Chapter 1. Mission of the Communication Course 321
Chapter 2. Security 322-323
Chapter 3. Visual Communications and Code 324-326
Chapter 4. Recognition Signals 327
Chapter 5. Radio Voice Procedure 328-329
Chapter 6. Operation and Description of Radio 330-333
Chapter 7. Electrical System 334-339
Chapter 8. Radio Direction Finder 341-345
Chapter 9. Communications procedure 346-354
Chapter 10. Internal Communications 355-356



The mission of the course is to qualify all students in the following:

  1. Standing proficient communication watches.

  2. Thorough understanding of rules and principles of security.

  3. MTB standards of visual (blinker and semaphore) and code communications.

  4. Operating and maintenance--knowledge of communication and electrical equipment on board.

The degree of proficiency and the amount of knowledge in communications expected of students will depend to some degree on the student's rating. For example, it is intended and expected that officers and radiomen should learn more than a ship's cook and the instruction is designed to give officers and radiomen a more advanced course; however, all other ratings must meet certain minimum requirements in order that a satisfactory standard of communication efficiency may be maintained in operating squadrons.


Chapter 2. SECURITY

Security is the protected condition of naval subjects which prevents or hinders the enemy getting certain information which would be of military value to them.

Inadequate or faulty security of certain information can directly cause battles, ships, and lives to be lost; that is why proper security is so important and necessary.

Study the following rules which will preserve security. After you have studied them, remember to practice them at all times.

A. Make it your policy never to discuss naval or military matters on the beach.

B. Do not reveal naval or military information to your friends "confidentially" or otherwise. Resist the temptation to get attention by putting out "inside'? information. Your friends and relatives, as well as strangers, will naturally be curious to know about motor torpedo boats because they are new, different, and spectacular, and it will be your duty to politely but firmly divulge nothing. Remember that their interest usually is idle curiosity, and no good can come from answering their questions; there is a good chance that a great deal of harm may result.

C. The following are subjects which the enemy would be particularly interested in knowing--for this reason be particularly careful about guarding their security:

  1. Dimensions of the boats.
  2. Their speed.
  3. Their seakeeping qualities.
  4. Their cruising range.
  5. Their offensive and defensive power.
  6. Their armament.
  7. Their engines, propellers, and shafting.
  8. Their complement.
  9. Future plans and employment.
  10. Tactical doctrine.
  11. Communication facilities, procedure and frequencies.
  12. Disposition and location of various squadrons.
  13. Number of men in training.


  1. Number of new boats being built and plans of construction.
  2. Means of getting boats from one place to another.
  3. Ships present in harbor, movement of ships, supplies and task forces, reports from friends on battles and engagements.
  4. Unusual events, liberty rules, watches, duties.

D. Do not let military information slip out over the radio. For example, do not disclose speeds, frequencies, recognition signals, codes, whereabouts of boats, etc. Do not "jabber" over the radio. Use standard voice procedure so as to avoid circuit peculiarities. Avoid unnecessary testing and talking over radio. When practicable use visual communication instead of radio.

E. Take every step within your power to guard "classified" matter. There are three types of classified matter. They are:

1. Secret. --Secret matter is the most highly protected classification. Compromise of secret matter might endanger the national security.

2. Confidential. --Confidential matter is the next highest category after secret. Compromise of confidential matter might be prejudicial to the interests and prestige of the Nation.

3. Restricted. --Restricted matter is of such a nature that it's disclosure should be limited for reasons of administrative privacy.

Classified matter on each boat must be properly safeguarded. Secret and confidential codes, charts, letters, recognition signals, operation orders, etc. , must be kept locked up when not in use and handled always with strict accountability. A boat must never be captured with classified matter still on board. It must ut all costs always be thrown overboard or burned.

The compromise of a code or recognition signal may cause many other ships using the same code and signals to fall unsuspectingly into the hands of the enemy.

F. See that your shipmates or friends or relatives do not compromise security. Do not sit idly by while vital information is passed about. Stop such carelessness tactfully if you can; if you can't, stop it by any method that will work.

G. Do not lose your notebook or leave it lying carelessly around. The enemy has brought the war behind our front lines; we must fight him there as well as at the front. Practice security of naval and military information at all times.



No student will be considered qualified in communications until he can meet the following standards in semaphore, blinker, and code:

  Words per minute
Semaphore Blinker Code
Officers 8 8 10
Radiomen 8 8 20
Quartermasters 10 10 10
Others 6 Alphabet Alphabet

Some systems are more helpful than others in learning semaphore, blinker, and code, and these will be demonstrated in class. However, success is probably 90 percent sweat and 10 percent the system.

Students should use every opportunity to develop their signaling to the point where they can at least meet the above requirements. Classrooms are available at night for practice and study at blinker and code. Semaphore flags can be had by drawing them from the communication office.

For many students the number of classroom hours available for signaling drill will be inadequate. These students must make this up by drill on their own outside the classroom.

Students must familiarize themselves with the following principles used in flashing light (blinker) and semaphore:

Flashing light.--The senior officer embarked in a ship is considered to be the originator of a message unless indicated differently. When using multiple call signs, the responsibility of seeing that other ships get a message lies with the ships lying between the originator and the addressees. In using individual call signs a ship does not relay unless the preamble requires it.


In situations in which answering might reveal the location of naval units, the originator makes "N N N" on a blinker tube (which means do not reply) and then sends the message twice-- thus avoiding disclosure of light in all but one direction and making reasonably sure that the message gets through.

