Tim Benjamin

What could be more innocent than a cab driver, casually listening to his short-wave radio? It’s perfectly plausible. But what if the “cab driver” is working for a foreign intelligence agency, and what if his short-wave radio is picking up something altogether more sinister than the latest news from home?

If you scan carefully through the short-wave spectrum, chances are that from time to time you will come across a peculiar, disembodied voice reading out and repeating sequences of numbers and letters, for hours on end. The voices usually read in English, often with a heavy accent, but may sometimes read in German, Russian, or another language. Sometimes there is no voice at all, but instead electronic noises resembling Morse code, or other, more bizarre patterns of bleeps and pops. Collectively, these radio transmissions are known as “Numbers Stations”, and members of the public have gathered online to catalogue, record, and attempt to decode these broadcasts.

It should be made clear that these Numbers Stations are not shipping or weather bulletins; furthermore they are not licensed in any usual sense, and information on them is difficult to find from the government agencies responsible for radio use and misuse. Numbers Stations have been reported since the First World War, making them among the earliest radio broadcasts, and although not acknowledged in general by government agencies, the UK’s GCHQ have stated: “GCHQ are aware of the existence of Numbers Stations but cannot comment on operational matters”. It is, however, illegal to listen to Numbers Stations in the UK.

A typical Numbers Station broadcast will begin at the top of the hour, or a whole number of minutes after the hour, with some form of announcement: a single letter repeatedly keyed in Morse, or a piece of music played for several minutes. There then follows a voice, which usually begins with a three-digit number, and a call to attention (literally, the word “Attention”, or perhaps with a bell or gong). The main message will then begin, consisting of a count of the number of elements in each part of the message — which will be grouped into short sequences of four or five letters or numbers — and then the message-part itself. The groups will usually be repeated many times, until the end of the message, signalled either by the word “End”, or by a repeat of the announcement music or tones. Each of the Stations is unique; the one thing that binds them together is the extreme length of time that the broadcasts are on the air.

By triangulation, it has been possible to demonstrate the origins of some Numbers Stations broadcasts: for example, antenna farms on US government property in London, or from within British military bases in Cyprus. Increased activity and changed broadcasts on Numbers Stations have coincided with dramatic political events — for example, the attempted “August Coup” against Mikhail Gorbachev in the Soviet Union, in 1991.

Some have speculated that the World Wide Web offers new opportunities to those broadcasting Numbers Stations. One frequently finds, for example, apparently random sequences of numbers and letters posted onto little-used blogs and forums; although it is potentially straightforward to identify the source of the message (although spammers have shown that it is easy to mask your identity online) it is not the source that is important - an agent in the field can innocently visit an internet café and visit her favourite blog, or login to his favourite forum...

Numbers Stations are potentially a very useful espionage tool. Although it is relatively straightforward — for example by triangulation — to discover the source of a broadcast, it is impossible to know who is tuning in, without catching the receiver red-handed. And even if you did: what could be more innocent than a cab driver, casually listening to his short-wave radio?