Naval History and Heritage Command

[Declassified] Confidential
15 January 1945

Japanese Naval Ground Forces

"Know Your Enemy!"

CinCPac-CinCPOA Bulletin 11-45

Japanese Naval Ground Forces

As the war draws closer to the main islands of JAPAN, enemy units are forced into new functions of home defense. Naval ground units, which played an important part in JAPAN's early victories, may assume an equally important role in the final attempt to deny beaches and approaches to troops invading the Empire.

An earlier survey of this subject ("Weekly Intelligence," Vol. I, No. 12) pointed out that in the period immediately following the MARIANAS campaigns the overseas use of Naval ground units by the enemy was decreasing. The offensive power of these troops, blunted in the GILBERTS and MARSHALLS, had been largely ended during the NEW GUINEA and MARIANAS campaigns. Many units had been destroyed. Disbandment and absorption of others apparently indicated that JAPAN intended to confine Naval troops outside the Empire to purely defensive garrison and service functions. The PHILIPPINES campaign may result in the isolation of most of the remaining garrisons.

In the Empire, however, the functions of Naval ground units remain important. The Navy bears the formal responsibility for the defense of harbors, Naval stations and the approaches to the Inland Sea. It seems likely, moreover, that reactivated and increased Naval ground troop units will cooperate with the Army in defensive fighting in almost any threatened locality.

The home reservoir for Naval ground replacements is large. Despite recent heavy ship losses there has apparently been no curtailment in JAPAN's Naval training programs. The number of personnel awaiting assignment in receiving barracks, training schools and other shore stations must therefore be rapidly increasing. It is logical to assume that much of this surplus Naval personnel will be used to organize and enlarge to combat strength such badly-needed organizations as [anti-aircraft] AA Defense Units, Guard Units and Special Naval Landing Forces [SNLF] (now assigned primarily defensive functions). In any case, unattached Naval personnel awaiting assignment are at least given temporary combatant organization and duties as a part of the enemy's defensive preparations. Large numbers of permanent personnel attached to the Empire's many Naval Stations will also presumably be given an emergency defense role.

Considerable new information on Naval ground units has appeared in official captured documents. This and other information is summarized in the three basic charts enclosed herewith, which are believed to present a more accurate view of the organization and disposition of Jap naval ground units than has hitherto been available.

Chart 1 shows the Naval chain of command as it relates to ground units in the Empire. This chart is based on a captured chart (CINCPAC-CINCPOA Item No. 13,069) which will be reproduced in full in a "Know Your Enemy" publication on the Japanese Air Force now under preparation.

(Comment: Following the original captured chart, Chart 1 places Guard Districts, Naval Districts, and Fleets on the same echelon as the Navy Ministry and Naval General Staff. This apparent illogicality is partly explained by the

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original chart, which indicates that a more logical working relation may be achieved through a complex parallel structure of "delegated" and "directive" authority. Since this parallel structure has no further bearing on Naval ground troop organization, it is not reproduced in Chart 1).

Chart 2 shows the chain of command of Naval ground forces outside the Empire. This chart was not taken from any single captured document, but is a logical summary of all available reliable intelligence on the subject.

Chart 3, also drawn from many sources, summarizes existing information on the actual current disposition of major Naval ground units which are now active. Locations of SNLFs, AA Defense Units and Construction Battalions are listed separately under the respective units. The disposition of major units shown on Chart 3 will shed considerable light on the probable current projected employment of Japanese Naval ground troops.

The text following is primarily an explanation of these charts. Important units will be discussed in the order of their appearance on Charts 1 and 2. Unimportant units and units not closely related to the ground troop organization will be omitted in the text.

Units in the Empire

Of the organizations on the highest Japanese Navy echelon, only Fleets, Naval Districts and Guard Districts have ground troops under their immediate command. Supporting ground troops attached to Fleets will be discussed in the section on "Units Outside the Empire."