In flashing light procedure, the person receiving gives a short dash after each word received. The sending station should repeat a word until the receiver indicates that he has received the word correctly by giving the short dash. "B," is used to show receipt of a message.

On MTB's, flashing light signals are sent by searchlight (day) , by blinker tube (night) , and by MP (multipurpose) light (day and night). The MP light is probably the best for all round blinker signaling on the MTB's. The method to use in transmitting by flashing light depends upon the particular circumstances at the moment. The number of addressees and their position relative to the originator, the degree of security desired, and the degree of rapidity desired are all factors to be considered. A point to be remembered in connection with this is never to use a high-power system when a lower powered one will suffice. Semaphore should always be used wherever practicable for reasons of security. To illustrate, even the flashes of directive flight may be seen from an aircraft too far away to be seen from surface vessels.

When using flashing light of any kind during daylight hours, or directive light at night, always ascertain that your light is training directly upon the receiving station as though you were trying to illuminate him. If during the transmission, the receiving station makes "W," it means that your light is improperly trained or that it is too weak to receive. In this case make sure that the light is trained properly and is level. If the receiving station continues to make " W," the transmitting station must shift to a higher powered system.

Semaphore.--In sending semaphore always stand erect, feet together, with arms straight. Endeavor to make the characters plainly with a distinctive pause between characters. Always watch your arms, not the receiver, in order to check yourself. When making characters such as "I," "O," "H," "X," and "W," the pivoting of the body at the waist allows these letters to be made more clearly. Never permit your hands to. curl


around the body. Pretend that you have no elbows and keep your arms parallel. Avoid stiffness. A relaxed attitude is best as it is not tiring for long messages.

There are special signs (prosines) used in semaphore. They are:

The answering sign.--Used to answer a caller, when condtions affecting the receiving and sending are bad, to show that a word or item has been received.

The attention sign.--To call a ship or gain attention.

The front sign.--Used before and after each call sign, word, code group, other procedure sign, and between letters of a code group.

The numeral sign.--Used before and after each group of numerals or combinations of numbers and letters in the text.

The semaphore sign.--"SEM" made by flashing light to indicate that semaphore will be used thereafter.

The visual space sign.--Double "I" used to separate code group.

Move signs.--Used in cases where the sender has chosen a poor background, making it difficult or impossible for the receiver to catch the message. These signs are:



Recognition signals are used between vessels (and aircraft) to determine mutual identity, i.e., whether friendly or enemy.

Recognition signals are composed of (a) the challenge, and (b) the reply. These signals are usually made either by flashing light, by smoke bombs or flares. Very's stars and flares are usually used in emergencies when flashing light has failed for one reason or another.

Recognition signals must be on every boat before getting underway. These signals are confidential and must either be returned to the Communication Office or destroyed by burning when defunct.

Always observe the following rules with regard to recognition signals:



Students should practice radio voice procedure between themselves until they have become familiar with it and it has become second nature. Normally, any embarassment or self-consciousness will be overcome by this sort of practice and when students actually talk into the microphone they will already have gained confidence in themselves.

The following is an illustration of standard voice procedure:

Supposing the PT 61 wants to call the PT 62, the 61 operator says:

"2 from 1 answer"

and the PT 62 operator comes back with

"1 from 2 go ahead."

(Note that the number of the boat being called comes first and that of the caller last.)

The PT 61 operator then gives the message:

"2 from 1" (message) "go ahead."

The PT 2 operator then acknowledges by the following:

"1 from 2 Roger."

Roger means "I have received your transmission." If the PT 61 had given the PT 62 an order, the operator would inform the boat captain and the latter might instruct the radioman to answer with a


which means "I will comply. "

If an operator wants to tune his receiver, he can call a boat and ask for a "long" or "short test count. " A "short test count" is from 1 to 5 and back to 1; a "long test count" is 1 to 10 and back to 1.

If a radioman wants to know how he is being received he may ask another boat

"How do you receive me?"

and if the answer is:

"I receive you strength five"

this signifies the reception is good. Strength four down to


strength one represents less satisfactory degrees of reception in that order.

When speaking over the microphone do so clearly and distinctly, holding the instrument close to your mouth. Do not shout. Enunciate clearly.

Never say please or thank you on the radio. Never engage in unofficial transmissions. Keep testing and traffic down to a minimum. Be careful not to give away confidential information in talking over the radio.

Radio silence is a condition where absolutely no radio transmissions are permitted. Breaking radio silence is a serious offense.

Radio operators must not send transmissions unless authorized to do so and they must report all transmissions to the boat captain immediately upon receipt.

While it is often convenient to stand radio watches on the loudspeaker, the radio watches should be stood by earphone as weak receptions may not be heard on the loud-speaker.

It is good practice to use "Z" signals whenever possible. "Z" signals are abbreviated signals for certain frequently used messages and they are found in the communication procedure book located near the radio. Students should familiarize themselves with this book.

A complete radio log will be kept at all times and an entry made at least every 5 minutes. Below is an example of a typical radio log.

Date____________________ 19____
U.S.S. (name of ship or station)

G. C. T.)
Call Remarks


Chapter 6. THE RADIO

You should memorize the following data about the radio:

Name.--Navy Model TCS radio telephone and telegraph transmitter and receiver.

Frequency range.--1. 5-12. 0 megacycles (1,500-12,000 kilocycles).

