HFGCS Messages are transmitted in plain voice and are encrypted using a one time scratch system that cannot be decrypted on the outside. There is no ability to try to decrypt these messages, however it is possible to make note of operational situations. Other messages transmitted in STANAG vocoder use encryption such as AES 256.HFGCS is the US Air Force High Frequency Global Communications System. Ground stations worldwide talk to aircraft on USB and STANAG ALE date mode. The USAF also uses this system for EAMs in some cases communications for use of the Nuclear Triad.

Voice frequencies (USB, kHz)
4724
8992
11175
15016

Main frequency is usually 11175 by day and 4724 by night.

Ground station callsigns
Mainsail: Any ground station The Network Control Station uses a one- or two-word callsign that is replaced daily at 00:00 UTC Individual stations: Andersen
Andrews
Ascension
Croughton
Diego Garcia
Elmendorf
Hickam
Lajes
Offutt
Puerto Rico
Sigonella
West Coast
Yokota

Aircraft callsigns
Reach ###: Air Mobility Command transport aircraft Doom ##, Rogue ##, Skull ##: Boeing B-52 Stratofortress The voice channels carry two-way communications with aircraft using many different callsigns. The main frequency is 11175 during the day, or 4724 during the night. The aircraft regularly enter and exit the network. To do either, the aircraft usually asks the ground station, which then authenticates the operation by giving a pre-defined three letter code, and expecting a single letter in return. Less often, the aircraft may enter in the blind, giving a two-letter authentication code directly. Authenticated nets have a higher priority and in cases means an actual operation. The HFGCS provides a phone patch service, allowing aircraft to make unclassified phone calls via the DSN. Phone patches are usually requested on the main frequency, but then moved elsewhere by the ground station to free up the channel. This is sometimes conducted using MARS operators working shift operations in different locations. In addition to two-way communications, there are several types of one-way traffic, usually transmitted on all frequencies simultaneously by all ground stations: Test count: These are made multiple times a day, and are most commonly associated with shift changes at the Network Control Station. A typical test count is broadcast as follows: "This is with a test count; testing, 1 2 3 4 5, 5 4 3 2 1; this is , out." Emergency Action Message (EAM): A very common broadcast type which consists of an encrypted string of alphanumeric characters, usually 30 characters long. A typical EAM is broadcast according to the following procedure: "All stations, all stations, this is , ." Optionally, if a message is addressed to a particular station: "For ," repeated twice. The first six characters of the message, followed by "Stand by," repeated altogether thrice. "Message follows."; alternatively, if a message is not 30 characters long: "Message of characters follows." The message in full. "I say again." The message in full. Optionally, if a message is not 30 characters long: "This complete message of characters." "This is , out."; alternatively, if there is another message to follow: "This is , more to follow, stand by." Skyking (or Foxtrot): An uncommon broadcast type which consists of a codeword, the time, and an authentication code. The codewords are names of popular rock bands and movie titles. A typical Skyking is broadcast according to the following procedure: "Skyking, skyking, do not answer." The codeword, repeated twice. "Time" followed by the minutes of the current hour, as two digits, each spelled separately. "Authentication" followed by two letters. "I say again," followed by the steps 1 to 4 repeated. "This is , out." From time to time, the operator may inform stations to disregard the last message after broadcasting it.

ALE frequencies (USB, kHz)
3137
4721
5708
6721
9025
11226
13215
15043
18003
23337

Ground station addresses
ADW: Andrews
AED: Elmendorf
CRO: Croughton
GUA: Andersen
HAW: Ascension
HIK: Hickam
ICZ: Sigonella
JDG: Diego Garcia
JNR: Puerto Rico
JTY: Yokota
MCC: West Coast
OFF: Offutt
PLA: Lajes

Aircraft addresses
1#####: Lockheed C-5 Galaxy 2#####: Boeing C-17 Globemaster III 4#####: McDonnell Douglas KC-10 Extender 5#####: Boeing KC-135 Stratotanker E3####: Boeing E-3 Sentry NW1: Boeing E-4 ("Nightwatch") Be Advised: The digits are assumed from the last digits of the tail numbers.The ALE channels are used primarily for text messaging with the 2G ALE Automatic Message Display (AMD) feature, although radio checks using plain voice are common. Each active ground station emits an ALE sounding every 3 hours.

SIPRNet Frequencies (USB)
3113
5702
6715
8968
11181
15091
17976
27870

Ground station general locations
ADWSPR: Andrews
AEDSPR: Elmendorf
CROSPR: Croughton
GUASPR: Andersen
HAWSPR: Ascension
HIKSPR: Hickam
ICZSPR: Sigonella
JDGSPR: Diego Garcia
JNRSPR: Puerto Rico
JTYSPR: Yokota
MCCSPR: West Coast
OFFSPR: Offutt
PLASPR: Lajes

SIPRNet Information
Same as the ALE network, but with the suffix DAT or IGM. The HFGCS provides an HF gateway into the SIPRNet, a U.S. Department of Defense computer network. Links are established using 2G ALE, while the data mode used is MIL-STD-188-110A.