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"Japanese Signal Services" from Tactical and Technical Trends

The following U.S. intelligence report on Japanese signal services during WWII was originally published in Tactical and Technical Trends, No. 46, May 1, 1944.

[DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]


Before the war the functions of the Signal Corps were performed by communication units of the Corps of Engineers. In 1941, however, a Signal Corps was established under the Inspectorate of Communications, directly subordinate to the war department general staff which seems tantamount to the establishment of a separate Signal Corps. The Corps consists of at least two signal replacement regiments, a number of signal (telegraph) regiments, line of communication signal units, shipping signal units, air signal units and division, regiment, and battalion signal companies or sections.

a. General

The signal regiment (army signal unit) is reported to be composed of a headquarters, several wire companies, either motor, draft, or pack, several radio platoons, motor, draft or pack, a fixed radio unit, a radio intercept unit and a field pigeon unit.

The headquarters consists of about 120 officers and men and includes a transport section, a repair section, and an air-ground radio section.

The wire company approximate strength is: 260 men (draft), or 320 (pack), or 300 (motor). They are each equipped with 36 telephone instruments and 8 telegraph instruments. The draft and pack companies carry about 35 miles of wire and the motor companies 70 miles of wire. All companies are thought to include a signal platoon, 3 maintenance platoons and a transport platoon.

Radio platoons operate one radio station. They include either draft, pack or motor transportation and are from 35 to 45 men in strength.

The fixed radio unit has a strength of about 25 officers and men and operates a long distance radio station.

The radio intercept unit is divided into a headquarters with supply train, an intercept unit equipped with six receivers, and a direction-finder unit equipped with 4 direction finders. Strength approximately 290 officers and men.

The line of communication signal unit is composed of a headquarters including a train and a radio section (114 officers and men), several line of communication signal companies (384 officers and men, 3 maintenance and 1 operating platoon, 46 telephones, 2 telegraph instruments, about 100 kilometers of wire). There is also a line of communication reserve signal company (159 officers and men) which is probably charged with major maintenance duties,

Shipping signal units are composed of headquarters and two companies. Personnel is assigned to maintain radio liaison between transports and shipping establishments. Companies have strength of about 300 while the regiment totals 635 officers and men.

The air signal unit is a company of about 320 officers and men. It is divided into three platoons and is employed mainly in maintaining communications within the air brigade. The unit probably also operates direction-finder apparatus.

Independent telephone and radio units are assigned as needed. In lower echelons such as divisions, allocations of communication personnel and equipment depend entirely on the tactical situation, similar to the practice in the German army. In the case of the latter, the storage and issue of signal equipment (except food and clothing) is a function of the Ordnance.

Communication personnel or "signalmen" as they are known in all units from division down belong to separate units, usually platoons. These platoons are trained principally by several permanent regiments in Japan and one or more in occupied China.

So-called signal replacement regiments act as administrative main depots and training centers for all communication personnel. These regiments do not move overseas--but are used constantly as centers for training such signal units as telephone and radio platoons, telephone and radio sections and special headquarters units. These platoons, companies and special units are then assembled as required and are used to form units of varying size and tactical application from small companies up to army. Each sub-unit, however, retains its identity and can be detached as required.

b. System of Recruitment

Originally, communication personnel upwards of division headquarters were supplied from "Engineer Communication Regiments" whose signalmen had volunteered to take up signal work. They remained engineer personnel, as the regiments were engineer units. These units are now considered as signal regiments. Presumably this system of recruiting signalmen could not meet the demands of the army when Japan entered the war and, as a consequence, two additional sources of supply were evolved as follows:

Recruits and/or reservists called back into service were assigned to an army communication unit or sub-unit in Japan or a quiet station in occupied China. After some basic training they were sent to army signal schools, or communication regiments where they received specialized radio and telephone instructions. After completing this training, they were assigned to an army communication unit or sub-unit.

Those between 15 and 18 years were recruited and sent to an army signal school for a training period of two years; subsequently, they were assigned to army communication units as required.

Communications from below division headquarters formerly were maintained by signal units whose personnel were originally drawn from the division and trained locally. There is every reason to believe that this system has been abandoned in favor of the system referred to above, with the exception that recruits are assigned direct to division or regimental signal units, and from there to army signal schools or communication regiments for higher training.

c. Chain of Communications

[Japanese Chain of Communications - WWII]

d. Army Signal Units

Army communication units are responsible for communication between army headquarters and lower commands. They consist of headquarters commanded by a colonel, who is Chief Signal Officer for the army, and an army communication company which is responsible for the signal lay-out and communications at army headquarters. The rest of the army communication units are made up of a number of wire and radio units to suit the current operation, and thus complete flexibility is achieved.