Output.--40 watts Key/CW; 20 watts voice.

Power supply.--Two dynamotors.

Antenna.--Whip type--20-foot vertical.

Instructions for Operating TCS Radio

See that "Radio" switch in engine room is in the ON position. The whip antenna should be in the fully extended position at all times while the radio is being used for receiving or transmitting.


1. Set "Band Switch" on appropriate band position.

2. Set "Oscillator Selector" in correct position (Generally "M. O. ").

3. Set "Tuning" control, using proper scale.

4. Set "RF gain" and "AP gain" controls to about position 5.

5. Set "Voice-CW" switch to type of signal being received.

6. Turn "Power" switch ON.

7. After set has "warmed up" readjust "timing" control if necessary, and adjust RF and AF gains for good signal volume.


1. Set "Band Switch" on appropriate band position.

2. Set "Tuning" control to correct frequency. (When using first band, use direct reading. When using second band, divide frequency by two and put result on dial. When using third band, divide frequency by four and put result on dial.)

3. Set "Oscillator Selector" to correct position. (Generally "M. O. ")


4. Place "Emission" switch on Voice or CW as desired.

5. Plug in Key or Microphone as required.

6. Set "Plate Tuning" on "0", "Coupling" on "5", "Ant. Cond. " on OFF, "Loading Coil" on "0", and Antenna Loading on "O".

7. Put "Power" switch in ON position and let equipment warm up for about 20 seconds before proceeding.

8. Press Microphone button (or hold Key down) and with other hand turn "Plate Tuning" to right slowly until "Plate Current" meter needle dips to a minimum point.

9. Turn "Antenna Loading" control to the right until a maximum reading is obtained on the "Antenna Current" meter.

10. Check the reading of the "Plate Current" meter; if it is above the first red mark (when using voice) , decrease it by decreasing the "Coupling" control. If using CW, reduce current indication to slightly below the second red mark, using above method.

11. If operating on band 1 and no reading is obtained on the "Antenna Current" meter after carrying out above steps, set "Loading Coil" to position 3, further adjusting it to the position where the greatest "Antenna Current" reading can be obtained.

12. When using the third band, if no indication can be obtained on the "Antenna Current" meter, shift "Ant. Cond. " to "Series" and then readjust "Antenna Loading" control, if still no indication set "Ant. Cond. " to "Parallel" and again readjust "Antenna Loading. " One of the 3 positions will be the correct one, and this can only be determined by test.

Remote Control

1. Make all adjustments to receiver and transmitter as given above.

2. Set "RF gain" at 5, and "AF gain" at 10 on receiver.

3. Set "Power" switches on receiver and transmitter to OFF.

4. Insert Microphone (and headphones if desired) in proper jacks in control unit.

5. The receiver and transmitter may now be started and stopped by use of the switches on the control unit. Also the volume of the incoming signal may be adjusted by means of the "Volume" control on the remote control unit.


Location of Faults

Receiver.--Receiver motor generator set will not start:

1. Battery switch in engine room power distribution panel not on RADIO position.

2. Battery fuse on engine room power distribution panel open.

3. Interlock switch open in receiver.

4. Fuse open in motor generator mounting base. Receiver motor generator set will not turn off at receiver: (a) Receiver POWER ON--OFF switch in ON position at remote control unit.

Receiver motor generator set will not turn off at remote control unit: (a) Receiver POWER ON--OFF switch in ON position at receiver.

Steady howl in receiver when tuned to transmitter frequency: (a) Transmitter OSCILLATOR SELECTOR switch in MO TEST position.

Unable to hear boats in company and able to hear distant base station: (a) Receiver RF GAIN advanced too much, causing local loud signal to block receiver completely.

Transmitter.--Receiver motor generator operating but transmitter motor generator will not start:

1. Interlock switch open in transmitter unit.

2. Fuse open in motor generator mounting base. Transmitter motor generator set will not turn off at transmitter: (a) Transmitter POWER ON--OFF switch ON at remote control unit.

Transmitter motor generator set will not turn off at remote control unit: (a) Transmitter POWER ON--OFF switch ON at transmitter.

Notes on the Operation of the TCS Radio

Further instructions for tuning.--When motor torpedo boats are operating together as a unit, experience has shown that difficulties are experienced in radio communication between boats of the operating unit and also between the boats and the base or tender from which they may be operating. These difficulties are experienced even though all boats may have their transmitters and receivers "tuned" to the same frequency. The word "tuned" is used advisedly, for it has been found that personnel are superficial in setting up their transmitters and receivers and because


of this all boats are not operating on the same frequencies. A difference of only a few kiloycles in the tuning of one boat can cause breakdown of radio transmission and reception. Whereas, under most circumstances, the radios are operated on crystal-controlled frequencies, even then differences great enough to hamper communication may be experienced.

A small amount of care and effort in originally setting up and tuning the receiver and transmitter will pay dividends in the long run. All boats should tune their receivers carefully to the exact frequency being used by the senior boat or the base. Calling the senior boat or base before getting under way and definitely making sure that all transmitters and receivers are on the exact frequency is the best way to do this. A method of doing this is for the senior boat to "zero beat" his receiver with the transmitter of the base or tender and then to "zero beat" his transmitter with his receiver. All other boats should then check their frequencies with the senior boat. In this manner the senior boat will be on the exact frequency of the base or tender and all boats will be on the same exact frequency, having checked their equipment prior to getting under way. (The "zero beat" method will be demonstrated in the boats.)

