Signal Operating Instructions (SOI) For The Tactical Environment

Posted: 10/26/2013 in Communications

This article deals with another aspect of the communicate portion of the often used term “SHOOT, MOVE, and COMMUNICATE.” While most of us tend to use that term in reference to the three most important requirements while engaged in a fire fight, or as my Team Daddy used to call it “Hookin’ and Jabbin with the bad guys” (he was inclined to sudden, exceptional levels of violence on the personal level), the term has a much broader connotation.

The word “communicate” has relevance in all aspects of planning and execution of tactical operations. You must effectively communicate with all members of your organization while planning and during the execution of an operation. The communication aspect impacts all members of your organization; whether it is the folks manning the base station radio back at home, the Quick Reaction Force (QRF) you’ve established to deal with emergencies both inside and outside of your retreat, the folks manning perimeter positions around your retreat, LP/OP personnel providing early warning outside “the wire” or members of an active R & S (Recon and Surveillance) Patrol that should be constantly working your AO and AI. As an aside; If you don’t know the difference between an AO and AI go over to Guerrilla Sam has written a good article regarding both.

SOI is the acronym used by the U.S. Army for it’s code book of communication instructions. I call it a code book because, when developed and used properly, it provides those operating in a tactical environment the ability to communicate in a relatively secure manner. It has the added advantages of decreasing radio on-air time and minimizes most types of communication confusion and errors.
This is the example SOI we will be working with:

SOI 1 in effect 0500Z26OCT13 until 0500Z27OCT13

1. Organization call signs:
C/S                   Suffix
Company           R5T
Cdr                   6
1PL                   1
2PL                   2
3PL                   3
1SL                   11, 21 or 31
2SL                   21, 22 or 32
3SL                   31, 32 or 33
ATL                   A
BTL                   B

2. R&S to Base communications:
Primary:             Radio 1 primary 144.250MHz alternate 223.750MHz
Alternate:          Radio 2 primary 151.820 MHz alternate 154.600Mhz
Contingency:    Pin Flares IAW SOP
Emergency:      Visual Signal-17 Panel IAW SOP
Guard:               Radio 2 151.940MHz

3. Inter patrol communications:
Pri:                      Hand and arm signals per SOP
Alt:                      Radio 2 primary 151.880MHz alternate 154.600MHz
Con:                    Voice commands
Emr:                    Whistle per SOP

4. Telephone Circuit:
Location            C/S                  Wire Tag
Base                 Base
North Bunker    Bunker 1           Blue
West Bunker     Bunker 2          Red
North LP/OP     LP1                  Green
East LP/OP       LP2                 Yellow
Base shall make a net call with all occupied positions every half hour. Net call failure by any occupied position will initiate the QRF to that location.

5. Visual signals: as indicated

6. Recognition signals:
Pri:     VS-17 Panels – 1 Orange 1 Magenta
Alt:     Blue Smoke
Con:   2 red pin flares 30 seconds apart
Emg:  sign / countersign

Pri:    Red lens flashlight – 3 flashes.
Alt:    2 red pin flares
Con:  3 whistle blasts
Emg: letter number combination

QRF response to occupied positions:
Primary:          Field Phone
Alternate:       Radio on guard frequency
Contingency: 3 blasts on air horn
Emergency:   Runner

7. Challenge and password: Linebacker/Screwdriver
Running password: Indian
Number combination: 13

8. Authentication word:
1 2 3 4 5 6 7 8 9 0

The SOI consolidates all signal information that is pertinent to an operation into a single master document. The SOI can contain the items in the following list. If you don’t have a need for a portion, leave it out.
1. Handling instructions: who gets what portions, the time periods it is good for, destruction procedures, etc.
2. Index: if the document is lengthy.
3. Radio call signs and frequencies: to id users and keep everyone on the same sheet of music.
4. Field telephone instructions and wire tagging system: telephone protocol, wire tagging if you have multiple lines coming back to a switchboard.
5. Visual Signals: pyrotechnic, smoke and panels.
6. Sound signals: whistles, sirens, horns: car, truck, and air horns, shots, blasts etc.
7. Signs/countersigns: to challenge unrecognized personnel
8. Transmission security instructions.
9. Key list: encryption key information for communication devices.•
10. Operations code.•
11. Authentication instructions: to challenge unknown radio operators
12. Transmission authentication tables.