Although the main role of the army communication unit is to establish, operate., and maintain communication between army headquarters and division headquarters and to serve miscellaneous sections between those units, it is quite normal for units to be detached from army signal personnel and allotted to divisions. These units in turn may supplement existing communications by sub-allotting sub-units even down to battalions.

The organization and equipment of these units varies according to their different roles. For example, an independent radio company which is usually allotted to a division, consists of two platoons sub-divided into approximately eight sections each, and equipped with Model 94 Type 3 A, Model TM Type 2, Model 94 Type 5, and/or Model 94 Type 2 B radio sets. The Model 94 Type 2 B is also used in the division signal units. A fixed radio company is a comparatively static unit, equipped with long-range Model 94 Type 1 Transmitter Modification No. 1 or Model 95 sets for communicating between the army headquarters and GHQ.

e. Division Signal Units

The division signal unit takes over where the army communication unit leaves off. This is commanded by a major or captain and contains approximately 250 officers and enlisted men.

The organization chart shown is considered to be accurate; it must be regarded, however, as a basic TO only. Although certain division organizations are known to correspond with the diagram, the Japanese modify the division signal unit to suit the operation at hand. It is interesting to note, however, that the radio platoon is seldom altered, the modifications usually taking place in connection with the wire platoons.

[Division Signal Unit]

The division signal unit is responsible for communications between division headquarters and regimental headquarters and also between division headquarters and division troops. The unit works very closely with the regimental signal companies, and issues extra equipment such as telephones, wire, etc., to them. It also functions as a depot for the signal companies. It is considered improbable that the unit allots sections lower than regimental headquarters except under very special circumstances, because it has insufficient equipment.

The officers and NCOs in the unit are armed with pistols, enlisted men with Type "38" rifles. The signal equipment includes the type "92" telephone, insulated cable, insulators, poles and tools. The ground radio set is Model 94 Type SP 3 A, but the type of ground-air radio telephone set is not known.

f. Infantry Regimental Signal Company

The regimental signal company provides communications down to communication sections in the infantry battalion. The Japanese have no signal battalions per se, but communication sections are attached to infantry battalions. Within the battalion, however, liaison NCO's and messengers form part of each Hq down to and including platoons. There does not seem to be any standard allotment of telephones or radio sets for battalions.

Each battalion Hq has a line and telephone to regimental Hq, and when this is not possible, a radio section is allotted. The issue to the rest of the battalion varies from 0 to 6 telephones or 0 to 4 Model 94 Type 2 B radio sets, or 0 to 3 Model 94 Type 5 radio sets, all according to the tactical situation. Cases have occurred in the South Pacific where even sections on combat outpost duty, have had both a telephone and radio available; furthermore, platoons on patrol in Arakan have included a signal detachment with a Model 94 Type 5 radio set.

Although the regimental signal company is a more conventional organization than other Japanese signal units, this too is liable to be altered as required tactically. It is possible, however, that the alterations are made by exchanges with one or both of the other regimental signal companies in the division. One infantry regimental company in Burma had four wire sections in No. 1 platoon, instead of the more normal, two wire and two radio sections, The reasons for this are not known but may have been due to shortage of radio equipment or its pooling within the division for special operations.

The company is commanded by a captain or lieutenant and has a total strength of 132. Like the division signal unit, the officers and NCO's are equipped with pistols and the enlisted personnel with type "38" rifles. The heavier equip- ment is normally carried by pack transport, but motorized vehicles and even bicycle trailers may be made available. A certain amount of the lighter equipment is probably carried by enlisted personnel during active operations. The Model 94 Types 5 and 2 B sets are both man-pack size and weight.

The regimental signal company comprises 4 officers and 128 men divided into a headquarters (1 officer and 29 men), a radio platoon (1 officer and 72 men), and a wire platoon (2 officers and 28 men).

The radio platoon is divided into 8 sections of about 9 men each. The first six sections operate Model 94 Types 5 or 2 B radios with ranges up to about 15 miles. The seventh and eighth sections each operate a portable radio for air-ground liaison.

The wire platoon is divided into 4 or 5 sections of about 7 men each. Each section operates three field telephones.

