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Chapter 9

Shipboard Communications

Ship-to-ship and ship-to-shore communications are vital for shipboard operations. These communications can be by radio, radiotelephone, flag hoists, and blinker lights. The watercraft operator and mate aboard ship must be thoroughly familiar with their communication equipment. Shipboard communications are essential in normal operations, distress situations, and/or sea-air rescue missions. This chapter covers communications by radiotelephone, blinker, flag hoists, and the international distress signals.


9-1. All Army vessels are equipped with some kind of radio which is easy to operate. This paragraph covers the most common radio sets used aboard Army vessels. Even though the nature of radio communications has changed rapidly in the last few years, you will find it is as easy to talk on the radio as it is on the telephone.


9-2. Tactical radios are those used to communicate with your higher HQ and with other Army vessels. You will have either the AN/VRC-46 or the AN/VRC-47 aboard your vessel.
9-3. The AN/VRC-46 (Figure 9-1) is an FM radio set providing two-way radiotelephone communications (sea-to-sea, air to-sea, or land-to-sea service) within the frequency range of 30 to 79.95 MHz. It has a transmitter power output of 35 watts and it weighs 85 pounds. It has an output power requirement of 10 amperes maximum at 25.5 volts DC.


Figure 9-1. AN/VRC-46 Radio Set


9-4. The AN/VRC-47 (Figure 9-2) is an FM radio set providing two-way radiotelephone communications with Army land-based units, Army aircraft, and other Army vessels. It covers the frequency range of 30 to 79.95 MHz with a transmitter power output of 35 watts. It has an auxiliary receiver, which requires a separate antenna system, to monitor a frequency channel other than that normally used for operation. The total power input requirement is 10 amperes maximum at 25.5 volts DC. The set weighs about 105 pounds. The AN/VRC-47 is normally used only on command vessels or for certain special marine applications.


Figure 9-2. AN/VRC-47 Radio Set



9-5. Marine radio sets, often called "bridge-to-bridge" radiotelephones, are designed for vessel control and more informal communications. With them you can contact other vessels, even if they are not military, and receive civilian and Coast Guard emergency information. The requirement for carrying these radios is a US law and you cannot operate your vessel unless they work.
9-6. The DSC 500 (Figure 9-3) is a 25-watt (bridge-to-bridge) transceiver designed to communicate with other ships and shore-based radio stations. All international and United States VHF/FM marine channels in the frequency range of 156.025 to 163.775 MHz are accessible. The unit can also work 10 weather channels and 42 programmable channels. The DSC 500 has the following capabilities:
  • Directory entry of 200 ship to ship stations.
  • Directory entry of 50 coastal stations.
  • Can store up to 100 call waiting events.
  • Can store up to 50 group calls.
  • Can distress log up to 20 calls.


Figure 9-3. DSC 500 (Front Panel View)


The DSC is designed to cut down on excessive radio traffic and make radio calling more efficient. Typical Digital Selective Calling offers a better way of calling other vessels.


Channel 13 is to be used for bridge-to-bridge navigational purposes and it is monitored when underway. Channel 16 is the international calling and safety frequency (distress frequency).


9-7. If you connect your DSC to a navigation receiver (such as loran or GPS) your position can be given quickly to another vessel. Another vessel can request your position, in an emergency situation, through your radio.
Note: In order to provide the best fidelity at high volume settings, your DSC 500 uses a speaker with a strong magnet. If any rearranging of equipment in your wheelhouse becomes necessary, be sure to place the DSC 500 well away from your compass. Observe your compass during remounting to ensure that the radio is not effecting your compass heading. Remember that you will have to swing ship after any equipment in your wheelhouse is moved to determine the effects on your compass.
9-8. The AN/URC-92 (Figure 9-4) is a medium power, single sideband, high frequency, automatic tuned radio set able to transmit and receive upperside band, continuous wave, and amplitude modulation in the frequency range of 2.0 to 30.0 MHz. The set is capable of 100 watts of power output when transmitting SSB and compatible AM signals. The input power requirement is 115 volts AC, single phase, 60 Hz. This radio is for medium and long range communication with military and civilian stations with a range of 4,000 miles.


Figure 9-4. AN/URC-92



9-9. The GMDSS was developed by the maritime nations in the IMO. GMDSS was implemented on 1 February 1992 and has become mandatory for all new ships built after 1 February 1995. GMDSS should be installed on all ships by 1 February 1999 (unless this deadline is extended by the IMO). GMDSS is designed to ensure maximum coverage of safety communications for all passenger vessels and cargo vessels of 300 GT or more engaged in international voyages. The major reason for the GMDSS is to guarantee that complying vessels will be able to communicate at anytime (in case of distress or to exchange safety information) with a shore station or a ship. The GMDSS describes four sea areas based on the location and capability of shore-base communications facilities. These are described as follows:

Sea Area A1

9-10. An area within the coverage of at least one VHF coast station in which continuous DSC alerting is available (normally 20 to 30 NM).

