CEOI
thanks Sapper1

• The CEOI is a document designed to control communications. Each edition contains the necessary material and information for 1 month. The following list shows the various items which may be found in a CEOI:
• Handling instructions.
• Index.
• Suffixes.
• Radio call signs and frequencies. Item number identifiers.
• Sound signals.
• Panel signals.
• Wire tagging system.
• Interference reports.
• Message reference numbers.
• Field telephone instructions.
• Telephone switchboard designators.
• Pyrotechnic and smoke signals.
• Signs and countersigns.
• Transmission security instructions.
• Key list.
• Operations code.
• Authentication instructions.
• Transmission authentication tables.
• Numeral cipher/authentication system.

This appendix will not explain the use of all of these items. Further information can be found in FM 24-1. PHYSICAL SECURITY AND COMPROMISE

The CEOI is classified if its contents require it. Normally, operational and contingency CEOIs are classified CONFIDENTIAL. Administrative or training CEOIs are usually classified to make their handling easier. Classified CEOIs must be handled with all the precautions associated with any classified document. The CEOI possibly can be compromised. As a precaution, the complete CEOI will not be taken forward of a battalion headquarters. Only a 10-day segment of the CEOI is issued to the user at any one time. If compromise occurs, it must be reported through the chain of command immediately. A CEOI is considered compromised when any portion of it is lost, captured, or exposed to unauthorized personnel. Another case is when the contents are so misused they endanger the security of the communications system.

CALL SIGNS

A call sign is a letter-number-letter combination assigned to a unit. Every unit in an organization has a different call sign.
The complete call sign is used under the following conditions:

• When opening a net.
• When entering a net in which you do not normally operate.
• When responding to a net call.
• When requested by NCS or any other station.
• When radio reception is poor.

At other times the last letter of the call sign with the suffix can be used. The last letter will be different for all stations in a net.

SUFFIXES

Call sign suffixes are two-number groups assigned to positions or activities within a unit. In a training CEOI, these are usually fixed. In an operational CEOI, they are randomly assigned on a daily basis. An expander letter can be attached to the basic suffix for further identification of positions or activities if required. The call sign and suffix together identify the sender and receiver of a radio message.

FREQUENCY ASSIGNMENTS

Each radio net is assigned a primary frequency and an alternate frequency. These frequencies change daily unless other instructions are given by the CEOI controlling authority. The daily change time is in the CEOI special instructions.

OPERATIONS CODE, AUTHENTICATION INSTRUCTIONS, AND TRANSMISSION AUTHENTICATION ASSIGNMENTS

These items explain the use of operations codes, the circumstances under which authentication is mandatory, and the use of transmission authentication tables. Columns in the transmission authentication table are also assigned to specific units. The numeral cipher/authentication system is explained as a separate item. Proper use of these items is critical to communications security.

Signal Operating Instructions (SOI)

The company commander or the RTO would carry the Signal Operating Instructions (SOI) which contained the frequencies and call signs of all units in the area and day codes. This enables you to send and receive coded messages. The SOI provides the organisation of stations into nets, assigns call signs, designates net control stations (NCS), and assigns frequencies. It also provides information on changes to alternate frequencies and on authentication. In addition, the security procedures that must be used by radio operators in the command are included in the SOI supplemental instructions. If you are an RTO then it would be advisable to create a pocket sized SOI for yourself. Decide which callsigns and frequencies you will use and the authentication send and reply codes. Make sure this book doesn't fall into enemy hands!

Tatical Callsigns

Call signs are used in radio communications to identify a communications facility, a command, an authority, or a unit. There are two forms of call signs: Complete Call Signs and Abbreviated Call Signs. Complete call signs usually consist of a letter - number - letter combination and a suffix, or a name and/or number. These are used when entering a net in which you do not normally operate. Abbreviated call signs are used at all other times. Platoon call signs were always two digit consecutive numbers such as 41, 42, 43, 44. Call signs also consisted of pronouncable words Red Fox, but they tended to get warped into weird and colourful names like Robin Hood and Boo Peep.

EXAMPLES:

Complete Call Sign: A2 7-6-5-0
Abbreviated Call Sign: 7-6-5-0
If no confusion exists as to which operators are on the radio net, no call signs need be used.

