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Author Topic:   Encrypted AIS or Blue Force AIS
jimh posted 10-26-2011 07:56 AM ET (US)   Profile for jimh   Send Email to jimh  
Very recently while reading an NTSB boating accident investigation report (see Note 1 below), I came across for the first time a mention of an encrypted AIS method that was being used by law enforcement vessels. After a bit of research on encrypted AIS I found the term "Blue Force AIS" was often used in conjunction with this method.

Blue Force AIS or encrypted AIS refers to a method of vessel automatic identification system transmission in which the data about the vessel, such as its name, course, speed, and so on, is sent with encryption so that it cannot be received by standard AIS receivers. This permits vessels, particularly military or law enforcement vessels, which employ the encrypted transmission and reception equipment to track each other, but at the same time appear invisible to other vessels, that is not show up on conventional AIS equipment.

In addition to data encryption, it appears that the Blue Force AIS transponders can also use different frequencies, specifically a band of radio frequencies known as MURS, an acronym for Multi Use Radio Service. Of course, transmitting the data on a different frequency than the standard AIS insures that it will not be received by standard AIS equipment. Here are excerpts from two vendor's literature describing the encrypted AIS or Blue Force AIS capabilities of their product:


Shine Micro's second new product, the Blue Force Tracker, combines GPS, an AIS receiver, a Multi Use Radio Service (MURS) VHF receiver and a MURS secure transmitter all in a single, easy-to-install, 25-inch weather-resistant enclosure. Designed for law enforcement, USCG, harbor patrol, search-and-rescue and other agencies, this surveillance and communications system allows official users to see AIS marine traffic, yet not be seen unless authorized. The Blue Force Tracker uses a unique combination of AIS VHF radio channels and the MURS group of VHF frequencies which are reserved worldwide for two-way communications.

MURS allows for encryption of terrestrial and marine movements. Thus, the Blue Force Tracker employs the MURS frequencies for encrypted transmissions while maintaining the option to monitor public AIS marine traffic, making it a state-of-the-art tool for applications such as law enforcement, border protection and port security - officers and agents can maintain surveillance over AIS traffic while only disclosing their own locations to a specified group. Furthermore, unlike the AIS system, MURS enables encrypted short-text messaging for secure boat-to-boat and boat-to-base communication.

(See Note 2 for citation.)


Blue Forces is a common term for own units or friendly forces. The AIS 200 Blue Force is an AIS class A mobile station that offers secure communication in addition to standard AIS functionality. This means that all users of the Blue Force units can monitor each other and be monitored by AIS Base Stations prepared with Blue Force tracking capabilities which are covering the area. In secure mode this AIS mobile station will still be able to see all AIS Mobile Stations within the coverage area, without revealing own position to anyone but friendly forces. NATO STANAG 4668 is used as guidance for implementation of functionality.

(See Note 3 for citation.)

The term MURS appears to refer to a group of five VHF channels in the 151 to 155-MHz range which are available to citizens of the USA for use without a license, as long as the transmitter power is 2-watts or less, and subject to certain other restrictions. See for more details.

In the NTSB report (mentioned above), the following was quoted as being the USCG policy for operation of their AIS units:

Coast Guard AIS policy guidance, issued in August 2008 by the admiral in charge of the Eleventh Coast Guard District, stated the following with respect to the three AIS modes:

--Standard mode--The unit will perform similarly to standard commercial shipboard AIS units, broadcasting the vessel's position and information to all other AIS receivers within VHF range. This mode is recommended for increased navigation safety and overt operations.

--Disabled mode--The unit will not transmit data at all. This mode is recommended for increased operations security and covert operations.

--Restricted mode--The unit will transmit encrypted AIS data that will be available only for friendly or blue force61 units with similar encryption capabilities. This mode is recommended as the default setting for boats with AIS units.

Based on the recommended operational setting (restricted mode), boaters should not anticipate seeing USCG vessels on their AIS receivers.


1. , Section 1.15.2, Coast Guard AIS Policy. The section quotes Coast Guard directives regarding when use of encrypted AIS was appropriate.

2. is a press release from manufacturer Shine Micro, a Washington (state) based marine electronics manufacturer.

3. 97583FFE2F31AD55C1257798002E384A?OpenDocument, from Kongsberg, a manufacturer of commercial grade marine electronics.

6992WHALER posted 10-26-2011 09:03 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
That's interesting, In Canada this last summer a Canadian Coast Guard vessel showed on my AIS.
jimh posted 10-26-2011 11:04 AM ET (US)     Profile for jimh  Send Email to jimh     
In Canada, their Coast Guard is not operated as a military service. It is run more like a regular civil-service operation. In the United States, the USCG seems, now more than ever, to have become an adjunct of the military services, and their operation becomes more paramilitary, a distinct change from their previous and historical life saving, rescue, and safety mission.

Above note that encrypted AIS is done in accordance with NATO STANAG 4668. A little research on NATO STANAG 4668 shows it is a warship automatic identification system. Apparently when Homeland Security talks about the war on terrorism they are not kidding, and your local USCG small boat now operates like a warship in hostile combat in regard to encrypted AIS.

I have a very good friend who was a CWO4 in the Coast Guard Reserve and only recently retired or detached from reserve duty. He used to say that often they'd conduct patrols which he described as "showing the flag," which I interpreted to mean just having a presence on the water and letting people see the USCG vessel underway and on duty.

It seems a bit incongruous that the USCG would recommend its vessels use only encrypted AIS transmissions while they were conducting routine, overt, and normal patrol. What better way to "show the flag" than electronically via an AIS transmission?

6992WHALER posted 10-26-2011 11:39 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     
I see your point, but if I wanted to sink a ship, it sure would be nice to know exactly what course and speed it was traveling. It is an interesting Catch-22.
David Pendleton posted 10-26-2011 02:24 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
It would appear that this [that is, the use of encrypted AIS as the recommended mode of operation for USCG vessels] is designed to deny the public the ability to monitor a vessel via AIS, as any government would have the ability to monitor the above-mentioned frequencies and determine a ship's presence and position based on that alone.

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