Sea Area A2

9-11. An area, excluding Sea Area A1, within the coverage of at least one MF coast station in which continuous DSC alerting is available (normally within 150 NM).

Sea Area A3

9-12. An area, excluding Sea Areas A1 and A2, within the coverage of an Immarsat Satellite in which continuous alerting is available (normally everywhere on the globe except the polar regions).

Sea Area A4

9-13. An area outside Sea Areas A1, A2, and A3 which is in the polar regions.
9-14. GMDSS vessels carry the communications equipment appropriate to the Sea Area in which they are operating. GMDSS vessels also carry standard equipment that operates on the same frequencies and mode to ensure communication between other vessels.


9-15. It is important that you use the correct radio procedures when using the radio. Radio messages should be short and to the point. Speak slowly and distinctly and do not try to impress the other station with your knowledge of current slang terms or CB talk. Refer to FM 24-18 for complete radiotelephone transmitting instructions.
9-16. When talking on the bridge-to-bridge set (DSC 500), use plain language that can be understood. There are no requirements for special codes or words when using channel 13. Make sure the other person (whether civilian or military) can understand you. Speak clearly and use short sentences. The following practices are forbidden:
  • Violation of radio silence.
  • Unofficial conversation between operators.
  • Transmitting on a directed net without permission (except flash and immediate traffic).
  • Excessive tuning and testing.
  • Transmitting the operator's personal sign or name.
  • Unauthorized use of plain language.
  • Use of other than authorized prowords.
  • Unauthorized use of plain language in place of applicable prowords or operating signals.
  • Linkage or compromise of classified call signs and address groups by plain language disclosures or association with unclassified call signs.
  • Profane, indecent, or obscene language.
9-17. BE ALERT while transmitting by radiotelephone. Release your PUSH TO TALK BUTTON occasionally (usually after each phrase or two) to allow another station to break in, if necessary, and to listen for a few seconds for possible distresses.
9-18. Keep the receiver gain (volume control) turned high enough to hear weak signals through static and other interference.


9-19. The following are some important things to remember when calling or replying.
  • Listen on the frequency before transmitting to make sure that you will not interfere with another transmitting station.
  • Set your transmitter on the proper frequency.
  • Speak clearly, in a normal voice, holding microphone about 1 to 3 inches from your lips.
  • Reduce operating room noise level.
  • Avoid excessive calling and unofficial transmissions. Transmit call signs only once when communication conditions are favorable and twice when unfavorable.

When a station called does not reply to a call sent three times at intervals of 2 minutes, the calling with cease and will not be renewed until after an interval of 15 minutes. However, if there is no reason to believe that harmful interference wil be caused to other communications in progress, the call sent three times at intervals of 2 minutes may be repeated after an interval of less than 15 minutes but not less than 3 minutes. The DSC 500 will do the calling for you automatically and let you know when called station answers. This will free up the operator for other bridge chores.
  • End every transmission with either "OVER" or "OUT" (except when the sending operator wishes to pause a moment before continuing transmission). Use the proword "WAIT" in this instance. If you intend to pause for a longer period of time before resuming your transmission, use the proword "WAIT OUT". Never use OVER AND OUT together.


