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Cold War
Mk. 123
Clandestine transceiver

The Mk.123 was a highly compact valve-based self-contained spy radio set, for use by the UK's paramilitary, clandestine and diplomatic services. It was designed by Steve Dorman of the Special Communications Unit at HMGCC (GCHQ) and was introduced in 1955 as a post-war replacement for the ageing Type 3 Mk.II (B2), Type A Mk.III (A3) and other WWII 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 output 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
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The canvas carrying case
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Clear view of the transceiver inside the canvas case
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Frontal view of the transceiver. In the front some of the accessories.
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Some of the accessories supplied with the MK.123

Iranian Revolution
5 November 1978

It is often thought that, apart from espionage, the Cold War spy radio sets of the West-European Countries were never really used in the course of an actual (international) 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 its use during the run-up to the Iranian Revolution 1 [8]. Courtesy David White [1].

In October 1977 a campaign of civil resistance of a religious nature commenced against the Shah, then the leader of Persia 2 , with the intent to overthrow him and change the country into an islamic republic under Ayatollah Khomeini [8].

The hostilities intensified during the following year (1978), with strikes and demonstrations paralyzing the country from August onwards. On 5 November 1978, the demonstrations at the University of Tehran became deadly after a fight broke out with armed soldiers. Within hours, Tehran became the scene of a full-scale riot.
Riots in the streets of Teheran (Iran) on 5 November 1978. Copyright Getty Images.

Block after block of Western symbols, such as movie theaters and department stores, as well as government and police buildings, were seized, looted and burned, and the British Embassy would undergo the same fate later that day.

After the main power and all telephone lines to the embassy were cut, a group of 300 women in burkas, stormed the building and set it on fire, leaving the embassy personnel trapped inside, unable to inform the world in the usual way [3].
Shattered window of the UK Embassy in Iran on 5 November 1978. Copyright Getty Images.

Luckily one of the embassy technicians was able to retrieve his portable Mk.123 spy radio station, which was hidden away from the embassy in a secret location. After picking it up, he used the radio to contact Darwin in the Northern Territory of Australia on the emergency calling system, using morse code signals to send and OTP encrypted message. Upon receiving the message, the British government took the necessary steps to stop this illegal activity through diplomacy.

This day became known internationally as The Day Tehran Burned. Although the US Embassy narrowly escaped demolition during that day, they would eventually undergo the same fate as the British a year later on 4 November 1979.

Following the admission of the exiled and dying Shah in the United States in late October 1979, a group of youthful islamists invaded the embassy compound and seized 52 members of its staff, demanding the Shah's return to Iran for a trial.

Only six American diplomats evaded capture, hiding at the home of the Canadian ambassador before their spectacular escape back to the US. 3

The Shah had already left the US in December 1979 and was granted asylum in Egypt, where he died from complications of cancer on 27 July 1980. In September, Iraq invaded Iran, marking the beginning of the Iran-Iraq War. Following these events, the Iranian Government entered into negotiations with the US, with Algiers acting as mediator. Eventually, the hostages were released on 19 January 1981, after being held at the US Embassy in Tehran for no less than 444 days.

  1. The Iranian Revolution is also known as the Islamic Revolution [8].
  2. Persia was the name of Iran before the Iranian Revolution.
  3. In a joint Canadian/CIA covert operation, known as the Canadian Caper, the 6 US diplomats were smuggled out of the country with fake Canadian passports, under the cover of a (fake) Canadian film crew. This story was the basis for the fictional movie Argo (2012).

Serial numbers
  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.

  8. Wikipedia, Iranian Revolution
    Retrieved August 2015.

  9. Wikipedia, Iran hostage crisis
    Retrieved August 2015.
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Crypto Museum. Created: Tuesday 06 October 2009. Last changed: Wednesday, 28 February 2018 - 23:33 CET.
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