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UK WWII SOE A3 →
Clandestine suitcase transceiver · 1942
Type 3 Mark II, commonly referred to as B2, is a British WWII
portable clandestine transceiver, also known as a
spy radio set,
developed in 1942 by (then) Captain John Brown at SOE Station IX,
and manufactured by the Radio Communication Department of the
SOE at Stonebridge Park.
The set was issued to agents, resistance groups and special forces,
operating on occupied territory.
The official designator is Type 3 Mk. II but the radio is also known as
Type B Mk. II,
B.II and
B2.
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The B2 came in two flavours. The initial version came in an unobtrusive
leather suitcase that allowed an agent to travel inconspicuously.
This is the most well-known variant.
Later in the war it was dropped by parachute in
two water-tight containers,
that were more suitable for use by resistance groups operating in the field.
The image on the right shows the Type 3 Mk.II in its
original brown/red leather suitcase,
which can easily be recognized as it has three locks at
the front: two simple locks at the sides, and one that can be locked
with a key at the center.
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The radio set consists of three units: a receiver (RX),
a transmitter (TX)
and a Power Supply Unit (PSU),
plus a box with spares and accessories. When
mounted in the suitcase, the transmitter is located at the center top, with
the receiver mounted below it. The PSU is at the right in such a position
that the two other units can be connected to it.
The spares box is generally positioned at the left, with the Morse key
mounted on its lid. When operating the B2, the lid of the spares box should
be placed on the table, so that the Morse key can be operated.
The Type 3 Mk.II (B2) was relatively small for its day and produced
an HF output power of 20 Watts.
Nevertheless, it was too big to carry around unobtrusively
especially when travelling by public transport.
For this reason, later radios, such as the
Model A Mk. III (A3) were made much smaller,
albeit with a limited frequency range (3.2-9.55 MHz) and reduced
power output (5 Watt).
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The diagram below gives a clear view of the controls, as seen from the top.
The case has four compartments; one for each of the modules.
At the left is the spares box or accessory kit, here shown without its lid.
The spares box has two compartments: one for the spare valves and one for
the accessories. The PSU is at the right, with the AC and DC connections at
the right edge.
The two compartments at the center hold the transmitter (top) and receiver
(bottom), that both are connected to the PSU by means of a 6-pin plug.
The PSU can be powered from the AC mains or from a 6V DC source.
The headphones are connected to the socket marked PHONES L.R. at the front.
A suitable telegraph key should be connected to the socket marked KEY on
the transmitter.
The transmitter further needs a crystal at the top right
and a tank coil at the left, just below the meter. The antenna and ground
should be connected to the two screw terminals at the top left of the
transmitter. A short green wire with a banana-plug
connects the antenna to the receiver.
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The most well-known appearance of the B2 is the suitcase version, but
hardly any surviving B2 is found in its original red leather suitcase.
In fact, the B2 was delivered in a variety of different suitcases,
ranging from sturdy leather cases to simple cardboard and even wooden variants.
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The original leather case is easily recognised,
as it has three locks
rather than the usual two. In many cases, the original case was swapped
for a more common two-lock version, as it was easily recognised by the enemy.
Later in the war, cheaper cardboard suitcases were used instead.
Louis Meulstee's excellent book Wireless for the Warrior, volume 4
[1] even shows an example of a wooden carpenter's toolbox in which a B2 is
fitted.
The dimensions of the suitcase are pretty standard for the era.
The image on the right shows a B2 in a
simple cardboard suitcase.
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Another reason for the many different types of cases is that, after the
war, many container versions (see below) were converted into
suitcase versions by collectors. Even today, collectors often move the
individual parts from the containers into a suitable suitcase. Given the
fact that the dimensions of the suitcase were rather standard,
it is relatively easy to find one, even today.
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Although the suitcase version is arguably the most popular one amongst
collectors, it was by no means the most popular during the war.
Many B2 spy radio sets were brought into an occupied country, by means
of air droppings or over sea. Most suitcases would not survive such a trip.
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Furthermore, many of the radio stations were intended for use by the
resistance, in which case they often had to be stored in moist places,
such as a forest or a farm. In such cases, a suitcase was not the
most appropriate packaging.
As the war progressed, more and more sets were supplied in two water-tight
metal containers with sufficient padding to survive a dropping.
Several brackets were present at the sides of these containers, allowing
them to be attached to a parachute or to carry them at the back of
the agent by using appropriate webbing.
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The transmitter and receiver were packed together in a
container that was marked 'G'.
A second - slightly smaller - container, held the
power supply unit and the spares box. It was marked with the letter 'H'.