9-20. The following are the most important frequencies that are available.
  • 2182 kHz. This is for international distress and calling voice frequency. It may be used for distress, urgent, and safety traffic. (Safety messages should be sent on 2670 kHz after a preliminary announcement on 2182 kHz.) Ship stations and shore stations will also establish initial contact on 2182 kHz and then shift to an appropriate working frequency for the passing of operational messages.
  • 2670 kHz. This is a Coast Guard frequency. Use by non-Coast Guard stations will be restricted to communications with the Coast Guard. This is a normal working frequency for communications with nongovernment vessels after initial contact on 2182 kHz. Group stations also use this frequency for Coast Guard safety information broadcasts.
  • 2638 and 2738 kHz. International ship-to-ship frequencies. Coast Guard ships may use these frequencies to communicate with non-Coast Guard ships. They are authorized for use by certain shore stations only for communicating with non-Coast Guard vessels that are in distress situations when no other common frequency is available.
  • 3023.5 and 5680 kHz. International SAR on-scene frequencies. Either of these frequencies may be used to conduct communications at the scene of an emergency or as the SAR control frequency.
  • 156.3 MHz, Channel 6. International VHF-FM ship-to-ship frequency (nationally used by maritime mobile stations for SAR communications at the scene of the SAR incident).
  • 156.6 MHz, Channel 12. Port operation's working frequency. Coast Guard use of this frequency shall be limited to shore station communications with non-Coast Guard ships involving port operations.
  • 156.65 MHz, Channel 13. Vessel bridge-to-bridge VHF-FM frequency for navigational purposes.
  • 156. 7 MHz, Channel 14. Second choice port operation's working frequency. Coast Guard use of this frequency will be limited to shore station communications with non-Coast Guard ships involving port operations.
  • l56.8 MHz, Channel 16. International VHF-FM calling and safety frequency (nationally used also as a distress frequency). It may be used for calling or answering messages preceded by the distress, urgency, and safety signals.
Note: There are no restrictions on obtaining radio checks from Coast Guard Stations on 156.8 MHz.
  • 157.1 MHz. Primary liaison frequency for communications between nongovernment vessels and Coast Guard vessels and coast stations. Also used by the Coast Guard for the national VHF-FM radiotelephone safety and distress system and the Coast Guard Marine Information Broadcast Frequency.
  • 157.05 MHz, Channel 21; 157.15 MHz Channel 23. Intra-Coast Guard VHF-FM working frequencies. These frequencies are authorized for communications between Coast Guard units engaged in maritime mobile operations and are common to all districts.
  • 157.075 MHz, Channel 81. Joint command, control, and surveillance frequency. Used by US and Canadian mobile units, that are operating according to Marine Pollution Contingency Plan for Spills of Oil and Other Noxious Substances. This frequency is also authorized for other Coast Guard maritime mobile command and control operations when not required for marine environmental purposes.
  • 157.175 MHz, Channel 83. Coast Guard command and control frequency when required. Coast Guard auxiliary operational and training frequency in the VHF band. This frequency can also be used by Coast Guard Reserve training units (on a not to interfere basis) to Coast Guard operations.


9-21. You should be familiar with the standard international phonetic alphabet as shown in Table 9-1. It should be practiced and used for all transmissions. It is not a code; it is a means to better understanding of your radio transmission.


Table 9-1. Standard International Phonetic Alphabet





























9-22. This paragraph describes the CEOI and tells how to use it. The standing instruction, which explains how to use the CEOI, was published as a separate document called Communications-Electronics Standing Instruction. This instruction is provided to Army units in a two-part document. The first part (basic document) contains such items as the daily changing call signs, frequencies, suffixes, signs and countersigns, and pyrotechnic and smoke signals. The second part (supplement) contains handling instructions, general instructions, telephone switchboard designators, and other items that seldom change. A command simply combines these two documents in the field to make a complete CEOI. The CEOI now lists call signs using LNL combinations selected randomly by a computer.
9-23. Numbers are pronounced as shown in Table 9-2.


Table 9-2. Pronunciation of Numbers


























9-24. All CEOIs are a standard size: 4 1/4 x 4 3/4 inches. This size fits into a soldier's field jacket pocket for easy handling. They reach the major commands in a complete package assembled in a "layered" configuration; that is, parts of the package that apply to subordinate units can be readily separated and distributed. The exact makeup of each CEOI package is determined by the using command. Each major command C-E officer is responsible for developing the initial information. He must promptly report all changes or required updates to the preparing agency so the computer can keep pace as the officer's organization, plans, and programs change.

9-25. Each CEOI is issued in editions containing 10 time periods. This helps reduce the impact of possible loss or compromise. Should loss or compromise occur, the command merely shifts to the next edition.
9-26. The "heart" of the CEOI is the capability to change call signs, suffixes, and frequencies at least every 24 hours. It does not remove from the tactical commander overall responsibility for content and management of his command's CEOI system.


9-27. The commander of the unit for which the CEOI is prepared is the controlling authority of that CEOI. The C-E officer, acting for the commander, makes sure that the current CEOI is available to those who operate communications systems and that higher and adjacent organizations get copies.
9-28. All users must be familiar with the general and special instructions in the CEOI if effective and responsive communications are to be available. As mentioned earlier, your CEOI contains specific instructions for the operation of C-E equipment, systems, and facilities within your command. The command CEOI is the only authorized document from which subordinate elements will extract call signs and frequencies.


9-29. The CEOI contains general and special operating instructions. With these instruments in the CEOI, each communications user has in one package all the guidance he needs to operate tactical communications effectively. All CEOIs are designed to meet the needs of the organization they support while retaining a standard format.
9-30. On the index pages of the CEOI, you will find the contents are listed and identified by item number. These numbers are consistent throughout the Army. These item numbers are very useful when you are communicating with someone else who holds the same CEOI you do.