Radio watches must be stood with the headphones. It is the poorest kind of radio procedure to stand a loudspeaker watch. The loudspeaker exists merely for the information of the boat captain. It has sometimes occurred that boats have stood radio watches on the loudspeaker, with the volume turned to a position where the signal being received from the boats in the immediate vicinity is received at a comfortable loudness. The signal of a station calling the boats, then, from a great distance would not be audible over the loudspeaker and communications would break down.




1. The primary electrical system is a 24-volt direct current installation which is fed by storage batteries and generators. It is a two-wire system employing a grounded negative return; i.e., the negative side of each circuit is connected to the ground system and to each other. This method of wiring is employed so that the voltage of all circuits will be of the same value, regardless of their location in relation to the batteries, thus effectively eliminating any effect which might be caused by the resistance of a conductor.

2. The system is divided into two subsystems known as the "Battle" and "General" systems. When the "General" system is in use, all of the power, white lighting, and navigation circuits may be used. When the "Battle" system is in use, all of the power and only the battle lighting circuits may be employed.


The storage batteries are located in the engine room and consist of two banks of 24 volts each. Each bank is composed of two 12-volt, 150-ampere-hour capacity batteries, connected in series so as to furnish 24 volts at 150 amperes per hour. These batteries are of the common lead-acid type, especially constructed for durability. The two banks are known as battery No. 1 and battery No. 2.


As the electrical system depends on storage batteries for its energy, some means must be provided to recharge these when their energy has been exhausted. This is accomplished by electrical devices known as generators, which convert mechanical energy into electrical energy in quantities sufficient to renew the strength of the batteries.


Four generators are provided. First, the one of the largest capacity which is known as the auxiliary generator. This machine is a gasoline-driven, air-cooled device, capable of delivering 175 amperes of current at 28. 5 volts, or 5 kilowatts. Second are the three main engine generators, each of which is connected to the shaft of one of the Packard engines. These three generators have a capacity of 75 amperes at 28 volts each.

The auxiliary generator performs a function other than that of charging batteries in that it is used to furnish the additional power required for certain electrical machines on the boat beyond the capacity of the batteries.

Voltage Regulators

As the voltage of generators varies with their speed and since we must have a constant voltage of a certain value (28. 5 volts) , we employ a device known as a voltage regulator. This machine is appropriately named in that it regulates the voltage of the generator to a certain value. Each of the four generators has its own independent regulator.

Distribution and Control

In the engine room is an electrical distribution and control board. This board or panel has many electrical cables from all parts of the boat running into it and is equipped with various switches, relays, and indicating meters. It is used to distribute the electrical energy from the batteries and generators to various parts of the boat and various electrical machines in the amounts required. The meters indicate where the electrical power is coming from, going to, amount and condition of.

Forward, in the chart house, is a secondary panel board to be used in conjunction with the one in the engine room. On this panel are switches for controlling the navigation lights, signal buzzers, and a system selector switch, to select either the battle or general system (if installed).

The electrical current is conducted to various parts of the boat by means of various-size cables, which are for the most part run through conduits. These conduits are both round and square of various sizes, dependent on the number of cables running through them.


Junction boxes are located at frequent intervals along the conduits. All conduits are, or should be, watertight and gas-tight. Where the conductors are outside of conduits, they are covered with a metal braid called shielding and all connections to fixtures are watertight and gastight.

All switches and fixtures throughout the system are of the enclosed, gastight type.

Power Machinery

The electrical devices requiring a large amount of power in excess of the capacity of the batteries are only two in number and will be operated only from the auxiliary generator singly NEVER AT THE SAME TIME AND NEVER DIRECTLY FROM THE BATTERIES. These are the air compressor (if installed) and the galley range.

Fuses and Circuit Breakers

All electrical circuits are protected from overloading by fuses or circuit breakers. They are located in several boxes throughout the boat and are of various electrical and physical sizes.

Vent Blower Motor

Air is forced through the boat's ventilating system by means of a fan attached to an electric motor of one-half horsepower capacity. This motor is located in the armory. It consumes approximately 15 amperes at 24 volts, thus necessitating power additional to the storage batteries if the blower system is to be operated for a long period of time.

Galley Range

The heating units of the galley range draw large amounts of current. It requires approximately 63 amperes at 24 volts. It is NEVER operated from the storage batteries alone. This high current must be supplied by the auxiliary generator or the three engine generators working at maximum capacity.


Gas Alarm

The gas alarm is an electrical instrument, employed to take samples of air from either the engine room bilges or the tank compartment and measure its gasoline vapor content. If the air is found to be of sufficient gaseous content, the device automatically lights a red -warning light and sets a siren into operation.

Storage Batteries

Storage batteries are devices employed to store electrical energy in a convenient manner until ready for use. They are designed to withstand severe usage over a period of many months with intelligent care. Certain laws must be observed in order to obtain this long, faithful service. These laws are few and can readily be applied by anyone in the naval service, regardless of their electrical knowledge. They are:

  1. Do not attempt to work the battery over its rated capacity.

  2. Do not charge or discharge beyond normal limits.

  3. Keep plates covered by approximately one-quarter inch of electrolyte.

  4. Keep battery tops dry and clean.

  5. Do not allow battery to stay in a discharged condition.

  6. Keep batteries well ventilated.

  7. Keep battery terminals lightly covered with a good grade of grease (preferably vasoline).

  8. Keep battery connections tight.

As the electrolyte in a storage battery gives off a highly explosive hydrogen gas under certain conditions, the following precautions, in addition to the maintenance rules above, must be observed.

