This device can be worn on the chest,
with the antennas facing forward.
Although originally developed for finding radar stations, it can be
used for locating any nearby strong transmitter.
➤ More about the MRP-4
The antennas of the MRP-4 have a very narrow viewing angle, typically
between 1 and 2 degrees, making it very easy to determine the direction
to the transmitter. The device is suitable for the 1 - 10 GHz frequency
range, divided over four bands. Similar devices were developed in the USSR.
Also known as a crystal video receiver.
The following abbreviations and expressions are used in connection with this page:
Atomic Energy Commission
Central Intelligence Agency
Director of the FBI
At the time of the event, this was J. Edgar Hoover.
Department of State
Research project, initiated by the CIA in 1954, to develop covert
listening devices based on the experiences with The Thing.
The codename Easy Chair was also written as EASYCHAIR or EC.
The actual research was carried out by the
in The Netherlands.
Federal Bureau of Investigation
Interdepartmental Intelligence Conference
Resides under the NSC.
Interdepartmental Committee on Internal Security.
Resides under the NSC.
The codename JUNE was used by the FBI for information about covert
microphones found in US Embassies abroad, from 1947 onwards. The discovery
of The Thing in 1952 is documented in the FBI archives under the codename
JUNE as well.
US codename for 'The Thing'
According to Keith Melton , the American codename for the Soviet
covert listening device, a.k.a. 'The Thing', was LOSS.
Military Intelligence 5
British internal intelligence agency.
Naval Research Laboratory
Technical research laboratory of the US Navy.
National Security Council
President of United States
Russian codename for The Thing (Северный олень).
Common expression used for Special Agents of the FBI.
Temporary commission, established by the President of the
consisting of the two internal security committees
of the National Security Council, the IIC
and the ICIS, in collaboration
with the CIA,
tasked to examine the security problems posed by The Thing.
Also known as the IIC-ICIS-CIA committee.
Signal Corps Engineering Laboratories
Technical engineering laboratory of the US Army Signal Corps,
based at Fort Monmouth (New Jersey, USA).
The following people are frequently mentioned on this page and/or the
documents that are referred to in the text. This list is by no means
Belmont, Alan H.
Joined the FBI in 1936. At the time of the discovery of The Thing he was
the head of the Domestic Intelligence Division of the FBI in Washington.
Bezjian, Joseph J.
Technical Engineer at the Division of Technical Services (T) of the
Office of Security (O:SY) of the Department of State (O:SY/T)
who actually discovered The Thing in the ambassador's study at
Spaso House in September 1952. Nicknamed: The Rug Merchant.
Ford, John W.
Head of the Division of Technical Services of the Office of Security
of the Department of State (O:SY/T).
Conrad, Ivan W.
Head of Division 7 of the FBI's Technical Laboratory.
Assistent Director of the FBI. Commonly referred to as Mr. Harbo.
Hoover, John Edgar
Director of the FBI. Commonly referred to as DIRFBI or
Ladd, D. Milton
Joined the FBI as an agent on November 1928.
At the time of the discovery of The Thing he was Assistant to the
Director of the FBI (i.e. the number 3 of the FBI).
British Navy scientist, attached to the Marconi Company, who works
part-time for the British intelligence service MI5. He later becomes
MI5's first Principal Scientific Officer.
In order to help putting this complex story together, we have used
the following chronological list of events as a guide:
4 Aug 1945
Great Seal Bug planted at Spaso House
The Vladimir Lenin All-Union Pioneer Organisation presents a hand-carved
replica of the Great Seal of the United States to
US Ambassador Averell Harriman, who hangs it in the study of
his Moscow Residency Spaso House.
8 Sep 1952
Suspected penetration of the US Embassy in Moscow
Letter from John Edgar Hoover to John W. Ford,
about the suspected penetration of the US Embassy in Moscow
10 Sep 1952
Discovery of The Thing 1
An ultra modern listening device is discovered by US Department of
State technician Joseph Bezjian, whilst conducting a pre-arranged
sweep at Spaso House, the residency of the US Ambassador in Moscow.
11 Sep 1952
FBI internal memo about discovery of The Thing
Internal FBI memo from AH Belmont to DM Ladd (not released).
16-17 Sep 1952
Preliminary investigation by the Technical Laboratory of the FBI
The preliminary findings
are reported on 23 September 1952.
