A numbers station is a shortwave radio station characterized by broadcasts of formatted numbers, which are addressed to intelligence officers operating in foreign countries. Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are also used. Stations may operate on set schedules and frequencies in the high-frequency band, while others broadcast at irregular times.
Numbers stations have been documented since at least World War I and reached peak activity during the Cold War. Several espionage prosecutions have confirmed the practice: the conviction of the Cuban Five in the United States in 2001, and the arrest of members of the Russian Illegals Program in 2010, both involved the use of shortwave number broadcasts to transmit instructions to agents. Messages are typically encrypted using a one-time pad, a method considered theoretically unbreakable when applied correctly.
Shortwave signals can propagate over intercontinental distances by reflecting off the ionosphere, allowing a single transmitter to reach agents worldwide. The receiving agent requires only an ordinary consumer shortwave radio, possession of which carries a degree of plausible deniability. These properties, combined with independence from satellite and internet infrastructure, have led analysts to argue that numbers stations retain operational relevance even in the 21st century.
Numbers stations have long been monitored by shortwave listeners, and many are known by informal nicknames based on distinctive interval signals. Hobbyist groups including ENIGMA 2000 have also developed systems for classifying identified stations.
History According to the notes of The Conet Project, which has compiled recordings of these transmissions, number stations have been reported since with the numbers transmitted in Morse code. It is reported that Archduke Anton of Austria in his youth during World War I used to listen in to their transmissions, writing them down and passing them on to the Austrian military intelligence.
Numbers stations were most abundant during the Cold War era. According to an internal Cold War-era report of the Polish Ministry of the Interior, numbers stations DCF37 (3.370 MHz) and DFD21 (4.010 MHz) were transmitted from West Germany beginning in the early 1950s.
Many stations from this era continue to broadcast and some long-time stations may have been taken over by different operators. The Czech Ministry of the Interior and the Swedish Security Service have both acknowledged the use of numbers stations by Czechoslovakia for espionage, with declassified documents proving the same. In rare cases, shortwave listeners who sent reception reports to stations that identified themselves received QSL responses, an unusual occurrence for a clandestine operation.stations KKN44, BFBX and OLX
One well-known numbers station was the E03 "Lincolnshire Poacher", which is thought to have been run by the British Secret Intelligence Service. It was first broadcast from Bletchley Park in the mid-1970s but later was broadcast from RAF Akrotiri in Cyprus. It ceased broadcasting in 2008.
In 2001, the United States tried the Cuban Five on the charge of spying for Cuba. The group had received and decoded messages that had been broadcast from the "Atención" number station in Cuba.
Atención spy case The "Atención" station of Cuba became the world's first numbers station to be officially and publicly accused of transmitting to spies. It was the centerpiece of a United States federal court espionage trial, following the arrest of the Wasp Network of Cuban spies in 1998. The U.S. prosecutors claimed the accused were writing down number codes received from Atención, using Sony hand-held shortwave receivers, and typing the numbers into laptop computers to decode spying instructions. The FBI testified that they had entered a spy's apartment in 1995, and copied the computer decryption program for the Atención numbers code. They used it to decode Atención spy messages, which the prosecutors unveiled in court.
The United States government's evidence included the following three examples of decoded Atención messages. "prioritize and continue to strengthen friendship with Joe and Dennis" "Under no circumstances should [agents] German nor Castro fly with BTTR or another organization on days 24, 25, 26 and 27." (BTTR is a CIA affiliated anti-Castro airborne group Brothers to the Rescue) "Congratulate all the female comrades for International Day of the Woman."
The moderator of an e-mail list for global numbers station hobbyists claimed that "Someone on the Spooks list had already cracked the code for a repeated transmission [from Havana to Miami] if it was received garbled." Such code-breaking may be possible if a one-time pad decoding key is used more than once. If used properly, however, the code cannot be broken.
21st century cases In 2001, Ana Belén Montes, a senior US Defense Intelligence Agency analyst, was arrested and charged with espionage. The federal prosecutors alleged that Montes was able to communicate with the Cuban Intelligence Directorate through encoded messages, with instructions being received through "encrypted shortwave transmissions from Cuba".
In 2006, Carlos Alvarez and his wife, Elsa, were arrested in Miami and charged with failing to register as agents of the Cuban government. Prosecutors said the couple admitted to using a shortwave radio and a five-digit code to communicate with Cuban intelligence.