After removing the lids, the two
containers would be placed side-by-side and the transmitter and receiver
were connected to the power supply unit.
A nice example is in [1].
The example shown above is from the collection of Museum Jan Corver in
Budel (Netherlands). The accessory box is missing from this one, and has
been replaced by a carton box,
which is visible at the right. The marking
'G' is visible at the front of the leftmost container.
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The Type 3 Mark II (B2) was designed in 1942 by Captain 1 John Brown
at SOE Station IX, located at The Frythe 2 — a former residential private
hotel in Welwyn (UK). For security reasons, it was decided to produce the radio
sets in-house, but as the space and facilities at The Frythe were limited, the
SOE's Wireless Production Unit relocated their manufacturing process
in June 1942 to the Bontex Knitting Mills at Beresford Avenue,
Wembley (London, UK) — known as Station VII a.
The image above was taken during WWII, probably in 1942 or 1943,
and shows the B2 production line at the Bontex Knitting Mills, which became
SOE Station VIIa (7a) [4].
This facility is also known as Stonebridge Park, named after the
railway station at the end of Beresford Avenue (Wembley).
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By the end of WWII, Captain John I Brown had been promoted to Major.
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The Frythe was the name of The Frythe Residential Private Hotel in
Welwyn, that had been confiscated by the Radio Communication Division
on 26 August 1939. It was later transferred to the newly established
SOE [4].
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The transmitter is usually mounted above the receiver and is the larger
of the two. It is crystal operated, produces an RF output power of approx.
20 Watts and is suitable for CW only (Morse).
Furthermore, the full frequency coverage is divided over 4 ranges
(or actually 8),
each of which needs its own tank coil (with A and B side)
to be plugged into a 6-pin socket below the meter.
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Furthermore, the appropriate PA grid frequency needs to be selected
with the WAVEBAND switch (7 steps) and the optimum fundamental crystal
frequency with the CRYSTAL selector (6 steps).
The circuit is based on just two valves: an EL32 for the oscillator
and a 6L6 for the PA. Provisions are made to allow the crystal to be
use in fundamental, second or third harmonic mode.
The image on the right shows the transmitter after is has been taken
out of its protective casing. The flying lead is the power cord that
is normally connected to the TX-bus of the PSU.
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For the transmitter, external tank coils are used. Each coil is
suitable for a limited frequency range and
should be inserted into a 6-pin socket just below the meter.
In order to cover the entire frequency span,
four coils are supplied (L1 to L4) that each have two sides (A and B).
Besides the correct coil, the WAVEBAND selector should be used
to select the appropriate range.
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The following frequency ranges are available:
- L1-A: 3.0 - 4.0 MHz
- L1-B: 3.75 - 5.25 MHz
- L2-A: 4.5 - 6.25 MHz
- L2-B: 5.5 - 7.5 MHz
- L3-A: 6.5 - 9.0 MHz
- L3-B: 7.0 - 10.0 MHz
- L4-A: 9.0 - 13.0 MHz
- L4-B: 12.0 - 16.0 MHz
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The receiver is usually mounted below the transmitter and is the smaller
of the two. The entire coverage from 3.1 to 15.2 MHz is divided over three
ranges that are selected by the WAVEBAND-selector at the left.
To the right of the band-selector is the tuning knob that has
two wheels: one for coarse and one for fine tuning.
Above the tuning knob is the scale readout that has a
magnifying plexiglass lens over it.
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The Power Supply Unit (PSU) is normally mounted to the right of the
transmitter and receiver in such a position that the two modules can
be connected directly to the corresponding power socket at the front.
It allows the radio set to be powered from the mains and from
a 6V battery.
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The connections for the external power supply (mains and 6V) are both
at the right. The upper two pins (the thick ones) are for connection
to a 6V DC source. The (+) terminal is marked with a red dot.
The lower two pins (the thin ones) can be used for connection
to the AC mains.
In order to avoid mistakes, it is not possible to use both power sources
simultaneously. A large selector-plug is used to select between mains
and battery.
Above this selector are four selector plugs that are
used to select the appropriate mains voltage by adding the
indicated values.
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Unfortunately, the B2 needs its own non-standard proprietary
plugs, which are often missing from the surviving sets.
The 6V DC plug can easily be replaced with a domestic (mains) plug
from the 1960s and 70s. It fits nicely over the thick pins and can
safely be used, but you would need to mark the (+) terminal of the
connector, preferrably with a red dot like on the PSU itself.
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The transformer inside the PSU is suitable for virtually all mains
voltages in the world, but it is also used when powering the B2 from
a 6V DC battery, in which case a vibrator is used to convert the
6V DC voltage into an AC voltage. A spare vibrator is usually
present inside the PSU.