22 Sep 1952
Formation of IIC-ICIS-CIA Special Committee
The President orders the creation of a
Special Committee (SC),
consisting of the IIC,
and the CIA.
The SC has the task to examine security problems related to
the discovery of The Thing.
23 Sep 1952
Internal memo with preliminary findings
Internal FBI memo from IW Conrad to Mr. Harbo
1 Oct 1952
First IIC-ICIS-CIA Meeting (SC)
Meeting in which the chiefs of staff are briefed on the topic.
Present are representatives of the Army, the Navy, the Air Force
and the National Security Council. SA Edward S. Sanders is later
appointed chairman of the SC.
6 October 1952
Progress report to POTUS
The Director FBI informs the President of the United States about
the excellent technical progress that has been made by the FBI
and the NRL.
13 Oct 1952
Development of 'resonant cavity'
The FBI wants to advise the Domestic Intelligence Division on
how soon resonant cavities and their activating devices can be made
available for their own purposes.
15 Oct 1952
POTUS asks FBI to inform the SC
In the light of the technical progress that was reported on
6 October, POTUS asks the FBI to keep the IIC-ICIS-CIA committee
informed (partly released).
23 Oct 1952
Request for OSI briefing
The Chiefs of Staff suggest that it might be a good idea to
brief their overseas technical personnel, so that they can recognise
the devices in the field (partly released)
24 Oct 1952
Briefing in the UK
Report from the Legal Attaché in London to the Director of the FBI,
about discussing The Thing with the British Government
28 Oct 1952
Visit of UK representative to FBI
Following the briefing of the UK Government on 24 October,
a representative of the British Government has visited the FBI
in relation to the device.
3 Nov 1952
Briefing of the OSI
Briefing of technical personnel of the Office of Special Investigations
(OSI) of various government agencies, conducted by Special
Agent R.W. Swartz of the FBI. During this 45 minute briefing, the FBI
explained the technical characteristics of The Thing to the OSI
1 Dec 1952
Final technical report ready
Detailed technical report about the investigation of the device,
jointly carried out by the FBI and the NRL (not released).
4 Dec 1952
Distribution of final report to controlled group
The report is made available to the President of the United States,
Mr. John Ford of the Department of State, the various members of the
Interdepartmental Committee on Internal Security, the Director
of the CIA and the Chairman of the Atomic Energy Commission.
5 Dec 1952
Cavity microphone returned to Department of State
After finishing the technical report on the cavity microphone,
the FBI returns the Great Seal of the United States with the
hidden Russian resonant cavity microphone to the Department
of State (released)
8 Dec 1952
Local developments in the UK
Through the US Embassy in London, the FBI is advised of local
British developments in this area
15 Dec 1952
Test equipment returned to SCEL
After finishing the investigation, the equipment that was borrowed
from the Signal Corps Engineering laboratories (SCEL) is returned by
FBI Special Agent Swartz. On his visit, SCEL demonstrates a working
16 Jan 1953
IIC-ICIS-CIA Special Committee meeting
Discussion about the production of countermeasures equipment by
the Atomic Energy Commission (AEC)
12 Feb 1953
White House request for sweep
The White House asks whether the FBI is equipped to make a security
survey of the White House for the detection of cavity microphones
In the official history of the Department of State, it is claimed
that The Thing was found at Spaso House on 12 September 1952.
This is believed to be incorrect however, as its discovery is
discussed in an internal FBI memo as early as 11 September 1952
- Wikipedia, The Thing (listening device)
Retrieved September 2015.
- Wikipedia, Vladimir Lenin All-Union Pioneer Organization
Retrieved September 2015.
- Kevin D. Murray, The Great Seal Bug Story
Retrieved September 2015.
- Anonymous contributor 2, Description of the Great Seal Bug
Former US Army Sergeant and radar repairman.
Retrieved from , September 2015.
- Wikipedia, 1960 U-2 indicent
Retrieved September 2015.
- Wikipedia, Léon Theremin
Retrieved September 2015.
- Winfield R. Koch, US Patent 2238117
Ultra high frequency modulator (resonant cavity microphone).
30 September 1938. RCA Corporation.
- Peter Wright, Spycatcher
1987-1988. ISBN 0-440-29504-1.
- YouTube, UN Spy Debate. Reds 'Bugged' American Embassy Lodge Claims.
