There are two kinds of dedicated radio listeners. Most are those who listen regularly to their FM or AM station of choice, or to a station that only broadcasts on the internet. The rest are dedicated to other frequency scales: high frequency (also known as shortwave), followed by very high frequency and, after that, the ultra high frequency range, which includes police scanner talk and even satellite signals. Shortwave listeners encounter a world of mostly international radio stations broadcasting from countries like China, Cuba, Iran, or Romania. These frequencies also include amateur radio and marine and air traffic.

Sooner or later, however, those who listen to these more off-beat signals will stumble across strange broadcasts repeating number groups in digitally synthesized voices. Sometimes they are read live, sometimes in Morse code, and sometimes by means of digital noise transmission. These are the so-called numbers stations.

Numbers stations have been in existence since World War I. Over the years they have attracted sporadic interest from journalists, video game designers, and filmmakers. Despite this attention, there are few explanations of what these signals actually are. Too often, they are described as “spooky,” “creepy,” or “mysterious,” and the discussion stops there. It may be disappointing to some, but these stations are not signals from aliens or mind control devices, nor are they dead relics of the Cold War — rather, these stations are part of the sophisticated work of intelligence agencies and militaries, and they are very much still on the air. This article will explain what they are, how to listen to them, and why they matter.

What Are Numbers Stations and Why Are They Used?

Cryptography, the science of encrypting text and data, has been around since the times of Caesar. Before the invention of radio, secret messages could be conveyed in coded letters or through light signals. In the 19th century, transmission along electric lines became possible, first with the telegraph and then with the telephone. Radio was invented at the turn of the century and was quickly put to military use, as the world learned when German interception of the Russian Army’s transmission of orders “in the clear” helped the Germans win a crushing victory in East Prussia in 1914.

The first use of coded numbers broadcasts was during the last years of World War I, when they were sent in Morse code in Low and Medium wave frequencies. Shortwave came into use in the early 1920s and has been used to send encrypted messages since then. When directed at the ionosphere at an angle, shortwave signals reflect back down to Earth at great distances beyond the horizon. This is handy for intelligence operations in foreign countries, or for the military to send orders to faraway units.

But if these signals can be heard all over the world, then, of course, the messages must be encrypted. This is where one-time pads come in. The one-time pad, the only mathematically unbreakable encryption system, is usually a sheet of paper with random numbers in groups of five or more digits. Typically, the letters of the message are converted into numbers and are added to numbers from the notepad using a simple mathematical operation known as “false addition.” The result is then transmitted. The recipient uses the same page from his own one-time pad and extracts the plain text message by applying “false subtraction” to the encrypted message.

This procedure is simple, yet highly effective: The message can only be decoded by a third party if they get access to recipients’ one-time pads. This is sometimes possible for counterintelligence, either using double agents or by arresting the recipient, most likely while he is receiving the signal. A number of events in the 20th century have proven that intelligence agencies do, in fact, use these signals.

From 1945 to 1956, the CIA and the British Secret Intelligence Service dispatched agents to support anti-Soviet guerrillas in the Baltic States, Belarus, and Ukraine. Most were captured with their radio transmitters and code books. The KGB used these codes to force captured agents to send signals back to their masters to lure more agents. In 1988, the KGB showed off these codebooks and transmitters in a TV movie called “The Game”.

When the FBI recruited a source inside the Communist Party of the United States, it observed many coded messages sent by the Soviets to U.S. communists. The bureau decoded these messages, with decoding instructions it had received from the spy that had infiltrated the KGB, as seen in publicly released FBI files about “Operation Solo.” In 1983, the KGB uncovered CIA agent Alexander Ogorodnik, a Soviet diplomat who was receiving tasking from American numbers broadcasts. Another well-known case is the 2001 “Cuban Five” case in which Cuban spies were caught and shortwave broadcasts were used in the case against them. The numbers message was sent to the spies via radio and entered into a Toshiba laptop. Then it was decoded by a special floppy disk that contained the decode key. In 2013 a German couple was put on trial for spying for Russia and giving away military secrets. They, too, had received messages from shortwave and were actually caught while receiving one. Finally, the infamous Russian spy ring of 2010 was said to use “radiograms.” (In intel or military documents, you will not encounter the term “number station;” instead it will be “radiogram,” “radio message,” or “transmission.”)