In June 2009, the United States similarly charged Walter Kendall Myers with conspiracy to spy for Cuba, and receiving and decoding messages broadcast from a numbers station operated by the Cuban Intelligence Directorate to further that conspiracy. As discovered by the FBI up to 2010, one way that Russian agents of the Illegals Program were receiving instructions was via coded messages on shortwave radio. It has been reported that the United States has used number stations to communicate encoded information to persons in other countries. There are also claims that State Department-operated stations, such as KKN50 and KKN44, used to broadcast similar "numbers" messages or related traffic, although these radio stations have been off the air for many years.
In October 2011, Heidrun and Andreas Anschlag were arrested in Marburg, Germany, and later jailed after being found guilty of spying for Russia for over 20 years. At the time of the arrest, Heidrun was found receiving encrypted messages using a shortwave radio connected to a computer. "She was reported to have been so shocked she fell off her chair, pulling the connection cable with her."
North Korea revived number broadcasts in July 2016 after a hiatus of sixteen years, a move which some analysts speculated was psychological war; sixteen such broadcasts occurred in 2017, including unusually timed transmissions in April.
In late February 2026, coinciding with the outbreak of the 2026 Iran war and subsequent internet blackouts, a new Persian-language numbers station began broadcasting on 7910 kHz (USB). The station, designated V32 by the ENIGMA 2000 monitoring group on March 3, 2026, features a male voice reading structured numeric groups in Persian, frequently repeating the word "Tavajjoh" (Persian for "Attention"). The origin is traced to a facility inside Panzer Kaserne, a US military base in Böblingen, Germany.
Suspected use for espionage It has long been speculated, and was argued in one court case, that these stations operate as a simple and fool-proof method for government agencies to communicate with spies working undercover. According to this hypothesis, the messages must have been encrypted with a one-time pad to avoid any risk of decryption by the enemy. Writing in 2008, Wallace and Melton described how numbers stations could be used in this way for espionage:
The one-way voice link (OWVL) described a covert communications system that transmitted messages to an agent's unmodified shortwave radio using the high-frequency shortwave bands between at a predetermined time, date, and frequency contained in their communications plan. The transmissions were contained in a series of repeated random number sequences and could only be deciphered using the agent's one-time pad. If proper tradecraft was practised and instructions were precisely followed, an OWVL transmission was considered unbreakable. As long as the agent's cover could justify possessing a shortwave radio and he was not under technical surveillance, high-frequency OWVL was a secure and preferred system for the CIA during the Cold War.
Evidence to support this theory includes the fact that numbers stations have changed details of their broadcasts or produced special, nonscheduled broadcasts coincident with extraordinary political events, such as the attempted coup of August 1991 in the Soviet Union.
A 1998 article in The Daily Telegraph quoted a spokesperson for the Department of Trade and Industry (the government department that, at that time, regulated radio broadcasting in the United Kingdom) as saying "These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption."
Formats
Generally, numbers stations follow a basic format, although there are many differences in details between stations. Transmissions usually begin on the hour or half-hour.
The prelude, introduction, or call-up of a transmission (from which stations' informal nicknames are often derived) includes some kind of identifier, for the station itself, the intended recipient, or both. This can take the form of numeric or radio-alphabet "code names" (e.g. "Charlie India Oscar", "250 250 250", "Six-Niner-Zero-Oblique-Five-Four"), characteristic phrases (e.g. "¡Atención!", "Achtung!", "Ready? Ready?", "1234567890"), and sometimes musical or electronic sounds (e.g. "The Lincolnshire Poacher", "Magnetic Fields"). Sometimes, as in the case of radio-alphabet stations, the prelude can also signify the nature or priority of the message to follow (e.g., it may indicate that no message follows). Often the prelude repeats for a period before the body of the message begins.
After the prelude, there is usually an announcement of the number of number-groups in the message, the page to be used from the one-time pad, or other pertinent information. The groups are then recited. Groups are usually either four or five digits or radio-alphabet letters. The groups are typically repeated, either by reading each group twice or by repeating the entire message as a whole.
Some stations send more than one message during a transmission. In this case, some or all of the above process is repeated, with different contents.
Finally, after all the messages have been sent, the station will sign off in some characteristic fashion. Usually, it will simply be some form of the word "end" in whatever language the station uses (e.g., "End of message; End of transmission", "Ende", "Fini", "Final", "конец"). Some stations, especially those thought to originate from the former Soviet Union, end with a series of zeros, e.g., "00000" "000 000"; others end with music or other sounds.
Because of the secretive nature of the messages, the cryptographic function employed by particular stations is not publicly known, except in one (or possibly two) cases. It is assumed that most stations use a one-time pad that would make the contents of these number groups indistinguishable from randomly generated numbers or digits. In one confirmed case, West Germany did use a one-time pad for numbers transmissions.
Transmission technology