  1. Keep temperature below 115° F. at all times.

  2. Allow no open flames or electric sparks near the battery.

  3. Keep metal tools from the vicinity of the battery, as they might fall across the battery terminals and produce an electric spark.

  4. Keep cell covers on batteries at all times except when taking samples of the electrolyte or adding distilled water.

  5. Keep battery well ventilated, especially during charge, in order to dissipate the hydrogen gas into the atmosphere.


The state of charge of a storage battery is determined by means of a battery test set known as a "Hydrometer. " This device measures the specific gravity of the electrolyte, which is proportionate to the state of charge. For the type of battery used aboard the PT boats this is 1. 275 for a fully charged cell. When this reading drops to 1. 200 the battery should be recharged. These readings are considered at 80° F. and must be corrected for other temperatures. The battery test set includes a calibrated thermometer to facilitate this.

Bonding System

The rapid movement of a PT boat through the water causes considerable friction. As friction is the producer of static electricity, then a PT boat becomes quite a storehouse for this electrical charge. The electrical charge is of extreme danger when in the immediate vicinity of gasoline or its fumes, as a tiny spark caused by it may result in an explosion of sufficient force to destroy the boat. In order to control this electrical charge and pass it off safely to the earth, every piece of metal of appreciable size and every frame of the boat are electrically connected to one another and finally to a ground strip of copper along the boat's keel. The water under the keel acts as an electrical conductor to the earth, thereby allowing the static electricity to pass harmlessly to the earth via a path of low resistance.

The elimination of sparks caused by static electricity also cuts down interference in radio reception aboard the boat.

Auxiliary Electrical System

An auxiliary electrical system for use when at a dock has been installed. It is operated by 110 volts A. C. and is used for lighting, cooking, and heating. It serves only the portion of the boat forward of the chart room. It is connected to the shore line by means of a portable cable carried aboard the boat. The system is designed to consume a maximum of 100 amperes at 110 volts. All fuses for the entire system are located in a fuse box inside the steering chain locker in the wheelhouse. This system has its own independent wiring and lighting fixtures.



The greatest factors in maintaining any electrical system are frequent and thorough inspections. It is much easier to prevent a casualty than to repair the damage after the casualty has occurred. These inspections should be conducted immediately after the boat has returned to its base after being underway for any length of time. The following points should be noted:

  1. See that all electrical connections are tight.

  2. Note condition and state of charge of the batteries.

  3. Inspect all electrical conductors for breaks in their outside shielding.

  4. See that all switches work properly.

  5. Replace any burned-out fuses, after determining the reason for the fuse being burned out, and correcting the abnormal condition.

  6. See that all electrical fittings are in good condition.

  7. Inspect the bonding system for any loose connections or breaks.

ALWAYS REMOVE THE VOLTAGE FROM ANY CIRCUIT WHILE REPLACING A FUSE IN THAT CIRCUIT. When in doubt, turn all switches on the engine room panel board to OFF.

Carry at least 300 percent spares for all sizes of fuses and 100 percent light bulbs used aboard the boat.



The Purpose of a Radio Direction Finder on a PT Boat

The radio direction finder on a PT boat is used to get radio bearings on radio signals. These bearings, like those taken with a pelorus, are used to help determine the position of the boat. I The R. D. F. is particularly useful when navigating out of sight of land and in fog.

Location of the R. D. F. in the 77-foot PT's

The R. D. F. in the 77-foot boats is located in the wheelhouse on the starboard side.

Specifications of the R. D. F. Used in the 77-foot PT's

Name.--Bludworth Standard Arrow.

Frequency range.--280 to 520 kilocycles.

Current supply.--Independent six-volt storage battery charged from the boat's 24-volt circuit.

Antennae.--(a) Rotatable loop located on the starboard side of cab.
(b) Small vertical "whip" located on port side of cab.

Operation of the R. D. F. Set (Bludworth)

Step 1.--Insert headphone plug in phone jack.

Step 2.--Turn battery charging switch to "off" position.

Step 3.--Turn set on by turning masterswitch to "on. " Adjust volume (volume control knob).

Step 4.--Set tuning dial to frequency of signal station desired.

Step 5.--Rotate loop wheel until minimum signal is heard. (a minimum is the point of weakest signal just before a point of silence or null).

Step 6.--Adjust "balance" knob until as sharp a null as possible is obtained.

Step 7.--If the boat is lost and the operator is not certain which side the signal is coming from he will use the sense feature. (It must be realized that radio signals are bilateral, and that if


there is a null of 090°, there will also be one at approximately 270°, etc.; therefore, the operator must either know or determine which side the signal is coming from.) To operate the sense feature, turn the short red pointer, marked with an "S", to the bearing on which there is a null. Depress sense button and listen to signal. Then turn the "S" pointer approximately 180° to the reciprocal bearing. Depress sense button and listen. The bearing on which the signal is loudest will indicate the side from which the signal is coming.

Step 8.--Before a fix can be gotten, it is necessary to get at least two bearings by a repetition of the procedure ju^t outlined.