Tracking Numbers Stations

Decoding these messages is impossible without access to the one-time pads used to encrypt them. Nevertheless, for many decades people have studied them and even made accurate schedules of times of their transmissions. William (Bill) Thomas Godbey, or “Havana Moon,” first made numbers stations logging popular in the 1980s. Later, Simon Mason wrote a book called Secret Signals: The Euro Numbers. For the last two decades, much work has been done by two groups of radio listeners: Enigma 2000 and Numbers and Oddities. Enigma has set designations for these stations based on the language or digital format. E for English, S for Slavic, G for German, V for various. Two independent sites Priyom.org and numbers-stations.com, of which I am a founder, both have vast information on various numbers stations used both now and in the past. Last year, British historian Lewis Bush published a book called Shadows of the State about these stations and their possible locations. Also notable is the “Conet Project” a freely available compilation of past numbers station recordings. These people have done impressive work uncovering the owners of now-defunct numbers stations using documentary evidence, and have pinpointed the owners of modern day stations using technical observations like signal triangulation and other methods.

Numbers stations were most active starting around 1960, when secret coded message stations such as The Lincolnshire Poacher, The Swedish Rhapsody, and Gongs were broadcasting. There was a drop in activity following the collapse of the Soviet Union, since many intelligence agencies using numbers stations were linked to the KGB, like the Stasi and the Romanian Securitate. For their part, many Western spy agencies started to use new means of encrypted message transmission such as steganography, which involves encrypting message in pictures or any digital media. However, numbers station monitor groups have shown that Russian foreign and military intelligence SVR and GRU still use numbers stations extensively (see S06, E06, E07, V07). Other countries that use numbers stations according to my and others’ reporting are Poland (see E11, S11a), Ukraine (S06s and E17z), Egypt, and Cuba. After a halt in activity from 2000 to 2016, North Korea has resumed broadcasting coded messages directly from its state radio — Radio Pyongyang — disguised as mathematics or physics problems for “distant university students.” The intended recipient is indicated by a song played before the transmission and an identification number given at the start of the message.

Sometimes the sponsor of a station is not as self-evident one might think. For instance, not all Russian stations transmit in Russian: sometimes they transmit in English or Spanish. Polish stations transmit in English and Russian. Usually these attributions have been made by signal triangulation and measurements of signal strength and directions.

It should also be noted that militaries use coded numbers broadcasts for other purposes — for instance, it has been proven that the well-known Russian “Buzzer” was used by the Russian military. However, this signal is solely for internal Russian use: it is not directed towards Europe and the US and is not used for spy operations. Rather, it is mainly used for sending tasks and instructions to various Russian military units within the country. This is shown in part by the fact that Russian military stations send their signals during the daytime, when, due to the behavior of the ionosphere, their messages do not propagate well to Western Europe and the United States.

It is very easy to listen to these stations. You don’t necessarily need a shortwave radio; today most radios are software-defined radios and can be listened to remotely on the internet. Because these receivers are operated by software, they can be connected online and operated remotely by people across the world. Most popular is the online based software defined radio, the so-called “WebSDR” at Twente, Netherlands. The site SDR.HU also offers various receivers across the world. Rather accurate predictions of numbers stations frequencies and broadcasts are available at Priyom.org and numbers-stations.com, my site. Numbers-Stations.com also has a popular Discord server where you can report your findings and ask questions and has quickly become one of the most prominent resources on this subject.

Conclusion

In his book Shadows of the State, Bush warned that if we don’t monitor the work of the intelligence and military —those of our own countries, as well as those of foreign nations — we risk allowing these institutions to overtake our governments. While this may sound like something of an overstatement, especially to those in the West, in Russia for instance, security agencies have gained great influence over government and state policy as authors like Andrei Soldatov have claimed. Tracking the work of these entities as subtly and accurately as possible and learning their history helps us better understand the scope of intelligence and military policy.

Numbers stations aren’t spooky, nor are they a mystery — for many in the intelligence and military communities, they are daily tasks that serve the interests of their country. We can follow their work at least partially by listening to these transmissions. If you happen to hear them you will know that, as Bush put it, the “shadows of the state” are simply doing their daily work.

CORRECTION: A previous version of this article referred to encrypting message in pictures or digital media as stenography. The practice is known as steganography.

Māris Goldmanis is a historian, co-founder and editor of numbers-station.com and an avid numbers stations researcher.

Image: Wikimedia Commons