The signal company is equipped with 3 switchboards and 20 miles of wire on six reels. The equipment is packed on either 40 pack horses, 19 two-wheeled carts or 14 trucks. Armament usually includes about 45 rifles, and each man is provided with a bayonet and 3 hand grenades. Personnel are trained in visual signalling as well as in the use of panels and pick-ups for air-ground liaison. Frequently dog sections and pigeon sections are attached. The company detaches units to operate with subordinate organizations of the regiment as they are needed.

g. Methods of Communication

The principal methods of communication between Japanese units are by telephone and radio, it is the guiding principle, however, that where possible, wire is to be used. It is presumed that this order was initiated for reasons of security -- since there is nothing to suggest weakness in the Japanese radio organization. It also frees radio for use of mechanized elements and air-ground liaison.

Even in the use of wire communications, captured orders indicate that only commanders and their representatives are permitted the use of voice telephone, and that others are required to submit written messages to the operator for transmission by the buzzer phone incorporated in the type "92" telephone.

The Japanese alphabet (also called syllabary) consists of about 50 characters, as compared with our alphabet of 26 letters. The Japanese are therefore unable to use the international Morse code and have invented a "Morse" of their own, running into 5 dots and dashes for each individual letter, as the case may be (see Tactical and Technical Trends, No. 12, p 45 for further reference to examples of phonetic Japanese used in communication).

For the same reason they cannot use the semaphore system where signalling with two flags is done, and so a code of numbers representing the 50 characters is used, for example: A = 00, I = 01, U = 02 and so on. The system also lends itself to simple prearranged code signals, such as:
               76 . . . . . . . "Have completed preparations"
               83 . . . . . . . "Indicate battle line"

(1) Telephone

Telephone line units are equipped with insulated cable, yellow, assault and field wire similar to W-130 and W-110B except single conductor telephones (mainly Type "92" telephone and buzzer telegraph combined), bare copper wire, poles, insulators, tools, etc. Ground return party lines rather than switchboards seem to be the rule in jungle operations. The use of "insulated cable" was not noted at Guadalcanal, but its use elsewhere may have been reported. The Australian field wire apparently has been mistaken for Japanese "insulated cable" in some reports.

Wire men are trained in the use of the field telephone, telegraph, wire-laying and repairs. There is one instance reported where a prisoner stated that he had been trained to lay a 500-meter reel of wire across flat country in 3 to 5 minutes!

(2) Radio

When wire is impracticable, radio is used extensively; this applies particularly in very mobile operations, when tanks, artillery and infantry may be linked so as to be able to communicate with each other.

In considering the island-to-island operations in the SW Pacific area, it should be pointed out that the Japanese are using high-powered radio installations for communication from island to island. The sets used are both high and low frequency. Moreover, a general trend has been seen that indicates the Japanese are using radio in smaller units much more at the present time than in the past.

The statements which follow are predicated on equipment which was captured in the northern Pacific, South Pacific and Southwest Pacific areas. In these places the Japanese have been engaged in holding operations. Being on the defensive, they have not used their latest and most modern equipment. In the Burma area where the Japanese have been on the offensive, it may be expected that their most modern equipment will be encountered.

The Japanese lay most emphasis for communication, on wire. The wire is laid as soon as possible by their forward elements. However, radio is used first where communications must be established rapidly. After their wire communications have been established, radio assumes a secondary role as a stand-by communication link. On one island installation a local radio link had been established using a 100-watt short wave transmitter at the headquarters plant.

h. Radio Equipment

The apparatus captured so far shows obsolescent design. The circuits and components used are comparable to those that were in use in the Allied Nations around 1935 to 1937. Almost invariably the transmitters and receivers use plug-in coils to cover the various bands. The transmitters of power, up to 50 watts, use simple Hartley oscillator circuits connected directly to the antenna. The smaller receivers use regenerative detectors without radio frequency amplification. While arrangements such as this are simple to service and maintain, the frequency stability suffers greatly. It would be very difficult to "net" these radio sets and keep them on frequency.

A great variety of small transceivers and transmitter-receiver combinations of one to two watts power are in use. These sets are usually man-pack. The transceivers are contained in one case, carried on the chest, while the batteries are in another case carried on the back. In the case of the small transmitter- receiver sets, the transmitter, receiver and batteries, and the hand generator for transmitter power, are all carried in separate cases, making it necessary to use from two to three men to pack and operate a set. Sets of from 10 to 50 watt power are usually of the portable type, the total apparatus being carried in 4 or 5 separate cases, and power connections being made by plugs and cables. The sets in general have a complexity of controls that does not lend itself to ease of operation. As an example, the Japanese Direction Finder and Intercept Receiver, Model 94, Type 1, has so many controls that a comparatively long period of time must be taken to get an accurate "fix" on a transmitter.

While these disadvantages have been noted, it must be borne in mind that the Japanese operators have been well-trained and are capable of making good use of their equipment.

