Individual countries or specific regions may be included or withheld in the EAM, as specified in the Single Integrated Operational Plan (SIOP).
[3] EAMs use cryptographic protocols (including such methods as digital signatures) to authenticate the messages,[1] thereby ensuring that they cannot be forged or altered.
In the United States, the EAM will be issued from the National Military Command Center (NMCC) at the Pentagon or, if it has been destroyed by an enemy first strike, by the Alternate National Military Command Center - Site R at Raven Rock, Pennsylvania or by the U.S. Air Force E-4B Nightwatch aircraft/U.S.
The messages are then relayed to aircraft that are on alert by the U.S. Strategic Command at Offutt Air Force Base in Omaha, Nebraska, via single-sideband modulation radio transmitters of the High Frequency Global Communications System (formerly known as the Global High Frequency System).
The start of a Sky King headed EAM message is briefly heard on the cockpit radio when the bomber crew are scrambled in the feature film By Dawn's Early Light.