Naval Districts

JAPAN'S four Naval Districts - YOKOSUKA, KURE, MAIZURU and SASEBO - control many functions of the utmost importance. In addition to the first-class Navy Yards located in each, Districts have charge of all recruiting, replacements, the formation of new ground units, training schools and the defense of their areas. The most important ground units attached to Naval Districts are discussed below in the order of their appearance on Chart 1.

1. Civil Engineering Departments (SHISETSUBU)

Civil Engineering Departments are responsible for the training and replacement of technicians and laborers for all Naval ground units. Construction Battalions, the primary Naval construction units, are under the command of District CE Departments during their training periods, after which they are assigned to Fleets. Construction Departments of Base Forces and Special Base Forces receive their replacements from the CE Departments through the Base Force commands.

2. Naval Barracks (KAIHEIDAN)

Naval barracks provide quarters and training for personnel awaiting assignment. The number of permanent personnel attached to each barracks is shown in

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the following table. This serves as an indication of the relative size of the barracks.

3. Guard Units (KEIBITAI)

Guard Units in the Empire are believed to serve primarily as nuclei for the defense of the areas in which they are located. They consist primarily of AA and CD [coastal defense] artillery. However, since special-weapons units, tank units and surface craft are often attached, Guard Units are capable of offensive action. They include the following departments: 1st Lieutenant, Land Defense (this department may be organized as a Special Naval Landing Force), Sea Defense, Medical, and Supply. Assigned strengths of known Guard Units attached to Naval Districts are as follows:

(Note: Guard Units may be expanded in emergency, though they do not have the extreme flexibility of Defense Units).

4. Defense Units (BOBITAI)

Defense Units are located only in the Empire. Units of this type which were formerly stationed overseas have been absorbed or redesignated as Guard Units or Base Forces.

Primary weapons of Defense Units are mines and artillery. They contain no mobile troops. However, in an emergency personnel from Naval barracks and other unattached Naval personnel might serve under Defense Units as mobile troops. Organization of a typical Defense Unit is shown in the following diagram.

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Strengths of known Defense Units attached to Districts are listed below. Since these units are capable of considerable expansion, the following figures are believed to represent nuclei only.

5. Naval Air Groups

A full discussion of ground personnel attached to Naval Air Groups for service and maintenance will appear in another special "Know Your Enemy" publication now under preparation.

Guard Districts

JAPAN's Guard Districts - located both within and outside the Empire, at OMINATO, OSAKA, CHINKAI, TAKAO, HAINAN - are similar to Naval Districts. They exist on the same echelon, and they include territory of similar extent. They do

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not, however, include Navy Yards, barracks or training schools.

1. Civil Engineer Departments (SHISETSUBU)

Civil Engineer Departments of Guard Districts are on the same echelon as CE Departments of Naval Districts. It is believed that their training functions are similar. They do not, however, appear to have the replacement responsibilities of Naval District CE Departments in the assignment of workers to overseas construction units.

2. Guard Units and Defense Units

Guard Units and Defense Units under Guard Districts are similar in function and organization to those under Naval Districts. The assigned strengths of known Guard and Defense Units under Guard District command are as follows:

3. Unattached Personnel

It is believed that unattached personnel within both Naval and Guard Districts are organized on an emergency basis as District SNLFs or Land Combat Units. A sample T/O of such an organization follows:

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Units Outside the Empire

Ground Units outside the Empire are attached to the Fleets in whose areas they operate. Areas under the command of the various Fleets are indicated in Chart 3. Fleet ground organizations are clearly separated into administrative and tactical units.

Administrative Units

Shore-based administrative organizations carry out many of the duties of Fleet administration. They are also assigned important maintenance and service responsibilities and, as necessary, limited tactical responsibilities in their areas.

1. Base Forces (KONKYOCHITAI)

Base Forces are subordinate to Fleets and are assigned to sub-areas for the administration of ground and surface units. Since these functions parallel those of Fleet commands, Base Forces are usually located in places where no Fleet Headquarters exist.

