It appeared to start on the US Air Force High-Frequency Global Communications System (HF-GCS). Nothing is particularly remarkable about the stations that appear at various intervals with rotating tactical call signs of 2 or 3 syllables that change daily. These are several multi-service air-ground activities relating to command control, often involving the US Strategic Command.
What originally got the attention of people who make a hobby out of logging such things was a sudden enormous increase in the number and length of Emergency Action Messages (EAMs). Despite their important-sounding name, and high traffic priority, these are actually routine, encrypted broadcasts of updated instructions (or lack thereof) for US military assets worldwide. They use frequencies pretty much from DC to daylight. Presumably, in a real national emergency, the content would be very very much less routine.
At 0100 UTC on June 26, Jeff Haverlah logged CORN SNOW broadcasting two EAMs simulcast on the HF-GCS frequencies of 4725, 8992, and 11175 kHz USB. Two-letter tactical calls beginning in CORN are believed to be linked with the Nightwatch net, a Stratcomm airborne command post mission using multiple aircraft and ground stations. Past loggings include, but are not limited to, CORN BEEF, CORN OIL, and CORN STOCK.
Meanwhile, John, KC2HMZ, noted this net becoming very active on 11175, with two longer EAMs than the ones at 0100, a standby for traffic, and generally more net chatter than you usually get from these units. He heard the callsign as CORN ROW. Some new players appeared, using standard NATO trigraph callsigns, a type of tactical ID used by US Navy in some operations.
Here's where it gets interesting. At 0125, Jeff notes that 7703.0 kHz USB suddenly lit up with FOXTROT ZERO SIERRA (a Navy trigraph) with four different message broadcasts. 3 of these were EAMs, and the fourth was in a very rare format mostly heard in the runup to "Y2K" (remember that one?). This is a 30-character string beginning in 888800.
Jeff's guess on the content of this string is as follows:
I suspect that 25[india]600 is actually 251600, and I further
suspect that 1600z on 25 UTC was the start of this current event on HF
(12 Noon US Eeastern Time).
This took until 0135, at which time KILO TWO YANKEE came up to repeat the three EAMs (not the other string).
As if this traffic was not interesting enough to people who follow such things, an unknown station pretty much simultaneously (around 0120) broadcast a remarkably long 174-character EAM on 15016 kHz, another HF-GCS frequency.
As mentioned, we deal in radio waves. However, other people, who speculate about other things, have been burning up the Internet with ideas regarding any possible meaning of an EAM of such an extreme length. A typical report appeared July 7th, in an online Pentagon affairs column named Inside the Ring, by Bill Gertz:
The messages sent June 26 included 174 characters, much longer than normal 30-character messages, and amateur radio monitors say they have not seen the size of this message since the 1991 Persian Gulf War.
This is quite a startling claim, but I'm not sure about it. I'll have to research my old logs. (See, this is one reason we publish these...) I remember some other long EAMs, but how long will have to be checked out. This is something Utility World is good at, so I'll do it. [UPDATE 17/0610 UTC: There is indeed a monthly activity that has consistently generated long, or longer, EAMs in 2007.]
In any event, the July 13 column contains further interesting speculation:
Many who wrote suspected that the messages may have something to do with military plans for Iran and the Persian Gulf region, where three U.S. aircraft carrier battle groups are stationed.
One reader said the June 26 message traffic on Air Force Global High Frequency System networks to bases around the world was part of a major Joint Chiefs of Staff strategic "connectivity exercise" code-named Polo Hat.
... Exercises in the past have generated messages that are up to 150 characters, so the recent ones that had 174 characters or more should not be considered unusual.
Either of these two guesses would seem reasonable, were we to even attempt speculation concerning military affairs in the scariest world situation since the Cold War. Meanwhile, back in the Utility World, the combination of the long EAM with the rare Navy format simply remains an interesting, unexplained radio event.