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WWII
UK
SOE
  
B2 →
  
Type A Mk. III   A3
Suitcase spy radio set

Type A Mark III 1 was a small spy radio set, manufactured by the Marconi Company in the UK in 1944, close towards the end of WWII. It was intended for clandestine operations on occupied territory, by agents, special forces and resistance units. The transceiver came as a replacement for the rather bulky Type 3 Mk.II (B2) and is also known by its SOE-designator Type 21 Mk.III.

The Type A Mk.III is in fact a much smaller radio set that could easily be fitted inside a child's suitcase. It was supplied either in a fiberboard case, together with a 'spares' box, or in two water-tight containers (further explained below).

The image on the right shows a bare Type A Mk.III unit. One of its typical design features is the thumb-operated tuning wheel at the front right. Although the design of the Type A Mk.III is quite different from its predecessors, the Type A Mk.II and the Type H15a, it was clearly conceived by the same design team at the Marconi Co. [1].
  

The unit has a built-in transformer, allowing it to be powered directly from the AC mains (100-130V or 200-250V, 40-60Hz), using the fixed red/black cable at the top left. At the end of the mains cable are two banana-type plugs with exchangeable pins, allowing the radio to be used virtually anywhere in the world. Alternatively, the radio could be powered by an external 6V DC source (e.g. a car battery) by using the optional vibrator pack. The vibrator pack was connected to the 5-pin socket at the front panel and was usually only supplied with the container version.

The receiver roughly covers all frequencies between 3 and 9 MHz, divided over two ranges (blue and red) and has an intermediate frequency (IF) of 1.2 MHz. The transmitter has a maximum power output of 5W. The case is perforated at all sides, including the front panel, in order to provide sufficient cooling when in operation. When building the transceiver inside a suitcase or a metal container, care has to be taken to maintain sufficient ventilation. A nice article about the A Mk. III (A3), written by Wim Kramer in 1991 (Dutch) is available for download below [2].

  1. Also referred to as Model A Mark III and, more commonly, as A3.

Type A Mark III (A3)
Control panel - frontal view
Tuning dials
Tuning dials
Front panel detail - bottom left
Front panel detail - top right
Front panel detail - top left (power section)
Bottom view
A
×
A
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Type A Mark III (A3)
A
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Control panel - frontal view
A
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Tuning dials
A
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Tuning dials
A
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Front panel detail - bottom left
A
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Front panel detail - top right
A
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Front panel detail - top left (power section)
A
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Bottom view

Suitcase version
The most common packaging arrangement for the Type A Mk.III was a standard fibreboard child's suitcase, such as the one shown below. Although the radio was initially supplied in a slimline red suitcase, this was often swapped for an alternative one, as it was easily recognised by the enemy.

To the left of the transceiver was space for the SPARES-box which was usually stored on its side. In many cases this SPARES-box was lost and the accessories, the headphones and the morse key were simply stored aside the radio.

The lid of the case is padded with felt, with some embossed parts, so that the transceiver is well protected during transport. The image on the right shows an A3 inside an alternative suitcase. After the war, many A3 radio sets were repacked in such a case, after the original one had dried-out completely and had partly desintegrated.
  

Even during the war, the original case was often replaced for a less obtrusive one, so that an agent carrying an A3 was not immediately spotted by the enemy when travelling. In the version shown here, a crystal is inserted in the crystal socket of the transmitter (center). The crystal - and any connectors inserted in the sockets - had to be removed before the case's lid could be closed.

tcase upright, ready for transport
Suitcase
Type A Mk. III in suitcase
Type A Mk. III in suitcase, with headphones.
B
×
B
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tcase upright, ready for transport
B
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Suitcase
B
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Type A Mk. III in suitcase
B
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Type A Mk. III in suitcase, with headphones.

Container version
The Type A Mk.III was sometimes supplied in two watertight metal containers, allowing it to be dropped by parachute over occupied territory. This version was ideal for resistance groups, as it allowed the transceiver to be stored in moist places for longer period of times without problems.

The larger container, marked 'C, held the Type A Mk.III transceiver, whilst the smaller one, marked 'D', contained the SPARES-box and a vibrator pack for 6V operation. At this time we don't have a photograph of this packaging arrangement.

No image available
  

Interior
Interior seen from the bottom left
Interior seen from the bottom left
Interior seem from the top left
Interior seen from the bottom right
Interior seen from the bottom left
PSU detail
Interior detail - top right
Interior detail - bottom right - tuning section
Interior detail (7Q7 missing here)
Tuning dial
Tuning section close-up
Interior - bottom view
Front side (control panel facing down)
Rear side (control panel facing down)
Right side (control panel facing down)
Left side (control panel facing down)
C
×
C
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Interior seen from the bottom left
C
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Interior seen from the bottom left
C
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Interior seem from the top left
C
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Interior seen from the bottom right
C
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Interior seen from the bottom left
C
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PSU detail
C
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Interior detail - top right
C
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Interior detail - bottom right - tuning section
C
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Interior detail (7Q7 missing here)
C
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Tuning dial
C
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Tuning section close-up
C
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Interior - bottom view
C
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Front side (control panel facing down)
C
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Rear side (control panel facing down)
C
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Right side (control panel facing down)
C
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Left side (control panel facing down)

Technical specifications
  • Device
    Miniature suitacase spy radio set
  • Purpose
    Agent communication
  • Designator
    Type 21 Mk. III
  • Model
    Type A Mk. III (A3)
  • Frequency
    3.2-5.25 MHz (blue) and 5.2-9.55 MHz (red)
  • Valves
    7Q7, 2 x 7H7 (receiver) and 7H7, 7C5 (transmitter)
  • Receiver
    General coverage
  • IF
    1200 kHz
  • AF-output
    Low impedance headphones
  • RX modes
    AM R/T and CW
  • Transmitter
    crystal operated
  • TX mode
    CW only
  • TX output
    5W (fundamental frequency) or 3.25W (2nd harmonic)
  • Mains power
    AC 100-130V, 200-250V (40-60Hz)
  • Battery power
    6V (4.7A receive, 6.5A transmit)
Accessories
  • SPARES-box
  • Various crystals
  • Spare vibrator
  • Spare valves (7Q7, 7H7, 7C5)
  • Spare fuses
  • Spare neon indicator
  • Morse key
  • Headphones
  • Battery lead
  • Bulldog clips
  • Mains lamp socket adapter
  • Universal plugs for mains lead
  • Valve extraction tool
  • Various screwdrivers
  • Antenna (13m) and ground wire (3m) on Paxolin card
Documentation
  1. Portable Transceiver Model A MK. III Description and Operating Instructions
    Original manual with S/N 33144. 19 December 1944.
     Circuit diagram only

  2. Model A Mk. III checklist
    26 February 1945.
References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  2. Wim Kramer, De A. Mk. III
    RAM Magazine 125. October 1991. pp. 20-25. 1
  1. Reproduced here by kind permission of the author Wim Kramer.

Further information
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© Crypto Museum. Created: Sunday 20 September 2009. Last changed: Saturday, 13 July 2024 - 13:40 CET.
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