All radio transmitters so far examined except "walkie-talkies" had one crystal furnished in addition to master oscillator. A bank of about 35 spare crystals of different frequencies was found at one regimental signal unit bivouac. These crystals are reported to be of excellent quality.

The wide frequency range of the Japanese radio transmitters makes them capable of utilizing the frequencies most effective for sky-wave transmission at any given time.

Many ammeters both for antenna and power are supplied with separate shunts so that the same meter movement can be used with many different equipments.

In spite of the fact that Japanese signal equipment is designed for maximum portability and that use in the jungle and for amphibious operations was to be expected, no attempt was made to make these sets moisture or fungus-proof. Poor grade insulating materials were used which are subject to failure under jungle conditions. To offset this deficiency, operators give their equipment excellent care, keeping it as free as possible from dirt and corrosion.

A multiplicity of types of radio tubes is used, complicating the supply problem. Receiving tubes are often microphonic, due to faulty construction. The supply of dry batteries is facilitated by the restriction to a very few types, avoiding special types for each type of equipment. Battery boxes are adapted to accommodate standard types.

One of the most noteworthy features of Japanese radio installations is the excellent camouflage and concealment used. Locations are carefully selected, and fullest advantage is taken of natural cover. Large antennas are arranged with ropes and pulleys to permit raising to the tops of trees for maximum efficiency or to be lowered when necessary for concealment or adjustment.

There is no evidence of frequency modulated equipment. All phone transmitters examined to date are amplitude modulated.

(1) Airborne Radios

The Japanese airborne transmitters and receivers are sturdily built and compactly constructed with excellent workmanship and material. More thought appears to be given to compactness of design than to ease of maintenance. To some extent, their equipment is designed to fit a particular space on each aircraft rather than standardizing on a general type for all aircraft. It has been noted that some of the Japanese tubes were equipped with leather handles to facilitate removing. Japanese equipment uses a large amount of aluminum, so that even bulky pieces of equipment are unusually light in weight. No precautions have been taken against corrosion and for fungus control. Reports indicate that Japanese types of equipment manufactured since 1940, are far superior to their older models.

Electrically and mechanically this new radio equipment appears equal to the Allied Nations standards.

It has been noted that all Japanese planes do not have radio equipment, the leader of a flight probably being equipped. This, it is believed, is for purposes of security. While radio direction finders are standard equipment on medium and heavy bombers, there have been no reports indicating that they are normally fitted to fighters.

Radio equipment that was made in America, either in whole or in part, has been found on several Jap Zero fighters (Zekes). While components of German and English manufacture have been noted, most of the component parts are of Japanese manufacture. The exact imitation of American or German design has been noticed in their equipment. There is no evidence of quantity production, as all equipment noted is hand-made and of good construction. Crystals of very good quality are used in the majority of Japanese airborne radios to control the frequencies of both the transmitters and receivers. The Japanese apparently have no standard of design or finish. In many instances, the equipment is so compactly constructed that it is difficult or even impossible to service.

(2) Ground Radio Sets

The radio sets used in the division set-up range from the powerful 1,000-watt fixed station set to the small one man pack radio telephone sets (similar to SCR-194) set which is used by forward units.

(a) Model 94 Set (Third Series Unit "A")

Model 94, third series, Unit "A" may be the set described as follows: two-watt set, frequency range 2,000 to 2,500 kc and 4,000 to 5,000 kc. One set examined consisted of two separate boxes for transmitter and receiver, and a small hand generator for the transmitter. The receiver had self-contained battery supply. Both CW and voice are provided. It was found to be the most common set and was distributed down to infantry battalions. The transmitter was a twin triode tube with Heising modulation.

Its range is about 12.5 miles on CW and it is packed in two boxes carried by one pack animal or by two men. This radio is also distributed to cavalry and field artillery units from the brigade down to battalion.

(b) Model 94 (Type 5 Model 32)

This is a 4-tube set with a small hand generator for transmitter and batteries for receiver. Frequency range transmitter 779 to 3,061 kc and frequency range receiver 779 to 7,000 kc. It is a receiving and sending set and the latter range is 3.7 miles. It is used for communication between the artillery battalion, regimental and brigade headquarters; and with infantry regimental and brigade headquarters.

(c) Model 94, (Second Series, Unit "B")

This is a 200-watt transmitter, using 1,300 volts for plate from a gasoline driven generator similar to our PE-49. The transmitter uses a "UV814" tetrod and a "UV49C" pentode. Frequency range: 950-6,675 kc. The receiver is a super-heterodyne, frequency 140-15,000 kc with 7 plug-in coils. Two IF frequencies are used, 100 or 400 kc. It is used for air-ground communication, and is known as No. 6 radio set to the operators.