Operation of Radio Direction Finder
Model DAE

A. Steps

    1. Turn power switch to ON position.
    2. Plug in headphones.
    3. Unlock loop.
    4. Turn dial light switch to ON position, if illumination of tuning scale is desired.

  1. Band Switch:

      Band 1--240 to 520 KC.
      Band 2--480 to 1050 KC.
      Band 3--970 to 2000 KC.
    1. Place band switch in position 1, 2, or 3 as required for the desired frequency band.

  2. Advance Volume Control clockwise as required.

  3. Turn on BFO switch to obtain high pitched tone most convenient for taking bearings. Place "Balancer" on O.

  4. Tune in desired signal with tuning knob. Readjust volume control, if necessary, and rotate loop handwheel until signal is clearly heard and identified.

  5. To take bearing rotate loop to obtain minimum value of signal, adjusting the Balancer Control to the right or left of O position to sharpen bearing. Correct bearing is NO SIGNAL or NULL position. Use relatively high volume while at or near "NULL" position of loop and balancer.


  1. After bearing has been obtained from azimuth scale, refer to calibration chart for corrected bearing, noting frequency band or frequency listed on calibration chart.

  2. If general direction or. SENSE of incoming signal is not known, the following must be done after the bearing is taken: lower volume and turn Balancer so that pointer is at SENSE position and hold it in that position against tension. Then rotate the loop several degrees (i.e. about 20°) towards lower readings on the scale and observe whether the signal increases strength. If so, the bearing is correct. If not, the reciprocal of the bearing is correct.

  3. When securing unit, turn power switch to OFF position. Lock loop with hand brake.

Plotting Radio Bearings

The following procedure is standard for plotting R. D. F. bearings.

1. When the R. D. F. operator gets a null,, he calls out "Mark" to the helmsman and notes the time,

2. The helmsman calls down the boats heading (reading directly from the magnetic compass) to the R. D. F. operator.

3. The R. D. F. operator then relays the following information to the navigator:

  1. Time of bearing.
  2. Station.
  3. Corrected D. F. bearing.1
  4. Ship's head.

Since the bearings gotten on the R. D. F. are bearings relative to the boat's keel, they must be converted to bearings relative to the ship's heading magnetic. To do this the navigator simply adds the R. D. F. bearings to the boat's heading as read from the magnetic compass. If the sum is greater than 360° the navigator subtracts 360°. The navigator will then correct this bearing for errors of deviation, variation, and, if the station is over 50 miles

1Corrected bearing: The bearing corrected for the deviation which is caused by large masses of metal and closed loops in the vicinity of the direction finder loop antenna.


away, for mercator distortion, using the proper table in H. O. 205. The resultant corrected bearing will then be a true bearing and can be plotted on the chart as such.

It must be remembered that a fix from R. D. F. bearings gives only an estimated position and as such, therefore, should be marked "E. P. " The D. R. track line is not replotted from a radio bearing fix.

Radiobeacon Stations

The sources of signals which are used by R. D. F. 's on PT boats are. radiobeacon stations and light vessels. Each PT should have on board Hydrographic Office Publications 205 and 206, which list all radiobeacon stations and light vessels of the general area in which operations may be expected. Radiobea-cons are indicated on all charts by O in orange. These stations maintain published schedules during clear weather and operate continuously during periods of poor visibility. In general, the beacons transmit modulated, interrupted continuous wave (MOW) identifying signals of long and short emissions. Those on the coasts of the United States employ very simple signals of one characteristic and the beacons are generally arranged to operate in groups of three, on the same frequency, so as to permit taking three point bearings in rapid succession from three, different transmitters. For instance, at and near the entrance to New York Harbor are Fire Island Light Vessel, Ambrose Light Vessel, and Barnegat Light Vessel. Fire Island transmits 1 minute and is silent 2 minutes; Ambrose the next succeeding minute after Fire Island and is silent 2 minutes; Barnegat the next succeeding minute after Ambrose and is silent 2 minutes; it is evident, therefore, that during the period of transmission, bearings may be taken on three light vessels successively within 3 minutes. During clear weather most groups of three beacons transmit in the order described for two 10-minute periods of each hour. Each hour is divided into 6 periods of 10 minutes each. Period 1 is from the hour to 10 minutes past, etc.

Calibration of the R. D. F.

Magnetic forces which exist in each PT have a disturbing influence on incoming signals. This influence will cause bearings


to be wrong by plus or minus so many degrees. The purpose of calibration is to determine what this error is throughout the R. D. F. compass rose. Briefly this is done by comparing R. D. F. bearings of transmitting station with bearings taken by pelorus. The comparison will reveal plus or minus errors on various bearings which can then be worked into an R. D. F. error table. With this table at hand, corrected R. D. F. readings can be given the navigator. The Bludworth R. D. F. has a mechanical automatic compensator needle which, when properly adjusted to the various errors, will automatically correct the indicator needle so that reading can be direct. The calibration of an R. D. F. on a PT requires considerable preparation and understanding; therefore, it is suggested that PT officers, radiomen, and quartermasters study up on this work by reading paragraphs 30-55 of chapter 30 in M. E. I.

General Remarks

Due to a phenomenon known as night effect, in general, Ri D. F. bearings taken at night, sunset, and sunrise, should be regarded as of doubtful accuracy. For further explanation Of "night effect," consult M. E. I., chapter 30-101.

Operation of the R. D. F. on PT's is not difficult. However, patience and practice are necessary before a new operator will gain confidence and proficiency.



