Operation RAFTER
RAFTER was a code name
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...

 for the MI5
The Security Service, commonly known as MI5 , is the United Kingdom's internal counter-intelligence and security agency and is part of its core intelligence machinery alongside the Secret Intelligence Service focused on foreign threats, Government Communications Headquarters and the Defence...

 radio receiver detection technique, mostly used against clandestine
Clandestine operation
A clandestine operation is an intelligence or military operation carried out in such a way that the operation goes unnoticed.The United States Department of Defense Dictionary of Military and Associated Terms defines "clandestine operation" as "An operation sponsored or conducted by governmental...

 Soviet agents and monitoring of domestic radio transmissions by foreign embassy personnel from the 1950s on.


Since most radio receivers are of the superhet design, they typically contain local oscillator
Local oscillator
A local oscillator is an electronic device used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency conversion, also referred to as heterodyning, produces the sum and difference frequencies of the...

s which generate a radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 signal in the range of 455 kHz above or sometimes below the frequency to be received. There is always some radiation from such receivers, and in the initial stages of RAFTER, MI5 simply attempted to locate clandestine receivers based on picking up the superhet signal with a quiet sensitive receiver that was custom built. This was not always easy because of the increasing number of domestic radios and televisions in people's homes.

By accident, one such receiver for MI5 mobile radio transmissions was being monitored when a passing transmitter produced a powerful signal. This overloaded the receiver, producing an audible change in the received signal. Quickly the agency realized that they could identify the actual frequency being monitored if they produced their own transmissions and listened for the change in the superhet tone.

Soviet transmitters

Since Soviet short-wave transmitters were extensively used to broadcast messages to clandestine agents, the transmissions consisting simply of number sequences read aloud and decoded using a one-time pad
One-time pad
In cryptography, the one-time pad is a type of encryption, which has been proven to be impossible to crack if used correctly. Each bit or character from the plaintext is encrypted by a modular addition with a bit or character from a secret random key of the same length as the plaintext, resulting...

, it was realized that this new technique could be used to track down such agents. Specially equipped aircraft would fly over urban areas at times when the Soviets were transmitting, and attempt to locate receivers tuned to the Soviet transmissions.


Like many secret technologies, RAFTER's use was attended by the fear of over-use, alerting the quarry and causing a shift in tactics which would neutralize the technology. As a technical means of intelligence, it was also not well supported by the more traditional factions in MI5. Its part in the successes and failures of MI5 at the time is not entirely known.

In his book Spycatcher
Spycatcher: The Candid Autobiography of a Senior Intelligence Officer , is a book written by Peter Wright, former MI5 officer and Assistant Director, and co-author Paul Greengrass. It was published first in Australia...

, MI5 officer Peter Wright
Peter Wright
Peter Maurice Wright was an English scientist and former MI5 counterintelligence officer, noted for writing the controversial book Spycatcher, which became an international bestseller with sales of over two million copies...

related one incident in which a mobile RAFTER unit in a van, or panel truck, was driven around the backstreets in an attempt to locate a receiver. What with interference and the effects of large metal objects in the surroundings, such as lamp posts, this proved futile. Later, however, they concluded that the receiver itself had been mobile, and may at one point have been parked next to the van, hidden by a high fence.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.