Radio ID
Each and every Battalion, Company, Platoon, and Squad had a radio ID. Radio ID's are based on the tables below.
ALPHA BRAVO CHARLIE DELTA
Company A Company B Company C Company D

HOTEL LIMA MIKE NOVEMBER OSCAR ECHO

Headquarters
Platoon First
Platoon Second
Platoon Third
Platoon Fourth
Platoon Recon
Platoon

Take the 2-7 Air Cavalry Re-enactment group. They are, 2nd Battalion, Alpha Company, 1st Platoon and operate 1st and 2nd Squads. vTheir Radio ID's are 2 (2nd Battalion) ALPHA (Company A) LIMA (1st Platoon) 1 (1st Sqaud).
Thus their Radio ID is shortened to:
2 ALPHA LIMA 1 or 2 ALPHA LIMA 2

Platoon & Squad Leaders Id
6 5 4 3 2 1
Commanding
Officer Next in
Command Weapons Sqaud
Leader Third Squad
Leader Second Squad
Leader First Squad
Leader
When Platoons and Squad Leaders send each other messages, sometimes they are identified as a number. Thus if you heard "THIS IS RED FOX 6, OVER" you would be hearing Red Fox's commanding officer. The Commanding Officer or Senior Officer of a Unit is always a "6". Next in command is always a "5". Weapons squad leader is a "4". Third squad leader is a "3". Second squad leader is a "2". First squad leader is a "1".

Authentication

Combat experience in Vietnam proved that false radio communications by the enemy contributed to substantial numbers of casualties and caused many missions to fall short of desired results. Proper authentication procedures can prevent an enemy from posing as a friendly station. The enemy is adept at radio communications and needs only a moderate degree of skill to seriously affect communication when we do not authenticate. A balance has to be struck so that effective communications is maintained without harassment of friendly communications. Authentication is one of the best means available to stop enemy infiltration efforts.
Operators are required to authenticate when they:

• Suspect a transmission is from an enemy station operating in the net (deception).
• Direct a station to go to radio silence or to break that silence.
• Are challenged to authenticate.
• Talk about enemy contact
• Give an early warning report, or issue any follow-up report.
• Transmit directions, which affect the tactical situation such as "Move to..." or "Turn off the radio."
• Cancel a message.
• Open the net or resume transmitting after a long period of silence.
• Transmit to someone who is under radio listening silence.
• Transmit a classified message in the clear.
• Transmit messages in the blind; that is, neither desiring nor expecting a reply.

Challenge if you are not sure that authentication is required. If a station takes more than 5 seconds to authenticate, rechallenge. Why 5 seconds? Because an enemy operator may try to contact another station and have it respond to that same challenge, thereby obtaining the appropriate reply to your challenge. This might be followed by a radio authenticator if you were entering a radio network for the first time. This involves a challenge and a password. This is to make sure the transmission is not an enemy imposter. A typical response could be:

RTO 1: This is BULLDOG 6. 2 ALPHA LIMA 1, OVER"
RTO 2: "ROGER BULLDOG 6, AUTHENTICATE HOTEL LIMA, OVER"
RTO 1: "I AUTHENTICATE ALPHA, OVER"
RTO 2: "ROGER BULLDOG 6 THAT IS CORRECT"
RTO 2 has worked out the code from a simple authentication table like the one below. The letters A to Z, printed in the sequence on the left hand side of the table are the Row Designators. The numbers 0 to 9 also represent those letters. So that if either the two test elements are a number then the adjacent letter is used. E.g. if 4 is is part of the challenge, then E is used.

Assume that the RTO is challenged with the two test elements HL. The correct method of authentication is to use the first letter to the right of the last test element. To do this: 1) First locate the first test element, "H" in the colomn of Row Designators.
2) Scan across the row designated by "H" to find the second test element "L".
3) The first letter to the right of "L" is A. Therfore the challenged RTO would respond "ALPHA".

If the second test element happens to be the last letter in the row, then use the first letter in the same row as the authenticator e.g. as if HO were used then the authenticator would be U. When challenging, try not use the same pair of test elements. Remember the enemy is alwasy listening.

Authentication Table

Note: Transmission authentication is used only when it is impossible or impractical to use challenge-reply authentication. For example:

HELLCAT THIS IS fOXHOUND 3 DO NOT ANSWER TURN EAST AT CROSSROAD X-RAY
AUTHENTICATION IS VICTOR PAPA
I SAY AGAIN
HELLCAT THIS IS FOXHOUND 3 DO NOT ANSWER
TURN EAST AT CROSSROAD X-RAY
AUTHENTICATION IS VICTOR PAPA
OUT


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