9-31. Field radio stations are grouped into nets according to the tactical situation. To control a net, one station, usually the one serving the highest echelon, is designated as the NCS. The authority of the NCS is absolute. The NCS opens and closes the net, grants or denies permission to enter the net, corrects errors in operating procedures, and maintains net discipline. The call sign assigned to the station controlling the net is the net call sign. For example, D5G28 is NCS of a division command net; D5G (with no suffix) is the net call sign.
9-32. Radio nets will normally be operated as free nets. In free nets, stations may exchange traffic without prior permission from the NCS. When traffic is heavy or when operators are inexperienced, the NCS may order a directed net. In this case, no station will transmit without first calling the NCS and requesting permission.


9-33. A call sign has two parts. The first part uses a random LNL combination, which is the basic call sign. The second part consists of two numbers (01 through 99) which make up the suffix. You can expand the suffix by adding a letter to identify a subelement (such as deputy or alternate). The last letter of the basic call sign is unique to the echelon at which the user operates. For example, in a battalion, no two stations would have the same last letter. The reason for this is that it permits an abbreviated call sign for routine use in a functioning net.
9-34. A complete call sign must be used any time a station enters or operates in a net in which it does not normally operate. A call sign must be used only during its effective time period. At no time will a new call sign be used on an old frequency. Likewise, an old call sign will not be used on a new frequency.
9-35. Call signs, suffixes, and frequencies are simultaneously changed daily throughout the organization or as directed by the commander. If you are suppose to change at an odd time, you will be informed through proper channels.
9-36. A frequency is assigned to a radio net for a stated period of time. The frequencies allocated to the command are assigned to designated nets by computer. This allows for nets to change frequencies at least once daily. It does not provide more frequencies but does allow better use of the frequency.


9-37. The automated CEOI is produced by the Director, National Security Agency, based upon requirements of the commander. It is shipped directly to the COMSEC custodian of each command. Distribution of the CEOI is limited to those units and individuals that must have them. The C-E officer makes these decisions. Subordinate C-E officers determine the distribution of CEOI items within their units and distribute the CEOI extracts required by their commands or units. C-E officers should refer to AR 25-1 for detailed information concerning requisitioning of CEOIs.


9-38. Holders of the CEOI will be issued two training editions and a minimum of 90 days of operational/reserve editions. The controlling authority keeps reserve editions of CEOI items to ensure rapid replacement. When reserve editions are issued, replacement editions must be obtained from NSA according to AR 25-1.


9-39. The CEOI is classified, if required, by its contents. Normally, operational and contingency CEOIs are classified CONFIDENTIAL. Administrative or training CEOIs are UNCLASSIFIED to make their handling easier. Those CEOIs classified CONFIDENTIAL or above must be given the physical security safeguards and requirements set forth in DOD 5200.1-R and AR 380-5.
9-40. The CEOI belongs to the organization for which it was produced. The commander is responsible for efficient and secure handling procedures. The commander is the recognized controlling authority and has the authority to use the unclassified call sign and frequency change programs for training purposes.
9-41. Additional physical constraints are necessary to lessen the possibility of unauthorized disclosure. The complete CEOI will not be taken forward of a battalion CP. No more than 10 days material is issued to the user at any time.
9-42. The individual in possession of a CEOI, or a portion thereof, is responsible for safeguarding its contents. A thorough understanding of handling procedures established by the unit, combined with good common judgment, will greatly assist in keeping the CEOI away from unauthorized personnel.
9-43. The CEOI, or any portion of it, is considered compromised when it is lost, captured, exposed to unauthorized personnel, or when the contents are so misused they endanger the security of communications systems.


9-44. Any individual having knowledge of a compromise, suspected compromise, or loss of a CEOI must advise the controlling authority immediately by the most expeditious secure means available. It is very important that this information be reported to the controlling authority so that the situation can be evaluated and contingency precautions implemented. A written report must be submitted within 48 hours after the initial report. The report should include complete details and circumstances of the compromise, suspected compromise, or loss.


9-45. Two CEOIs are normally provided to a command in two versions. One is a training CEOI and the other is an operational reserve CEOI. Training versions are used when the command is not engaged against a hostile force. Two training editions are held by each command. These editions are unclassified and marked FOR OFFICIAL USE ONLY. They are recycled within the command until the copies are worn out. Replacement editions for training purposes may be requisitioned according to AR 25-1 when the material is worn out or when major organizational changes occur.
9-46. Operational/reserve CEOIs are held in reserve and will be implemented only when a unit becomes involved in operations against a hostile force or when instructed by the controlling authority. Operational/reserve CEOI material is classified at least CONFIDENTIAL. The NSA resupplies CEOI material, according to AR 25-1, as the operational editions are used. In situations where operational material is used routinely, resupply will be automatic. Otherwise, operational editions are resupplied only when the controlling authority requisitions them.