Security: Portions of the SOI are then extracted and issued to those personnel that have a need. Maybe that’s where the term “need to know” comes from. For instance, the folks operating the base radio don’t need to know the running password for the day. That would be of use only to your perimeter guards, LP/OP and patrol members outside the wire. The perimeter guards and LP/OP that are manning field phones don’t have a reason to know the inter-team radio freqs that the R & S team are on. This keeps the ability for SOI information to be compromised to a minimum.

The current SOI time period is normally good for 24 hours. If you suspect it has been compromised in any way, destroy all copies and issue a new document. Deployed elements (patrols) should always have a memorized, emergency (guard) freq and password, in the event the SOI has been compromised while they are deployed and no method is available to get an updated version to them. If you really want to get high speed-low drag, each patrol should also have a verbal duress code memorized to indicate that they have been snagged and are being forced to make radio comms or forced to re-enter friendly lines (your perimeter), with bad guys in tow.

We will now discuss the simplified, conventional company sized SOI shown above. I use the term simplified because you can really get lost in the weeds if you have to designate every swinging dick in the unit with their own call sign suffix. You can tailor it to fit your needs.

Effective Time Period of the SOI. The time period that this SOI will be used from start to finish, usually listed as a date time group. The date time group is listed in Zulu time to allow coordination with other units and services. Local time is fine for our needs. At the end of the time period all data in the SOI will change; c/s , c/s suffixes, freqs, authentication word……..everything changes.

Call signs. Normally used in a radio net to identify the unit and entities within the unit. The basic format is alpha/number/alpha, ie: R5T (Romeo Five Tango) and is randomly chosen. In the Army, the basic call sign represents the unit, which for our purposes is the company. Suffixes to the call sign such as R5T 31 designate positions within the company.

Suffixes. If you are talking to the radio operator for the company he will use the company call sign, which in this case is R5T. If you were talking to the Co Cdr the call sign would be R5T6. The Co Cdr’s suffix is always 6.

When talking to the 1st Platoon Leader (1PL) and other companies are on the net, his full call sign is R5T1. If you are talking on the company net it can be abbreviated to T1.

When talking to the First Squad Leader (1SL) from 1st Platoon his full call sign is R5T11 or 11 on the company net. Third Squad Leader (3SL) from 2nd platoon would be R5T23 or 23 on the company net.

At fire team level you would add the suffix ‘A” or “B” to the 2 digit squad c/s. 32A would be 3rd platoon, 2nd squad, team A.
Since most of us will not be operating in company sized elements within battalion sized elements, you will most likely scale down the scope of your SOI. If, for instance, you are operating out of a fixed base with two small R & S teams working your AI, you can designate the base as the main three character callsign with 2 suffix callsigns for the teams. I will cover the construction of an SOI utilizing a different, random number structure in a future post.

Frequencies. Next we list all radio frequencies or channels if pre-programmed. Be sure to list a primary and an alternate frequency for each type of radio used. Try to separate the freqs as far as possible in case of jamming or heavy use on the primary so that you can attempt comms on the alternate. Also note the use of the acronym PACE to denote the four levels of communication; Primary, Alternate, Contingency and Emergency.

Challenge and Password. For sentry use when unknown personnel are attempting to enter friendly lines.

Running password. Used when being pursued and required to re-enter lines on the run. The password is usually shouted when approaching the perimeter. Along the same line is the number combination password. In this case the number is 13. The challenge would be any number of lesser value such as 7 and the response is the number that when added to the challenge, in this case 6, would equal the password, 13.

The authentication word is a ten character word that contains no repeating letters. It is used to authenticate (validate) that someone on the other end of the communications is who they say they are. Use it only if you don’t recognize the voice on the other end. When challenged with a letter, you would respond with the following letter and the number directly below or some other combination previously agreed upon. Using our example, when asked “Call sign, this is call sign, authenticate Romeo, over”, you would respond with “call sign this is call sign, I authenticate Foxtrot Seven, Over”.

It should be apparent by now that learning to use the phonetic alphabet is pretty important. Take the time to memorize it, it can’t be that hard, every private in the Army is required to during basic training.

In future articles I will cover basic radio procedures and the creation and utilization of brevity codes that can be used to speed communications and make them more secure as well as integration of the SOI into the Base Defense Operations Center (BDOC) and the Tactical Operations Center (TOC).

  1. Jt rourke says:

    Thanks for the refresher. It’s funny how much one forgets when you don’t use it. TU

  2. Grenadier1 says:

    Good stuff sir good stuff!

