Number Stations - Secret Signals
If you’ve ever ventured outside the shortwave broadcast and ham radio bands and tuned around the areas allotted to so-called “fixed” stations you may have heard voices reading out long lists of numbers in either four or five digit groups. These transmissions are generally called “numbers stations” and appear in a variety of languages. Transmissions in Spanish are heard most often in the United States but, in Europe, German, English and French, as well as a variety of Slavic languages are the most commonly heard.
What are they? Finding the answer to this question is not an easy task. For a start, none of these stations operates “legally”. And, with two exceptions, no callsigns are used. Consulting frequency listings does no good either since the publications that do list such stations give their origins as “unknown”. Relatively few people in the radio industry know about these stations, as this item from a recent issue of the British publication Shortwave Magazine shows: A letter from a Mr. B. Greater recalls the days in the early 1960’s when Greater, then a teen, used to enjoy receiving and decoding weather reports. These transmissions are sent over shortwave in a format not unlike that used by the number stations. But he couldn’t decode the data being sent in what he assumed were weather transmissions so he wrote to the meteorological office to ask where he was going wrong. The reply, from the senior signals officer, said the transmissions were German river soundings being transmitted in voice format from automated equipment! Other explanations suggested over the years include coded information for drug smugglers, lottery numbers, weather data, commodity prices and so on.
The most likely explanation is that these transmissions are coded messages sent to espionage agents. In various spy cases over the years agents have been caught in possession of certain items of “tradecraft”. These have included shortwave radios, microdots , invisible ink and the so-called “one-time” pad. This pad consists of a number of pages of randomly generated four or five figure groups. The pages are made of a special material that can be easily destroyed by burning or perhaps even eating. As the name suggests, each piece of paper is used only once. When the station broadcasts it usually sends a numerical identifier to single out the page of the pad to be used for that particular message. When the message has been sent the recipient subtracts the number sent over the air from the corresponding number on the sheet (or vice-versa). This is the key to the pad’s security. Without the particular sheet in question the message is unbreakable. Other methods of encryption could include the use of a book available to both sender and recipient, with a code to indicate individual words on a page. For example, “312 02″ would denote the second word on page 312. It has been suggested that one particular station that has a 3/2 figure format may be using this system. It has been noted that some stations send the same numbers up to a year apart -in one case even two years. This might suggest that practice traffic is being sent to agents for training purposes. Also, stations could be transmitting “disinformation” and time-wasting traffic to try and bog down the electronic eavesdropping efforts of an opposing intelligence service.
Whatever the real explanation, a shroud of mystery surrounds these stations and only rarely is one allowed a glimpse into this shady world. One such occasion was during the trial of British spy Geoffrey Prime. It was revealed that Prime received his instructions via shortwave radio. His traffic was encoded in five figure groups and sent over the air in Morse code. This type of revelation is rare however and one can only guess at the full story behind these mysterious and fascinating broadcasts.