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Mk. 123
Clandestine transceiver

The Mk.123 was a highly compact valve-based self-contained transceiver, for use by the paramilitary, clandestine and diplomatic services. It was designed by Steve Dorman of the Special Communications Unit at HMGCC (GCHQ). It was introduced in 1955 as a post-war replacement for the ageing Type 3 Mk.II (B2), the later A3 and other war-time clandestine radio stations.
Dorman started development of the Mk.123 in 1947, but the set wasn't released until 1955, when the first 300 units were released to the Diplomatic Wireless Service at Hanslope Park (UK). Shortly afterwards, another 200 units were issued to the S.A.S. and the final 485 units were deliverd to the MI-6 headquarters in London.

The Mk.123 was shipped either in a grey wooden transit box or in a green canvas carrying case. The one shown here came in the canvas case and has serial number (123860), indicating that it was used by MI-6.

The radio set is housed in a rather small grey-painted metal case and can be connected directly to a variety of mains voltages (AC). Internally, it consists of three building blocks: the the power supply unit (PSU) in the middle, the receiver to the left of it and the transmitter at the right. The three units are mounted on an aluminium base plate and are connected together with a series of plugs and sockets, making it a very serviceable device.

The receiver has a sensitivy of 1µV (at 10dB S/N) and produces 0.3 mW audio ouput into 10K headphones. The IF is at 465 kHz [2]. Both the transmitter and the receiver operate between 2.5 and 20 MHz, divided over three ranges:
  • 2.5 - 5MHz
  • 5 - 10 MHz
  • 10 - 20 MHz
The crystal-driven transmitter is suitable for CW (morse) only and can be hand-keyed using the built-in morse key (front/right corner) or an external key, at speeds up to 40 words per minute (wpm).
The canvas carrying case Clear view of the transceiver inside the canvas case Frontal view of the transceiver. In the front some of the accessories. Some of the accessories supplied with the MK.123

Mk. 123 in use
It is often thought that Cold War spy radio sets were never really used in action (i.e. during an actual conflict). With regards to the Mk.123 this is not true, as the set was in fact used in a series of international incidents. One example is the story below (courtesy David White) [1].
It happened in Teheran (Iran) on 5 Nov 1978. A group of 300 woman, wearing burkas, stormed the British embassy and set it on fire [3]. Shortly before the incident, all power and telephone lines to the embassy had been cut by the Iranians, so that the personel was trapped inside the building and couldn't inform the world.

Luckily one of the operators was able to retrieve his Mk.123 spy set, which was hidden away from the embassy. After picking it up, he used the Mk.123 to contact Darwin in the Northern Territory of Australia on the emergency calling system, using encrypted morse code signals.

The British government could then take the necessary steps through diplomatic channels, in order to stop this illegal activity. The image above show a similar indicent that happened a few weeks later when the US Embassy was attacked and 53 people were taken hostage.
  1. Personal correspondence with David White (Hut 1: Diplomatic Wireless Service)
    Former MI-6 technician who worked at Hanslope Park.

  2. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  3. BBC newscast of 5 November 1978
    Audio/video clip about the events on 5 November 1978 from the BBC archives.

  4. Original Manual, Mk. 123 Transmitter/Receiver
    Technical Publication No. 82. Declassified 1996.

  5. June Stirrat, The Mk 123 Spyset
    Short Wave Magazine. October 1992. pp. 39-41.

  6. Ben Nock (G4BXD), The Mk.123 'Spy' set
    Radio Bygones, June/July 1994. pp. 18-23.

  7. Steve Dorman & Pat Hawker, The Mk.123 'Spy-Set' - A follow-up
    Radio Bygones, August/September 1994. pp. 25-27.

Further information

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