    • III in CA says:

      I might be missing something…. “When challenged with a letter, you would respond with the following letter and the number directly below or some other combination previously agreed upon.”

      Where does the number directly below come from? Is that just a number sequence that the team has memorized?

      • danmorgan76 says:

        III, Refer to Item 8. Authentication Word in the SOI. The radio operator in my example received a call and did not recognise the voice on the other end. He would use one of the letters of his choosing in the word ” ANGLERFISH” to send the authentication challange to the unknown operator. In this case he challanged with the letter “R” (sent phonetically as “Romeo”). Before the team was deployed, in my example, the radio operators were informed to respond to any authentication challange with the next letter to the right of the challange letter (which is “F” or Foxtrot) and then the number directly below that letter (which is “7”) or F7, FOXTROT SEVEN.
        The base and team radio operators could have been told to reply with the letter three before the challange letter and the second number to the right of the number below the challange letter. You could make up any combination you wanted as long as it is agreed upon before the teams deploy. You should use it sparingly. If you use it ten times in a day, someone listening in would put your code together. Also, the word should change at least every 24 hours when you issue a new SOI. Something else I will mention in a later article, do not issue the same SOI to more than one deploying team. If you have two R&S or combat patrols outside the wire, each should have it own SOI and they should be nothing alike.

        Keep in mind when building an SOI, you must use words that have no reoccuring letters. They are easy to find online, then mark up an old paperback dictionary ahead of time.

      • John Doe says:

        brevity map, grid of squares with code word along left side vertically and same word horizontally like a map with letters and numbers would be replaced with a word that is and “x” amount of letters. Two letters in each vertical and horizonal grid would make a line to a grid square where there would be a phrase example: A & 0 would be “send help” ect.

  3. danmorgan76 says:

    III in CA, I just realized I didn’t properly answer your question. The authentication word is always 10 letters long. The numbers below the authentication word are always 1 through 10 with 10 listed as “0”. Each unique letter has it’s own unique number underneath it. Sorry for being so long winded. Hope this answers your question.

  4. Greygrandpa says:

    Many communications guys are radio hams. Learn and use some of the “Q” signals. Very few other than hams are even aware of them.

    • Joseph Plumb Martin says:

      This used to be case years ago in SF when the commo sgt used to have a ham ticket. SF has gotten so far away from HF that when I talk to newly graduated 18Es they know little to nothing of HF. Some years ago in Iraq I had the BN S3 demand that each team must send ONE sitrep one time by HF ALE using the 137 and a computer. It took a month. MSG Dan I know remembers doing this daily with HF and OTPs and getting the freq on a FIPS pad (if I remember correctly) and doing it with a leg key or a DMDG.
      I still send back replies on computer with QSL and I either get a yeah from an old time SF soldier or a question asking what does QSL mean from the new guys.

    • danmorgan76 says:


      QSL BT AR

  5. sparks31 says:

    Reblogged this on Signal Corps and commented:
    Good info. MSG Morgan’s blog is another one you should be following.

  6. the fukkn A-team says:

    Good stuff MSG Dan. I have to believe most Patriots skip right over the important comms skills and concentrate on the rambo gunslinging shit not realizing they are lost and out of touch without radio communications-arguably the more important of the 2. Keep the info flowing.

  7. Joseph Plumb Martin says:

    Time for me to brush up on my Morse code. Lots of free programs out there to help learn it and some computer programs to both send and read code.

    • danmorgan76 says:


      Here’s a link to the best Morse Code trainer I’ve found. I would recommend it for both folks learning IMC for the first time and old curmedgeons like myself (sounds like you might fall into that category also) who need to keep our speed up. I delete the characters they didn’t teach at Code School because, as you know, if the Army didn’t issue it to you, you don’t need it.


  8. ButchCass says:

    Right on, as an old Sky Cop, I never realized how much we did not know or use correctly. A great article.

  9. Good stuff! Looking forward to your articles mentioned at the end of this article.

  10. ncscout says:

    Reblogged this on brushbeater and commented:
    A great example of writing the Signals Operating Index by an expert in the field. Read and Heed folks.

  11. Jeff Daniel says:

    Can you send the links to the future articles you mentioned on brevity codes and radio procedures? I’m in the process of putting my comms book together.

  12. […] Writing an Operations Order, Report Formats and the Signals Operating Index […]

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