During and since the Cold War, several shortwave radio stations have transmitted continuous voice broadcasts of apparently random numbers in numerous languages in four or five figure groups. No public statement has been made by any originating country concerning the purpose of these signals, but they have a clandestine role in communicating with agents operating in denied areas. The numbers may conceal an enciphered message, or a particular sequence broadcast at a predetermined time may convey a hidden meaning in much the way the messages personnel that accompanied the BBC news bulletins during World War II acted as a one-way channel to recipients briefed to understand the meaning of certain otherwise innocuous texts.
The broadcasts are not licensed by the International Telecommunications Union, although a Spanish four-digit channel was traced to the Central Intelligence Agency’s transmitter at Warrenton, Virginia, and Cuba is the source of similar five-figure groups. Many of the transmissions appear to be live, but some are automated, with distinctive clicks to be heard between each number. The most common languages are English, Spanish, Portuguese, German, Czech, and Chinese, and the transmissions are made in the AM mode, making them easy to receive on conventional radios. Some are sent only at particular times and on regular days, while others are almost continuous, sometimes being duplicated on two different frequencies. One of the more distinctive, transmitted from Cyprus, begins each hour with the opening notes of “The Lincolnshire Poacher” as its station identification.