1960. Published 14 February 2014. Retrieved September 2015.
- Robert Wallace & H. Keith Melton, Spycraft
ISBN 978-0-55382-007-2. p. 165.
- David Wise, Molehunt
10 March 1992. ISBN 978-0394585147.
- Passive Resonant Cavity & 'Spycatcher' Technical Surveillance Devices
Website: GBPPR Homebrew Military & Espionage Electronics.
Visited October 2015.
- Maurits Martijn & Cees Wiebes, Operatie Leunstoel
De Correspondent. 24 September 2015.
- Anonymous contributor (former US Service Officer), Description of the Great Seal Bug
The Great Seal Bug Story, Part I. Compiled by Kevin D. Murray.
29 April 2012. Retrieved September 2015.
- W.E. Ayer, Characteristics of Crystal-Video Receivers Employing R-F Preamplification.
Stanford University. Technical report No. 150-3. 20 September 1956.
Obtained via 
Declassified uder DoD Directive 5200,20.
- Graham Brooker & Jairo Gomez, Lev Termen's Great Seal Bug Analyzed
November 2013. IEEE A&E Systems Magazine. pp. 4-11.
- John Rooney (AP), Photograph of Henry Cabot Lodge showing 'The Thing'...
...at the United Nations (UN) on 26 May 1960.
26 May 1960. Retrieved February 2014.
- Bettman (CORBIS), idem
26 May 1960. Retrieved September 2015.
- Wikipedia, Amerasia
Retrieved December 2015.
- US Department of State, History of the Bureau of Diplomatic Security
Global Publishing Solutions, October 2011. First Edition. pp. 161-163.
- Federal Bureau of Investigation (FBI), FBI file on Russian Cavity Microphone
Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014.
- Director of the FBI to George C. Marshall, Secretary of State
19 February 1947. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- John Edgar Hoover to John W. Ford, Suspected penetration of US Embassy
8 September 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- IW Conrad to Mr. Harbo, Results of laboratory examination
23 September 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- Matthew Conelly to J Edgar Hoover, Request to inform IIC-ICIS-CIA committee
15 October 1952. Released under the FIOA on 5 August 2015.
- AH Belmont to DM Ladd, Request for OSI briefing
23 October 1952. Released under the FIOA on 5 August 2015.
- DM Ladd to Director FBI, Assignment of SA Sanders as chairman of IIC-ICIS-CIA Special Committee
23 October 1952. Released under the FIOA on 5 August 2015.
- Legal Attaché London to Director FBI
24 October 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- IW Conrad to Mr. Harbo, Briefing of OSI personnel
4 November 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- Director FBI to Legal Attaché London
5 November 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- IW Conrad to RT Harbo, Countermeasures equipment
2 December 1952. Released under the FIOA on 5 August 2015.
- Executives Conference to Director FBI, No funds for building countermeasures equipment
3 December 1952. Released under the FIOA on 5 August 2015.
- FBI receipt, Cavity microphone and Great Seal of the United States handed over
5 December 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- DJ Parsons to Mr. Harbo, Letters of commendation
5 December 1952. Released under the FIOA on 5 August 2015.
- Legal Attaché London to Director FBI
8 December 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- DJ Parsons to Mr. Harbo, Return of equipment to US Army Signal Corps
8 December 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- IW Conrad to RT Harbo, Equipment returned to SCEL
19 December 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- AH Belmont to Mr. DM Ladd, Countermeasures equipment from the AEC
22 january 1953. Released under the FIOA on 5 August 2015.
- WI Conrad to Mr. Harbo, White House security
13 February 1953. Released under the FIOA on 5 August 2015.
- CIA Contracting Group, Report on Research on EASYCHAIR
14 July 1955. Classification status unknown. Not marked as secret.
- Wikipedia, Spaso House
Retrieved january 2016.
- Director FBI to POTUS (via Matt Connelly), Release of FBI report on Russian microphone
4 December 1952. Released under the FIOA (FOI/PA# 1173422-1) on 11 May 2014 .
- Benjamin B. Fisher, Leon Theremin - CIA Nemesis
CIA historical article on Theremin. Date unknown, but probably mid-2002.
Partly declassified on 28 December 2010.
- IW Conrad to Mr. Harbo, Security survey of the White House
8 May 1953. Partly released under the FOIA on 3 September 2010.
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© Crypto Museum. Created: Friday 18 September 2015. Last changed: Friday, 10 March 2017 - 17:14 CET.