9-47. The Director, National Security Agency produces the CEOI. It is shipped to the COMSEC custodian of each command. Distribution is handled through armed forces courier service channels. Radio call signs, suffixes, and frequencies are assigned by automated techniques using data submitted by the using command. This procedure ensures that unique LNL call signs are provided for each tactical unit for which the CEOI is designed. To do this, the C-E officers of major commands furnish NSA specific input data according to AR 25-1. The input data required consists of the following:
  • Organizations to be assigned call signs.
  • Nets to be assigned frequencies. Nets requiring fixed frequencies and the list of frequencies must be furnished.
  • All nets that share, or may possibly share, a common site, such as a command post or tactical operations center.
  • All frequencies (in MHz) available to the command for assignment. Power restrictions imposed on the frequencies must also be indicated.


9-48. A CEOI may be manually prepared by a command when circumstances are such that an automated version is not available or must be updated. The manually prepared CEOI must follow the format of the automated CEOI and embody the principles of changing call signs, suffixes, and frequencies at least every 24 hours. This is done by first contacting the command's supporting US Army Intelligence and Security Command unit and asking for help. They have prepared, in conjunction with NSA, a call sign and suffix list plus standard nonchanging supplemental material for use by Army commands. The responsibility for manual CEOI preparation rests solely on the tactical command, which produces the manual system.
9-49. A sample of the computer-generated list of call signs, structured in time periods without unit designations, is shown in Figure 9-5.


Figure 9-5. Sample Computer-generated List of Call Signs


9-50. Use visual signals when your radio goes out or radio silence is ordered. Also use them when you need to get a message to that ship you are unloading or to the next boat in your convoy. Sending someone over in a boat is a possibility, but not usually a good idea. There are different types of visual signals. This paragraph will give you the basic information you will need to know about the international signal flags and flag hoist methods. Paragraphs 9-58 through 9-64 discusses flashing light signals and their application with Morse code. Although pyrotechnics (signal flares) are used less often, they are covered in another chapter.


9-51. Signaling by flag hoist is a method of communication in which a set of flags of different patterns and colors is used. The set consists of 26 alphabetic flags, 10 numeral pennants, 3 substitutes, and 1 answering pennant.
9-52. There are six single letter flag hoists that all crew members should immediately recognize (Figure 9-6). These signals warn the mariner of danger or are an urgent request for assistance. Any vessel seeing one of these signals will immediately take the proper action. Even though these six flags warn of danger, mariners should know all 26 signal flag hoist meanings from memory.
9-53. Except for proper names, the international signal alphabetical flags are used only to send messages by code. Each flag has a meaning by itself in addition to the alphabetical meaning. Each flag will also have a different meaning when used with another flag. For example, the "A" flag by itself means "I have a diver down; keep well clear at slow speed." If you hoist two flags that read "AC," it means "I am abandoning my vessel." Two and three letter signals are described in Pub. No. 102, International Code of Signals.

Figure 9-6. Urgent Code Flags

9-54. It is possible to communicate with several ships at one time if the flags are visible to all. Simple signals for towing and other activities may be worked out between vessel masters to make routine movements easier.
9-55. This method of signaling is slow and not suitable for the transmission of long messages. Flag hoists may be used only for short distances and cannot be seen in heavy weather or darkness.


9-56. Do the following to use the flag hoist system:
  • As transmitting vessel, hoist signals where they can best be seen by the receiving ship and make sure they blow out clear and are free from smoke.
  • Fly each hoist or hoists until answered.
Note: A signal is superior to another when hoisted first or in time or position.
  • When more than one signal is shown on the same halyard, separate each one from the other by tacklines. Always read from the top down.
  • When several hoists are displayed at the same time, read in this order: masthead, triatic stay, starboard yardarm, and port yardarm.
  • When more than one hoist is shown on the same yardarm, read from outboard to inboard (Figure 9-7).

Figure 9-7. Order of Reading Flag Hoists on Yardarm


9-57. Do the following to answer flag hoist signals:
  • Hoist the answering pennant at the dip as soon as you see each hoist. As soon as you understand the signal, immediately close up the pennant.
  • Lower the answering pennant to the dip as soon as the hoist is hauled down; close up again when the next signal is understood.
  • Keep the answering pennant at the dip if you do not clearly see the message. If you can see but cannot understand the message, hoist "ZQ -- Your signal appears incorrectly coded. You should check and repeat the whole," or hoist "ZL -- Your signal has been received but not understood."


9-58. Sending messages by flashing lights, using the Morse code, is one form of visual communication from ship-to-ship and from ship-to-shore. The flashing or blinker light has several advantages. It may be used when a radio is not available or when security prevents the use of radio. Brief messages may be sent with considerable speed. A portable flashing light is useful on small craft where size and construction prevent the installation of elaborate equipment.
9-59. There are certain disadvantages in the transmittal of messages by blinker light. This method is not very good for sending long messages because it is comparatively slow. Range is limited even under ideal conditions. Atmospheric and light factors may prevent its use.