Communication procedure is the correct method whereby naval communications are conducted.

Naval communications are in the following forms:

(a) Letter.--A communication in writing generally expressed with some degree of formality and transmitted by physical transfer in the original state.

Example.--None necessary.

(b) Mailgram.--A communication expressed in brief form and transmitted by physical transfer usually in the original state.


(c) Message.--A communication expressed in brief form and transmitted by special means to hasten its delivery. The term embraces dispatches, signals, and procedure messages.


It must be remembered that the science of communication procedure cannot be reduced to a few pages and a complete description of the subject is beyond the scope of this book. Officers, radiomen, and quartermasters should refer to communication instructions for guidance. The points covered below are only the more elementary and are designed to familiarize students with the general scope of the subject.

Procedure Signs--Procedure Signals

Procedure signs (prosines) are single letters or characters, or combinations thereof; i.e., CTZ AR VA, etc. Procedure signals (prosigs) are three letter prosines with "z" as the first letter, i.e., ZMA, ZTE, ZCE PROSINES and PROSIGS have certain definite meanings, such as frequently used orders, instructions, requests, reports, etc., and are used to conduct communications more rapidly and accurately. For example, the following is a complete list of PROSINES:

AA   All after.
AA   Blank.
AB   End of transmission.
AS   Wait.
B   More to follow.
C   Correction.
CC   Corrected version follows (used in signals).
D   Deferred.
E (8 or more)   Erase--Error sign.


F   "F" method, do not receipt for.
GR   Group count.
H   Hold for delivery until called for.
IX   Execute. To follow.
IX   Execute. (At termination of 5-second dash.)
IMI   Repeat
J   Verify and repeat.
K   Go ahead, transmit.
KK   Parentheses.
L   General relay sine.
N   Exemption sine.
NR   Serial number.
O   Urgent.
OP   Operational priority.
P   Priority.
Q   Information.
R   ROutine and receipt
S   Signal strength.
T   Specific relay sine.
V   From.
VA   End of schedule.
W   Interference
XE   Slant sine
Y   Acknowledge.
Z   Originator.

Procedure signals are listed in the communications procedure book.

Parts of Message

All naval dispatches and messages are made up of three general parts: Heading, text, and suffix.

(A) Heading

The heading is composed of four parts, namely, the call, preamble, address, and prefix.

The call is used to establish communications and is made up of the call sign of the station called followed by the prosine "V" meaning "from," and the call sign of the calling station.


The preamble immediately follows the call (or call up) and contains routing instructions, appropriate prosines, and the calls of the stations to whom or by whom the dispatch is to be relayed or delivered.

The address in general shows by whom the dispatch was originated and to whom it is to be delivered. More specifically the address sometimes contains addresses for whom the message is only passed for information. Should the dispatch not be intended for some addressees within a collective address, these addresses can be exempted by use of an appropriate prosine. The address also contains the date and time group which is the reference number. The first two digits give the day of the month and the last four digits give the G. C. T. time which is generally the time of origin.

The prefix is that part of the heading containing the precedence of the dispatch as well as the group count of the text. Included in the prefix are sometimes instructions for addressees to acknowledge the dispatch.

Examples of calls (or call-ups)--

Examples of preambles (underlined):

Examples of address (underlined):

Examples of the prefix (underlined):


Example of heading.--

(B) Text

The text contains the idea or information which the originator desires to convey to the addressee (S).

(C) Suffix

The suffix is always a prosine or combination thereof and/or call signs. As all transmissions must end with a prosine or a combination thereof, this is known as the suffix.


Executive method.--In order to make up signals that"will be executed at certain time or upon signal, the "execute to follow" signal is used. The execute to follow prosine is IX and its use is illustrated in the following examples:

This shows that the dispatch will be acted upon when the controlling or originating station "executes" the signal. When the originating station is ready to execute the signal, he makes the following: 3 V 7 IX (5 sec.) k. Upon cessation of the 5-second dash the signal is executed.

NONT.--The voice procedure equivalents to the above examples are:

and then:


Three types of communication procedure are:

(a) Normal procedure.--In this method a transmitting station calls the station for whom the message is intended and delivers it. However, as is often the case, the addressee is not in direct communication with the originating station when it becomes necessary for the message to be relayed by other stations. Stations which usually handle much relayed traffic are generally shore stations who send schedules and clear great amounts of this traffic. Normal procedure always includes a time and date group and a group count.

(b) Abbreviated normal procedure.--When the addressee and the originator are in direct communication, the call-up may serve as the address, e. g., NEKT V A3U 022300 P GR 22, etc. In this example NEKT is to take action on A3U's dispatch. In abbreviated normal procedure NEKT can receipt thus: V NEKT R. For since NEKT is in direct communication with A3U it is permissible to drop the call sign of the station called since this is understood.

(c) Abbreviated procedure.--Abbreviated procedure is readily recognized by the omission of one of the following things in the heading: The date group, the time and date group, or the group count. Example: C5L V A3U BT _____. In this example the time and date group and the count have been eliminated. (Note. It is desired to use at least the time group whenever possible for easy reference to the dispatch.)

Prosines used to indicate precedence of naval dispatches are:

1. "O". This prosine means the dispatch is of "URGENT" precedence and must be treated with the utmost speed possible. A maximum delay of 5 minutes is permissible in taking action. The urgent prosine is used with contact reports, or contact signals when the enemy has been sighted or contacted and/or in dispatches about contact.

