Emergency Action Message 8992kHz
EAMs are coded messages that would be used in the event of nuclear conflict to give commands to nuclear-capable forces.
Bombers would receive these as "go" codes.
No bombs of course have been launched (or I wouldn't be typing this), these are more or less to make sure the messages can get through, and they are sent either once or twice hourly over the HF GCS network.
Read the wiki for more:
http://en.wikipedia.org/wiki/Emergenc...
It goes for over 5 minutes, with the sign off at the end from Andrews Air Force Base.
I recorded the whole lot of it to demonstrate the format that they take.
The signal fades in and out at times, while at other times it comes in very strong.
Received in western NSW Australia.
I played around with my random wire antenna, and it seems to have worked a treat...
Not too bad for the Sangean ATS 505!