9-60. Morse code (Figure 9-8) is a system of signaling using a series of long and short light flashes or sounds. It is still the only way flashing lights can be used, and in that form is used on almost all Army vessels. All deck personnel should memorize Morse code.


9-61. Blinker lights vary in size, shape, and power source, yet they all work the same way. One type of blinker, the Aldis Gun (Figure 9-9) consists of a tube closed at one end with a light inside. The light is turned on and off by a trigger-operated switch. The portable type blinker can get its electric power from either batteries or the ship's electrical system. The blinker lamp is fitted with a control knob that is used to dim or brighten the light.

Figure 9-8. International Morse Code

Figure 9-9. Aldis Gun


9-62. Prosigns are a form of visual communication shorthand. They give in brief form certain orders, requests, instructions, and other information that often comes up in visual communications. Figure 9-10 shows some of the more common ones that may be used. Those prosigns that are overscored are sent as one signal without a break between the letters.

Figure 9-10. Procedure Signs


9-63. The flashing light system uses the international Morse code. This is the dot-and-dash system. Most people do not use the term "dots and dashes." Instead they will say "dits and dahs;" the "dah" rhyming with "baa." It is much easier to learn the code by calling out the short flashes of light as "dits" and the longer light flashes as "dahs." When you hear the code called out in this manner, it makes for an easy rhythm. Figure 9-11 shows the desired spacing between dots and dashes for the simple message "we are here."
Note: The dots are one unit long and the dashes are about three units long. The space between the dots and dashes of a letter is one unit; between letters, three units; between words, seven units.

Figure 9-11. Spacing Used for Simple Message


9-64. The following are a few hints you can use when signaling:
  • Never send blinker faster than you can receive.
  • Have your message written out before you start to send.
  • During daylight hours, aim the signal lamp directly at the receiving ship.
  • At nighttime, aim the signal lamp at the water, just below the receiving ship's waterline. During times of darkness, you will NEVER aim the signal light onto the other ship's bridge.
  • Look to one side when receiving blinker at night. DO NOT look directly at the light.
  • Note: There are filters available that can be attached to the flashing light during hours of darkness. Then the light can be directed at the receiving station.
  • Write each letter as soon as it is received. If you miss a letter, go to next letter. When the word is completed, you can go back and fill in the space. If you try to figure a letter in the middle of a word, you are apt to miss the next letter or letters being sent.


9-65. Sailing can be hazardous. Even with today's modern electronic aids to navigation and worldwide radio and satellite communications systems, ships still sink. If you get into trouble, your greatest aid will be the distress signals you send out over the radio. International agreements and US laws have set up special frequencies that will be used for nothing but distress signals. There are also special message formats and key words to use if you are in trouble.


9-66. Depending upon the type of radio you have, there are different frequencies to use for distress signals. Army FM tactical radios cannot be tuned to any of the frequencies. These frequencies are to be used FOR EMERGENCY CALLS ONLY. Once you have established contact, you will be told to change to another frequency to arrange any necessary rescue.
9-67. The most widely used emergency frequencies are 2182 kHz and 156.8 MHz on the marine radio (channel 16 on your URC-80). For vessels equipped with the longer range CW sets, 500 kilocycles has been established as the emergency frequency. Most vessels and shore stations with the capability will keep watch on the 500 KC frequency, so they can relay or respond immediately if an emergency arises.
9-68. The 500 KC frequency can also be used for safety and urgent advisory messages. An international silent period on this frequency has been established to enable any vessel in distress to have a clear channel for requesting help. The silent period is observed twice every hour, from 15 to 18 minutes after the hour and from 45 to 48 minutes after the hour. Do not make any calls during these periods unless distress, urgent, or safety matters are involved. If you are transmitting a routine call on 500 KC and notice that you are running into the silent period, transmit "AS" which means "Wait." When the silent period has ended, you may again resume transmission. In addition to being very careful not to transmit on 500 KC during the silent period, you should listen carefully on that frequency for distress messages. If you hear any station making illegal transmissions during the silent period, the nature of the transmission and the call sign of that station should be noted in your radio log.


9-69. The distress signal MAYDAY indicates that a ship or aircraft is threaten by grave or imminent danger and requests immediate assistance. The distress call has absolute priority over all other transmissions--and need not be addressed to any particular station. If you hear a distress call, immediately cease transmissions that might interfere with the distress traffic and continue to listen on the frequency over which the call was heard.
9-70. Distress transmissions are normally made on the distress frequencies 156.8 MHz (channel 16) or 2182 kHz. They may be handled over other frequencies if the need arises. A distress call consists of the following:
  • Distress signal MAYDAY, spoken three times.
  • The words THIS IS.
  • Call sign of the distressed unit, spoken three times.