Unfortunately, in most original vibrators, rubber was used as an
insulating material and its sulfur vapors have often ruined the
vibrator contacts beyond repair. In such cases the original vibrator
is best replaced by a solid state version, that can easily be
(home) made from a few components.
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Caution: please note that the PSU works with high
- potentially lethal - voltages.
Be careful when connecting the set to the mains and be very careful
when touching metal parts whilst the set is connected to the mains.
You should only experiment if you know what you are doing.
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The PSU supplies the following voltages for the receiver:
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- 230V (28mA)
- 6.3V (1.2A) filaments
- -12.5V (bias)
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The following voltages are supplied to transmitter:
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- 500V (60mA)
- 230V (18mA)
- 6.3V (1.1A) filaments
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The spares kit, also known as the accessories box, is a high storage box
with a removable lid, approx. the same size as the power supply unit.
In most cases, the lid has two mounting holes for the Morse key, but with
some B2 sets, the lid had a mounting bracket for a slide-on Morse key.
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Inside the spares kit are some of the accessories and spare. In most cases,
the box is divided into two compartments: a smaller one that contains
the spare valves, and a larger one containing all the other parts,
such as the band coils, the Morse key (when in storage), spare plugs,
spare fuses, mains adapters, etc. (full list below).
Spares kits are often missing from the surviving B2 sets. Luckily,
some collectors have been able to make good looking reproduction parts
that can hardly be distinguised from the original, greatly increasing
the value of an incomplete set.
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According to the manual, the following parts should be present:
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- 4 Transmitter coils
- 1 6L6G valve
- 1 EL32 valve
- 1 7Q7 valve
- 1 7R7 valve
- 5 Fuses, 10 Amp
- 5 Fuses, 500 mA (+ 2.1 Amp fuses)
- 1 Telegraph key
- 1 Pair headphones
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- 1 Mains lead
- 1 Battery lead
- 2 Continental plug pins
- 1 Adapter 2 pin bayonet cap
- 1 Adapter Edison screw
- 1 Aerial wire (100 ft)
- 1 Earth wire (10 ft)
- 1 Screwdriver
- 1 Operating chart (in cover)
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The B2 was supplied with a variety of different Morse keys.
The most common one in the small British telegraph key shown in the image
on the right. It was usually mounted on top of the metal lid of the accessory
box (spares container).
The same one was later used with the
Type A Mark III (A3).
Other keys, such as the ones in the images below, were also used and/or
supplied with the B2 radio. Many operators had their own preference for a
specific (external key).
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The B2 originally came with a small instruction booklet that was folded
to an envelope. The booklet contains 14 extremely thin printed
pages that are slightly larger than DIN A4.
As the last page contains calibration charts, each B2 spy set came with
its own personalized manual.
The image on the right shows the Operating Instructions of the B2 with
serial number 42796 that is part of the collection of Museum Jan Corver
in Budel (Netherlands).
A high-quality scan of this extremely rare booklet is available for
download below [A].
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Device Spy radio set Purpose Clandestine (agent) communication Developer Captain John Brown (SOE) User SOE Designator Type 3 Mk. II Year 1942 Country UK AC power 97-140V and 190-250V (40-60Hz) Consumption 27W (RX) and 57W (TX) DC power 6V, 4.5A (RX) and 9.5A (TX)
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Frequency 3.1 - 15.2 MHz Sensitivity 1 - 3 µV @ 10 mW (CW) IF 470 kHz Output 50mW into 120Ω
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Type Crystal oeprated Frequency 3 - 16 MHz (4 ranges) Output 20 W (fundamental and 2nd harmonic), 16-20 W (3rd harmonic) Antenna 18 meter wire Ground 3 meter wire
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This radio set is known under the following names:
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- Type 3 Mark II
- Type 3 Mk. II
- Type B Mk. II
- B2
- B.II
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- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004
- Ken Brooks, Special Operations Executive - The B2 spy set
The VMARS Newsletter, Issue 41, pp. 8-10.
- Imperial War Museum, The interior of No 7A wireless factory
HU 56751. Part of Brown John (Major) collection.
- Derwin Gregory, Built to Resist
An assessment of the Special Operations Executive's Infrastructure in the United
Kingdom during the Second World War, 1940-1946.
University of East Anglia, 2015.
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© Crypto Museum. Created: Tuesday 06 October 2009. Last changed: Monday, 25 December 2023 - 13:23 CET.
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![The interior of No 7A wireless factory, Bontex Knitting Mills (Stonebridge Park), Beresford Avenue, Wembley (London, UK). © IWM [3].](img/IWM_HU56751.jpg)
