The idea of listening in to other people’s wireless communications dates back to the beginning of wireless (or radio) communication itself. Thus when necessary the messages were encoded and this made it all the more desirable to find out what was being said. Just when it was first suggested that Radio Amateurs should be used for interception purposes is hard to determine and probably pre-dates this 1938 memo:

Here it must be born in mind that there was no suggestion of picking up signals from abroad, that came later, but to locate the (supposed) enemy within the UK.

This page from the meeting is an early reference to using amateurs (surprisingly a remuneration was suggested) to listen for local signals: Adrian Simpson’s report to the Director of MI5 dated 10th August 1938 (click here) can be regarded as the real starting point of the Radio Security Service (RSS).  From the outset he appreciated that interception of short wave transmissions would be very difficult unless there was a receiver within 10 miles that could detect the ground wave. He proposed the plan for a network of Voluntary Interceptors, which he predicted, would reach considerable proportions and, if possible, cover the whole country. The Radio Society of Great Britain was approached with a request to sound out trusted radio amateurs to see if listening could be arranged on a voluntary basis.  Fortunately although their transmitters had been impounded at the outbreak of war they still had their receivers and they could all read Morse Code with a particular in reading faint signals in noisy backgrounds.

Each amateur was checked on MI5 records and visited by the local police to see if there was any reason why they could not be trusted.  Before long there was quite an army of amateurs diligently searching for spies, that didn’t exist, or the suspected transmitters guiding enemy aircraft to worthwhile targets.  The amateurs were given the  title Voluntary Interceptors (VIs) and were empowered to enter premises where a suspicious transmission was found.  As they were not armed it was a wise precaution to have the company of a police officer. In time a few hundred amateurs were asked to listen on HF for anything they could not recognise as genuine commercial or military transmissions and send them in by post written on a log sheet provided, that showed date, time, frequency and what was heard.  A few experienced people in Wormwood Scrubs checked the resulting logs and notified the amateur where they were not wanted or further intercepts were required. The organisation was given the title of the Radio Security Service (RSS) but it became apparent that the reason for its existence was false and there appeared to be no reason for continuing.  Already the armed services were setting up their own stations to expand the monitoring of types of military transmissions and there was a long established de-coding department in room 40, as the department was called, in the Admiralty building.  The Post Office and the Police had radio operators routinely checking the air waves so the RSS was out of a job.

It transpired that all was not lost:  the amateurs were not put out of work by any means.  They were logging whatever was heard and among it all located some strange stations using Ham Chat but with 3 letter call signs and on top of that sending messages in 5 letter groups of code.  This was strictly forbidden for amateurs. However MI5, located in Wormwood Scrubs prison (with cells for offices) were in charge of looking at these reports (called logs sheets) where Lt. Hugh Trevor-Roper (later Lord Dacre) (click here) in concert with Cpt Gill  worked on the messages and actually managed to decipher some to discover that they were in a hand cipher that translated into German.  Moreover the translation showed that they were not ordinary signals but apparently coming from the German Secret Service (called the Abwehr) or something equivalent to our MI6 only more widespread to include other unpleasant organizations set up by the Nazis.  Bletchley Park, previously uninterested or too busy, immediately took note and required all future messages to be sent to it and strictly no more self styled de-ciphering was to take place. It became apparent that there was a lot to be uncovered about these secret transmissions and amateurs were recruited as VIs on an ever-increasing scale to cover the British Isles.  Ultimately about 1,700 were engaged on intercepting although not at one time as many were called up, some for other duties, but many to work full-time, in uniform, for the RSS. As the organisation grew it became necessary to set it on a semi-military footing with full time operators and other staff.  For details see Arkley View.

Additional background at: :http://technology.timesonline.co.uk/tol/news/tech_and_web/the_web/article7144376.ece