2. "OP"--Operational priority.--This prosine ranks immediately below the urgent precedence in matter of speed of action required. Its use is confined to dispatches relating to operations of Fleet units.


3. "P"--Priority.--Denotes a precedence allowing a maxi-imum of 20 minutes in handling or taking action on a dispatch-bearing this prosine.

4. "R"--Routine.--This classification of precedence is for dispatches which require only normal speed in handling. In the use of routine precedence the prosine "R" is usually omitted and the absence of any prosine indicating precedence is assumed to mean routine.

5. "D"--Deferred.--The lowest precedence assigned to messages in normal naval form is called deferred, and indicates a delay in action can be allowed until the beginning of office hours on the morning following the origin of the dispatch. Office hours are arbitrarily assumed to be 0800. The prosine "D" is usually assigned to messages of lesser importance.

Call Signs

1. General.--There are two main types of calls, namely, radio and visual.

2. Radio call signs.--(a) Three-letter calls of which the first character is the letter "N" are assigned to all naval shore radio stations.

(b) Four-letter calls of which the first character is the letter "N" are assigned by international law to all naval vessels. This call, in addition to being their radio call, is also their INTERNATIONAL CALL.

(c) Four-letter call signs which are pronounceable, such as MUSK, PAUK, etc., are assigned geographical locations, offices ashore having no radio communications, geographical areas, and groups of any of the aforementioned; offices having no radio and Naval activities without radio.

(d) Call signs made up of letter-numeral-letter combinations are assigned to commanders of fleet or ship units, to groups of commanders, and to groups of ships. These calls are known as collective calls.



(e) Means are provided for encrypting any of the above calls.

(f) Secret calls of various combinations of characters can be compounded for use with all ships, stations, and offices.

(g) For information on tactical calls, see section (e) under "Visual Call Signs. "

3. Visual call signs.--(a) General.--There are three types of visual calls, namely: Ship, commander, and collective calls, the latter consisting of combinations of the former two types.

(b) A ship's call consists of the ship's class call letter and her call number in one, two, or three digits. All vessels and aircraft are assigned a class call letter to indicate the type. For example, B stands for battleships, R for aircraft carriers, D for destroyers, etc.

(c) Collective calls consist of the letter "F" and a numeral designating a specific group. By placing the letter "F" between the numerals, the commander of that group is formed. To illustrate, 22 stands for Battleforce (F22) and the. commander battleforce call is made by inserting the letter "F" between the two numerals. Thus we get 2F2. To illustrate further, "AP" means transports and "F7" means Base Force. Then APF7 is the call for transports of the Base Force.

(d) When it is desired to call a type commander of a fleet or force, the complete call is formed in this manner: place the class letter of the type designated and the alphabet letter "F" between the two numerals of the organization. For those calls below "10" the numeral "Zero" is used as the first element of the call sign.

(e) Tactical calls.--Different task forces of the fleet are assigned numerical task forces, groups, or units. A letter is provided for commander and collective calls, and which letter of the alphabet is used depends upon the geographical area in which the fleet is operating. The division of the task organization is the FORCE. Forces are subdivided into task GROUPS, and, in turn, task groups are subdivided into task UNITS. By placing the letter of the group between the first and second numbers, the commander call may be formed. The numbers preceding the letter of the organization form the collective call. To illustrate,


let us assume that "U" designates the Atlantic Ocean. Then:

(f) To indicate numerals greater than 9 the character "X" is placed before the number to be raised and performs the operation of adding 10 to that number. For instance:



Because MTB's are relatively small craft, the problem of internal communications is far from being as complex as it is on a battleship, for example.

It is important, however, that there be efficient communications between the bridge and the engine room, the bridge and the fantail (20-mm. and depth charges) and between the bridge and the torpedo tube stations.

The principal method now used for getting word from the bridge to the various other stations on the boat is the SOUND POWER phone system. Sound power phones may be used effectively in relaying orders to the engine room, to the depth charge, or 20-mm. station. As the name of these phones indicates, they are powered by sound and not by batteries.

Another means of communication between bridge and engine room is the buzzer; There is a buzzer button in the cockpit and one in the engine room for attracting the attention of the bridge. The buzzer system is most frequently used for communicating standard orders, such as stand by to shift clutches, secure from shifting clutches, start engines, secure engines, etc. These signals should be standardized, but certain boats use variations that they have found more practicable; students therefore should familiarize themselves with the standard and special signals on boats they are on.

There are other methods of internal communications which can be used to advantage under certain circumstances. They are:

  1. Hand signals
  2. Flag signals
  3. Using a pistol shot as a signal.
  4. Installing siren for Fire or general quarters.
  5. Installing a howler on fantail for dropping charge signal.

Whatever system is used on any particular boat, it is important that student find out the systems used when on a patrol or on board for duty.


If a boat is to be able to fight effectively as a unit, its internal communications must be efficient and reliable. The man on the fantail must have no doubt as to when to drop the depth charges; so also with the men standing by the torpedoes to fire by percussion.


While the mission of the communication course is to qualify students for PT duty from a watch-standing viewpoint, it must be realized that in the short period of 2 months it will not be possible to observe all students individually in their abilities to act as radiomen.

On reporting to their respective squadrons, graduates should continue with practical instruction and above all the development of an understanding of sound communication principles.


Cartoon: Look Skipper - No Hands
Look Skipper - No Hands


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