In addition to their administrative functions, Base Forces necessarily undertake limited tactical responsibilities. This is demonstrated by the Japanese Administrative Order establishing Base Forces, which states that these Forces are responsible for defense and communications in their areas and for the security of adjacent waters. In forward areas, these defense functions are obviously considerable. The same Order also states that Base Forces are responsible "when required" for "supply, construction and repair, and medical aid in behalf of the Fleet."

The organization of units composing Base Forces (see Chart 2) is obviously determined by these triple administrative, service and tactical responsibilities and is therefore subject to considerable variation. A list of strengths of known Base Forces is combined for greater convenience in use with the list of Special Base Forces which appears on page 8-9. Note that the assigned strengths of Base Forces vary considerably with their locations. Forces in forward areas, where tactical responsibilities are obviously considerable, are large. Forces in rear areas have few tactical responsibilities and are ordinarily rarely called on for Fleet maintenance functions; consequently, they are small in size. When a rear area becomes active and Fleet activities increase, units are added to the area's Base Force.

2. Fleet Service Units

Fuel Depots, Construction and Repair Departments and all other administrative and service units except Base Forces shown on Chart 2 are integral Fleet service units. These integral Fleet units perform functions identical to those performed by subordinate units of Base Forces. They are, however, separate and distinct from these units within Base Forces. Fleet service units are located at Fleet Headquarters, where no Base Forces ordinarily exist.

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An example of the relation between Base Forces and Integral Fleet units is provided by the development of the 4th Base Force (TRUK) and the 8th Base Force (RABAUL). These two Base Forces, unlike all others, were located at Fleet Headquarters. Maintenance functions which would normally have been theirs were performed largely by Fleet service units. Tactical responsibilities in these areas were also undertaken by Fleets. The two Base Forces were therefore originally small units, almost entirely administrative.

With the deterioration of the 8th Fleet and the departure of the CenPac Fleet from the TRUK Area, the two Base Forces were forced to assume larger tactical responsibilities. They also had to take over the maintenance duties formerly performed by Fleet service organizations. The former Fleet service units isolated in TRUK and RABAUL by the departure of the Fleets are, in fact, believed to have been incorporated into the Base Force organizations. In this way, both Forces probably became capable of performing all the normal functions of Base Forces.

Tactical Units

1. Special Base Forces (TOKUBETSU KONKYOCHITAI)

Special Base Forces are assigned to Guard Districts and Fleets for employment. It is not known which Special Base Forces are assigned to Guard Districts.

Special Base Forces have considerable similarity to Base Forces in function. They are, however, primarily tactical rather than administrative organizations.

This difference is demonstrated by the locations and assigned strengths of Special Base Forces, indicated on the list which follows. Special Base Forces are ordinarily located either at Fleet Headquarters or in forward areas. The Special Base Forces located in rear areas are obviously mere nuclei, capable of expansion in emergency. Those located in forward areas bear considerable combatant responsibility and often have Guard Units, SNLFs and other combatant units under their command. Special Base Forces located at Fleet Commands share their service, maintenance and administrative functions with integral Fleet units. Special Base Forces are therefore assigned "partial responsibility" for their various defense and maintenance functions by the order establishing them, whereas Base Forces are assigned full responsibility for similar functions.

The difference between Base Forces and Special Base Forces is further demonstrated by the fact that the 5th Special Base Force (SAIPAN) and the 30th Special Base Force (PALAU) were changed to Base Forces when Admiral NAGUMO's CenPac Area Fleet Headquarters was moved to SAIPAN. Since this Fleet Headquarters was temporary, it did not have the integral service and administrative units which ordinarily make a Base Force unnecessary at Fleet Headquarters. The new Base Forces were enlarged to provide for the Fleet's administrative and service needs. According to a POW captured on SAIPAN, an additional reason for the change was that Admiral NAGUMO, again departing from usual practice, wanted no separate tactical commands in his new Fleet Area. This objective also was achieved by changing the two units from Special Base Forces (tactical) to Base Forces (largely administrative).

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Special Base Forces, probably because of their tactical responsibilities in forward areas, have more definite T/Os than Base Forces and are not subject to such drastic changes in size. The typical organization of a Special Base Force is indicated on Chart 2.