    -- THIS IS -- LCM 2348, LCM
    2348, LCM 2348."
9-71. Normally the distress message will immediately follow the call. Be prepared to copy all information heard. A distress message consists of the following:
  • Distress signal MAYDAY.
  • Distress unit's call sign. Particulars of position, nature of distress, type of assistance desired, unit's description, persons on board, and any information that might aid the rescue.

Distress Message Repetition

9-72. The distress message, preceded by the distress call, should be repeated until you receive an answer. The repetitions should be preceded by the alarm signal whenever possible. If you receive no answer to a distress call on a distress frequency, the message may be retransmitted on any frequency available on which attention might be attracted.

Attracting Attention to a Distress Call

9-73. If you receive a distress call and are unable to make contact with the distressed unit, take all possible action to attract the attention of stations in a position to give assistance. Also pass along as much information concerning the call as possible.

Receipt of Distress Messages

9-74. When a distressed unit is in your vicinity, answer the message immediately. However, if the unit is some distance from you, pause a few moments to allow ships or stations nearer the scene to answer.
9-75. In areas where communications with one or more shore stations are practicable, ships should wait a short period of time to allow them to answer.
9-76. Receive distress messages in the following manner:
  • The call sign of the unit in distress, spoken three times.
  • The proword THIS IS.
  • The call sign of the unit acknowledging receipt, spoken three times. The words RECEIVED MAYDAY.
  • Request essential information needed to effect assistance. Obtain less important information in later transmission. Inform unit to stand by.
  • The proword OVER.
9-77. If you receive distress traffic, you should do the following by the most rapid means:
  • Forward distress information to the harbormaster or higher HQ.
  • Set a continuous radio watch on frequencies of the distress unit.
  • Maintain communications with the distressed signal.
  • Maintain distress radio log.
  • Keep higher HQ informed of new developments in the case.
  • Place additional men (if available) on watch (if necessary).
  • Obtain radio direction finder bearing of distressed unit if equipment and conditions permit.


9-78. A vessel or seaplane that is in distress can use the following distress signals to tell other vessels or people ashore that help is needed. The vessel in distress may use more than one distress signal.
9-79. The distress signals are from the international regulations for preventing collisions at sea. The following signals are recognized by all maritime nations:
  • Firing rockets or shells, which throw red stars once every minute.
  • Constant sounding of any fog signal apparatus.
  • Creating flames on the vessel (burning a tar barrel, oil barrel, and so on).
  • Firing a gun or other explosive, once every minute.
  • A piece of orange-colored canvas with either a black square and circle or other appropriate symbol for identification from the air.
  • Firing a rocket parachute flare with a red light.
  • A dye marker of any color.
  • Hoisting the international signal flags which indicate "November Charlie." November: White and blue checkered flag. Charlie: horizontal striped (blue, white, red, white, blue) flag.
  • Hoisting a square flag with a ball, or something that looks like a ball, above or below it.
  • Standing on deck with arms outstretched to each side slowly and repeatedly raising and lowering arms.
  • Igniting an orange smoke signal.


9-80. There are several types of messages which are peculiar to marine communications and which you must be thoroughly familiar. By international agreement, the order of precedence for these messages are as follows:
  • Distress call (including the autoalarm distress signal), distress messages, and distress traffic (SOS or MAYDAY).
  • Urgent signals and messages (PAN).
  • Safety signals and messages.
  • Communications relative to radio direction-finding bearings.
  • Communications about the navigation and safe movement of aircraft.
  • Communications about the navigation, movements, and needs of ships, including weather observation messages for an official weather service.
  • Government communications for which priority rights have been claimed.
  • Service communications relating to the working of the radio-communication service or to communications previously transmitted.
  • All other communications.
9-81. You should know this precedence, but you should remember that your primary responsibility is the proper handling of military traffic. If it does not interfere with the proper completion of your military mission, you may assist commercial stations (but only with the permission of the vessel master).
9-82. Except in cases of emergencies, operators aboard Army vessels are not authorized to transmit commercial or personal messages. Only official messages may be handled and they should be transmitted only through Government facilities. Under certain conditions, it may be necessary for you to send a message through a commercial station, especially if distress, urgent, or safety matters are involved. Commercial stations make no charge for handling such messages.


