Note (2023/02/06): For listening, use the internet SDR based HFGCS list You just pick a frequency and receiver site, which open an internet SDR configured and tuned. I fixed the broken links to EAM recordings on this page. I also have set up a BIG collection of EAMs in my Playlist of Military Radio Comms.
Of all of the aeronautical communications one may find while tuning the radio spectrum, there is one genre that is simultaneously fascinating, mysterious, and eerie. It is the phonetically encoded, highly cryptic messages heard at intervals on specific HF and VHF frequencies. Known as "Emergency Action Messages" (EAMs), they are warfighting instructions to the United States nuclear forces. As practitioners of nuclear warfare, these forces constantly train drill with the intention of making no mistakes with devices that are "shatterers of worlds." If you listen to their frequencies, you will hear both training and messages designed to defeat the use of "traffic analysis" by adversarial radio intercept operators.
EAMs are recognized by their format: a six character preamble (repeated once) followed by "STAND BY...MESSAGE FOLLOWS." Then one hears a long string of phonetic codes, spoken at a cadence of one character per second. The airborne radio operators often have plenty of background noise getting into their microphones, while the ground based relays often have have an other worldly echo and a strange "ticking" sound on their audio. Some are extremely long, extending into the hundreds of letters! Is it possible that these are operational mesages, or a practical test for operator proficiency? That will certainly remain a mystery because USSTRATCOM says very little on the subject of its work.
Skyking messages (not heard since late 2019) are much shorter, and characterized by the preamble, "SKYKING SKYKING DO NOT ANSWER. MESSAGE FOLLOWS..." One then hears a short string of characters followed by an authentication code.
Is it possible to decrypt an EAM? Not in a trillion years; not with any supercomputer - they use unbreakable "one time keys" which are quite random and never repeating.
The Navy's TACAMO fleet consists of 16 E-6B aircraft and provides a survivable communications link between national decision-makers and the country's arsenal of strategic nuclear weapons. It was first flown diring the Cold War era and functions not only as a communications relay but also host to commanders involved in directing post-doomsday military action action against an adversary.
E-6B aircraft are derived from the Boeing 707, with modifications designed to enhance its effectiveness. It bristles with antennas, covering the spectrum from "DC to daylight." At the low end, there are several thousand feet of antenna wire, on a reel, for communications with submarines on VLF. At the high end, EHF antennas enable very broadband communications through satellites and terrestrial links. They are in essence, flying repeaters with "store and foreward" capabilities. An E-6B can stay aloft for 15 hours without refueling, and up to 72 hours with periodic visits from tankers. TACAMO aircraft are based at Offut Air Force Base, Nebraska, Patuxent Naval Air Station, Maryland, and Travis Air Force Base, California. When aloft, they go out "someplace" and practice various nuclear war scenarios.
The US Air Force, on the other hand, operates E-4B National Airborne Operations Center (NAOC) aircraft. Its mission is to maintain military and civil functions after the destruction of conventional national leadership. Staff on board the plane, in the event of a loss of the Pentagon, White House, Congress, and commands on military bases, will send commands unleashing retaliatory action on an adversary anywhere on the planet. Based at Offut AFB, an E4B is always on alert and available for service to the President, Secretary of Defense, the Joint Chiefs of Staff.
The NAOC is based on the Boeing 747-200, and is outfitted with a wide variety of staff and equipment necessary to communicate globally with military forces and continue government operations after a nuclear attack on the United States. It can carry a staff of 112 persons, and can stay aloft for times comparable to the TACAMO aircraft mentioned above. E4Bs bristle with similar antennas to the E-6B, and have no real limits on their communications spectrum. A NAOC can go to any radio frequency and transmit a blistering level of RF.
Generally, one can hear EAM transmissions on the main Global High Frequency Communications System frequencies. Three other HF frequencies are often used for airborne relays, and these aircraft have also been heard on the military aeronautical UHF band. HF frequencies include:
Units are in MHz and include both Nightwatch and Mystic Star networks... Primaries: 4.724, 8.992, 11.175, 15.016 Secondaries: 5.702, 6.739, 6.697, 8.036, 8.053, 8.083, 8.776, 9.212, 11.155, 11.159, 11.244, 13.155.
Thomas P. M. Barnett, a well known expert on the large scale military affairs, asserts that great-power warfare is unlikely to ever occur between nuclear powers. Core industrialized countries are becoming more economically intertwined and less likely to engage in ultimately self-destructive campaigns against trading partners. Such populations of people tend to favor peaceful engagement with others who share economic and political similarities. Therefore it is possible that the nuclear strike forces responsible for EAMs will practice their doomsday scenarios indefinitely. At the same time, conventional forces will shift focus to less observable operations against rogue regimes and adversaries who are unresponsive to deterrence. That means conflicts will often be fought covertly by special operations forces.