(d) Model 87 Radio Set Type 2

This is an air-ground set. The ground transmitter set is said to contain four tubes and to be used for either code or telephone. Range with the telephone varies considerably with a maximum of 190 miles under ideal conditions. The airplane transmitting and receiving set is contained in a box 10 x 18 inches by 8 inches deep, and is said to receive voice communication to the full range of the ground set.

(e) NA 3 Airborne Set

This is a twenty-watt short-wave radio telegraph set used as a ground set with a total weight of 30.2 pounds and an effective distance of 1,240 miles under ideal conditions.

Transmitting equipment data is as follows:

           20 watts . . . . . . . CW telegraph
           15 watts . . . . . . . Tone telegraph
           Frequency: 5,000 kc on CW telegraph and tone telegraph,
                      6,590 kc crystal controlled

Keying on continuous wave (CW) telegraph is obtained by positive keying in the radio frequency amplifier circuits. Tone telegraph is obtained by grid modulation. A maximum of 20-watts output may be obtained over short periods of time after a forced landing.

Receiving equipment consists of 4 tubes with a frequency of 2,000 to 20,000 kc and 300 to 2,500 kc. The engine has ignition shielding to eliminate interference.

The source of power - receiving and sending - primary, 24 volts, 15 amperes; secondary, 700 volts, 150 milliamperes. Low voltage is connected to the lighting circuit. The storage battery is 24 volts, 15 amperes. It is charged by a generator connected direct to the motor and equipped with voltage stabilizer. Twenty-five volts, 14 amperes at 2,800 to 4,800 revolutions per minute.

The antenna is in the form of a fixed, inverted L, 22.9 feet long and grounded to the fuselage. Because of the air resistance caused by windmill generators, the generator is often coupled directly to the motor.

(f) Large Ground Set

This cannot be identified by nomenclature. A 1-kilowatt transmitter powered by 2,500 volt generator driven by diesel engine was captured on Guadalcanal. Operating position included two field desks, each incorporating several receivers Model 94. This was at a division or higher headquarters. Transmitter was installed in the open, covered with tarpaulin and palm fronds. Power supply was located in a hut of palm fronds -- the operating position in a dug-out.

i. Telegraph Sets

"Type 95" was used at division headquarters to higher headquarters. It was of elaborate construction, battery-operated, incorporating both howler and sounder, with small loud speaker.

j. Visual

This method of intercommunication is divided into two parts: (a) normal visual telegraph, semaphore, lamp, etc; and (b) signals with a prearranged meaning using ground panels, flags, pyrotechnics, etc.

Although the Japanese consider visual methods a poor means of inter-communication, they realize that occasions may arise during active operations when the only possible way of communicating a message is by visual signalling. Therefore, the use of flags, lamp and heliograph are taught at signal schools.

Small flashlights with filters of three colors are issued to front-line units. These are apparently used primarily for identification purposes, rather than for blinker signalling, as the keying arrangement is poor. Signal lamps of good construction similar to our EE-84 were found in the hands of Japanese units in Guadalcanal, but these lamps were not observed in use.

Visual equipment for use by division and regimental signal units is in a regimental pool and carried with the spare arms and equipment.

In contrast to their dislike of visual signalling, the Japanese use pre-arranged signals extensively, and have evolved some very ingenious methods for this type of signalling. Examples include: indicating targets to mortars and artillery with tracer fired from medium machine guns, colored smoke, parachute flares fired from mortars and grenade dischargers, "trail-blazing" and special markers. In one division, battalions have "commanding officer's flags" down to and including platoons for giving prearranged signals on the move.

k. Personnel

NCOs and men are employed extensively for intercommunication in small units. They may be: -

(1) Liaison NCOs--sergeants and corporals are appointed for liaison duties down to platoons and it is probable that they pass orders verbally to lower units and report to their Hq on the situation, as and when necessary.

(2) Couriers--Motorcycle combinations are used for liaison duties, but no separate establishment exists for couriers in signal units.

(3) Orderlies--Mounted orderlies may be drawn from cavalry units as required.

(4) Runners and bicyclists are widely employed.

l. Animals

Pigeons--Most signal units have used pigeons and certain division signal units are known to have pigeon sections consisting of 1 NCO and 8 men. The number of birds in the section, however, is not known. The birds have been used up to a range of 70 miles, and averaged 40 mph.

Messenger Dogs--As yet no messenger dog units have been identified, but a large messenger dog training depot is-known to have been in existence at the Infantry School prior to Japan's entry in the war. The dogs were trained in carrying messages, as well as in non-communication duties.


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