9-83. The urgency signal PAN (pronounced PAHN) indicates that the station calling has an urgent message concerning the safety of a vessel, aircraft, or person on board or within sight. Send the signal and message on a distress frequency (156.8 MHz [channel 16] or 2182 kHz) or any other frequency that may be needed to get the required help.
9-84. The urgency signal has priority over all other communications except distress traffic. The message preceded by the urgency signal is usually addressed to a specific station. However, it may be addressed to ALL STATIONS.
9-85. If you hear the signal, listen on that frequency for at least 3 minutes. If nothing is heard following the urgency signal, you may resume normal communications. Do not interfere with urgent traffic. Normal work may continue on frequencies other than that on which the urgency signal was heard provided the message was not addressed to ALL STATIONS.
9-86. The urgent message should contain all details concerning the particular case and be in plain language form. If you receive an urgent message, deliver it by the most rapid means to your next higher HQ or harbormaster.


9-87. When the urgency signal has been sent before transmitting a message to ALL STATIONS, which calls for action by the stations receiving the message, the station responsible for its transmission will cancel it when action is no longer necessary. This message of cancellation shall likewise be addressed to ALL STATIONS.


9-88. The safety signal consists of the word SECURITE (pronounced SAY-CURE-E-TAY). It means that the station is about to send a message concerning the safety of navigation or it is giving important weather warnings. When you hear this message, inform your vessel master at once. The safety signal and call will be sent on the distress frequency or one of the frequencies that may be used in case of distress.


9-89. The safety message will normally be sent on a working frequency, but an announcement to this effect will be made at the end of the silent period on the distress frequency.

Example: (Preliminary call on distress frequency).

9-90. When you hear the safety signal, listen to the safety message until you are satisfied that the message is of no concern to you. Do not make any transmission that will likely interfere with the message.


9-91. Radio stations specializing in weather broadcasts are operated by the United States Weather Bureau. These stations have a limited range so the weather forecasts they send out are usually local weather. Your URC-80 has a special "W" channel for these weather broadcasts. As you move along the coast, you will find that the stations fade and are replaced with different ones. When overseas, you will have to rely upon local arrangements for weather forecasts, usually obtainable through your company operations section from the Battalion S2.


9-92. The following publications are needed for shipboard communications.

International Code of Signals (Pub. 102)

9-93. This publication lists all the internationally recognized signals, codes, distress signals, and rules to be employed by vessels at sea to communicate a variety of information relating to safety, distress, medical, and operational information. Each signal has a unique and complete meaning. This publication also contains the internationally recognized message formats and complete instructions for all the forms of communication. Pub. 102 is published in several different languages to make it easier to communicate with the crew of foreign vessels.

Radio Navigational Aids (Pub. 117)

9-94. This publication is a selected list of worldwide radio stations which perform services to the mariner. Though this publication is essentially a list of radio stations providing vital maritime communication and navigation services, it also contains information which explains the capabilities and limitations of the various systems.


9-95. If you are in distress, that is, if grave and imminent danger threaten you, transmit your emergency on the international distress frequencies: 2182 kHz and 156.8 MHz (channel 16).

9-96. If you are merely having difficulty (for example, engine trouble, steering failure, and so forth) and need help, the Coast Guard can be reached by calling on either of the two distress frequencies. The distress call sent by voice radio consists of the following:
  • The distress signal MAYDAY spoken three times.
  • The words "THIS IS" or the letters "DE," (spoken as DELTA ECHO in case of language difficulties) and your vessel's call signal and name.
9-97. If you are not in immediate danger, you will be shifted to a common working frequency for further communications. This keeps the distress channel open for other emergencies.

9-98. After you have made contact, speak slowly and clearly to avoid confusion and delays. Give the following additional information:
  • Your vessel's position in latitude/longitude or true bearing and distance in nautical miles from a widely known geographical point. Avoid using local names that are known only in the immediate vicinity, as they can be confusing (for example, "buoy l9," or "the rocks").
  • The nature of the distress or difficulty.
  • The kind of help needed (for example, medical, air evacuation, damage control, and so forth).
  • The number of persons aboard and the condition of any injured.
  • The present seaworthiness of your vessel.
  • A full description of your vessel including length, type, cabin, masts, power, color of hull, superstructure and trim.
9-99. The voice radio alarm signal, if available, should be transmitted for about 1 minute before the distress call. The voice radio alarm signal consists of two audiotones of different pitches transmitted alternately. 9-100. The radiotelegraph alarm signal is 12 dashes. Each dash is 4 seconds in duration with 1 second of silence between dashes. As in voice radio, the alarm signal comes before the SOS. 9-101. The purpose of these two alarms is to attract the attention of persons on watch and should be used to announce that a distress call or message is about to follow. Some Army and most commercial vessels are fitted with autoalarms. The autoalarm is placed in operation when the radio operator is not on watch while the ship is at sea. If the alarm is sounded, bells will ring on the bridge, in the radio room, and in the radio operator's cabin. This alarm responds to the alarm signals sent by a vessel in distress.


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