Emergency Action Message (EAM) transmissions are associated with the High Frequency Global Communications System (HFGCS). The HFGCS is a network of single sideband transmitters used by the United States Air Force to transmit encrypted messages to in-flight military aircraft, ground stations and in some cases, US Navy surface vessels. The purpose and format of the messages are subject to wide-ranging speculation, but are generally thought to be for directing nuclear-capable forces regarding the execution of specific attack options.
Recorded by John Lutz, courtesy of the Shortwave Radio Archive.
Part of the Shortwave Transmissions project, documenting and reimagining the sounds of shortwave radio - find out more and see the whole project at https://citiesandmemory.com/shortwave