Base Forces and Special Base Forces identified since the beginning of hostilities are listed below with their organizational strength. (Comment: An asterisk after a strength indicates that it was obtained from unofficial documents).

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2. Guard Units (KEIBITAI)

Composition and function of Guard Units have already been described under Empire-based units. Guard Units outside the Empire are ordinarily assigned by Fleets to Base Forces and Special Base Forces. They are in turn assigned by these commands to take charge of the land and sea defense of particular localities.

Guard Units, within their localities, take full charge of the distribution of troops and weapons, maintenance of lookout and communications, and patrol of nearby waters. Air units within the territory of Guard Units are independent of the Guard Unit command, but the Guard Unit is responsible for the defense of airfields.

Guard Units are frequently assigned semi-civil responsibilities such as the internment of foreigners, the policing of natives, etc. within their jurisdictions.

Locations and assigned strengths of known Guard Units outside the Empire are listed below. Note that these units, like most Naval ground units, are subject to considerable variation in size according to the current importance of activity in their areas and the presence or absence of other military units. (Comment: Strengths marked with an asterisk were obtained from unofficial captured documents).

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3. Special Naval Landing Forces (TOKUBETSU RIKUSENTAI)

SNLFs, like some other Naval ground units, have varied greatly with the course of the war. In the early months of the war, their mission was primarily one of assault. It has since become almost entirely defensive. Consequently, SNLFs, formerly consisting principally of infantry, have become chiefly heavy-weapons units.

Many SNLFs have been destroyed or so shattered that the remnants have been absorbed by units of other types. In several instances two or more SNLFs have been combined for particularly important missions.

A sample T/O of a well-balanced combined SNLF, equipped for primarily defensive duties, appears on the opposite [following] page. (This chart was originally published by CICSOPAC in March, 1944). Although this particular unit (the 8th Combined SNLF) no longer exists, the organization outlined is believed representative of the fairly recent development of SNLFs.

SNLFs identified since the beginning of hostilities are listed below. (Comment: "WD" indicates that data was derived from confidential Order of Battle publications issued by the War Department).

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4. AA Defense Units (BOKUTAI)

Naval AA Defense Units are independent units assigned by Fleets to Base Forces, Special Base Forces, Guard Units and SNLFs, according to tactical needs. As indicated in the charts on pages 16 and 17, AA Units are of three types. Type A includes AA artillery and machine-guns, Type B machine-guns only, and Type C machine-guns and machine-cannon.

Locations of AA Defense Units identified since the beginning of hostilities are listed below.

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5. Shipboard AA Defense Units (SEMPAKU BOKUTAI)

Shipboard AA Defense Units differ in organization from all three types of shore-based Defense Units. Normally, shipboard units do not exceed 124 men. Such organizations are believed to be assigned to convoys as needed and divided among the several ships.

Distribution of known Shipboard AA Defense Units is indicated by the following list.

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6. Construction Battalions (SETSUEITAI)

Construction Battalions are highly mobile independent units, fully equipped for major construction tasks. Following their training period under the Civil Engineering Departments of Naval Districts, they are assigned to Fleets. Fleets assign them in turn to Base Forces, Special Base Forces and Guard Units for work on particular projects, such as airfields and field fortifications.

Construction Battalions are made up of skilled workers, supervised by civil engineers and Naval officers. They are internally organized according to the laborers' special skills. A sample organization is demonstrated by the diagram reproduced on page 20.

Construction Battalions maintain a close liaison with other Naval construction units. When Battalions are located at Fleet Headquarters, they receive supplies and supervision from Fleet Civil Engineering Departments, which are one type of the integral Fleet service units discussed above. When Battalions are located in Base Force Sub-Areas, these functions of supervision and supply are performed by Base Force Construction Departments (KENSETSUBU), which are subordinate units of Base Forces.

Locations of Construction Battalions identified since the beginning of the war are listed below. (Comment: "WD" indicates that data was derived from confidential Order of Battle publications issued by the War Department).

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