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According to the Constitution of Japan from 1889 official name of the armed forces of Japan was “Rikukaigun”, usually translated into English as “the Army and Navy”.
There were two services in the armed forces of Japan: the Army (Rikugun, literally “Land Army”) and the Navy (Kaigun, literally “Sea Army”).
In English language terms the Imperial Japanese Army (IJA for short) and the Imperial Japanese Navy (IJN for short) become standard for each service.
According to the Constitution the supreme command of the Army and Navy was the prerogative of the Emperor (Article 11). The Emperor also determined the organization and peace standing of the Army and Navy (Article 12).
Article 12 was deliberately included in the Constitution to ensure there will be no civilian interference in military matters. Of course, there was an annual military budget, drafted by the military with the agreement with the Ministry of Finance and approved by the Diet (Parliament). But neither Diet nor other civilian body had the power to determine the number of troops, their organization, training, etc. In the 1930s a broad interpretation of this article by the military was used to silence any civilian opposition to the military control of the government.
The peculiarities of military matters were stressed by the fact, that military matters were regulated not by laws, but by “gunrei”, usually translated as military ordinances or military decrees. Ordinances were prepared by the Army or Navy ministries, signed by the respective minister and then approved by the Emperor. After that they were officially published and became equal to the laws of Japan.
There were two inter-service military bodies, which advised the Emperor in military matters.
First was the Military Council, established in 1887. It was composed of the Field-Marshals and Fleet Admirals, the Ministers of the Army and Navy, the Chiefs of the General Staff of the Army and Navy, and specially appointed Army and Navy officers. Senior-most of them become the Chairman.
Second was the Office of Field-Marshals and Fleet Admirals, created in 1898 together with the above ranks. Note, that in Japan this wasn’t a rank, but honor, awarded to the most deserving Generals/Admirals.
At the beginning of each war (including China “incident” in 1937) Emperor created another inter-service military body: the Imperial General Headquarters, usually abbreviated as IGHQ. From 1904 it comprised Army and Navy sections, led by the Chiefs of General Staffs of the Army and the Navy respectively. There was no “senior military adviser” to the Emperor like the Chairman of the Joint Chiefs of Staff in the US military – Chiefs of both General Staffs had equal standing.
Over time even the Japanese military had to admit that war is too serious a matter to entrust it to military men only. Therefore, cooperation with the Government was necessary. For many years there were informal civil-military conferences, culminating with Imperial Conferences, where most important questions were submitted for the Emperor’s approval. However, in November 1937 a permanent civilian-military coordinating body was established: the Imperial General Headquarters-Government Liaison Conference, which become the Supreme War Guidance Council in August 1944.
Both Army and Navy eventually chose the Imperial German system of military organization, where the service minister was not an unquestionable leader of the service, like he was in most other countries of the world. Instead, the minister was just the “first among equals”, who were all directly responsible to the Emperor within their areas of responsibilities.
The common Ministry of Military Affairs, existing since 1869, was divided into Army and Navy ministries in February 1872.
Initially both the Army and the Navy Ministers were unquestionable leaders of the services. But in December 1878 the General Staff (created in July 1871) became an independent body, that took over all operational control of the Army and Navy in the name of the Emperor, leaving both ministries with only administrative functions. As the General Staff was Army-dominated, the Navy obviously wanted an equal standing in the operational control of the naval forces. But only in December 1903 the Navy General Staff received an equal standing with the Army General Staff as a military command body.
Meanwhile in June 1887 Army added another top-level position, called Inspector General, renamed Inspector General of Military Training in 1898. His job was to take charge of the training of the Army and to ensure training standards are met. This position was not unusual in other armies of the world, but only in Japan it had such a high status.
The final addition of the top-level positions of the Army happened in 1938, when the position of the Inspector General of Military Aviation was created. This was the culmination of many years of the development of Army aviation, begun in 1909, when the interservice Provisional Military Balloon Study Group was created. Army Aviation Department was created in April 1919 and in 1925 expanded into the Army Aviation Headquarters, which was subordinated directly to the Army Minister. It’s worth noting that the Inspector General of Military Aviation concurrently was also the Commander of the Army Aviation Headquarters of the Army Ministry, yet such an arrangement seemed to create no serious tensions between the Inspector General of Military Aviation and the Army Minister. In April 1945 the position of the Inspector General of Military Aviation was abolished with the creation of Air General Army and only the position of Commander of the Army Aviation Headquarters remained.
The Imperial Japanese Navy had only two top-level positions, directly subordinated to the Emperor: the Navy Minister and the Chief of the Navy General Staff.
All those top-level bodies had various organizations subordinated to them. They were divided into internal and external organizations. First were integral parts of the managing body, while second were autonomous from it. For example, Weapons Bureau was an integral part of the Army Ministry, while Army Arsenals were autonomous organizations, directly subordinated to the Army Minister. This status was not set in stone. In October 1942 the very same Weapons Bureau, plus Army Technical Headquarters and Army Arsenals were integrated and reorganized into the Army Weapons Administration Headquarters – an external organization of the Army Ministry.
Besides various bodies and organizations, each service had territorial formations, to which troops were usually attached. Those were different between services.
Initially the IJA was organized into six “garrisons” in 1871, which were reorganized into 1st to 6th divisions in 1888. By 1898 there were 12 divisions, by 1915 – 20. In 1925 four divisions were disbanded (13th, 15th, 17th, 18th) to save funds for new tank, aviation and artillery units.
As the northernmost of the large Japanese Islands – Hokkaido – was too sparsely populated to establish proper garrison/division, it was decided to organize military settlers here. During 1874-1904 immigrants to Hokkaido received land and tax exemptions in exchange for their military service. As the local population grew, in 1896 it become possible to establish 7th division on this island.
Each division had its own divisional district (in peace time part of the divisional headquarters), which took care of conscription and mobilization of the division. Through subordinated regimental districts divisional district also supplied quota of the conscripts for other units in the district (cavalry, heavy artillery, fortresses, later aviation and armor, etc.), Imperial Guard divisions (first one established in 1891) and overseas “colonial” troops. Every IJA soldier was assigned to one of the regimental districts.
On mobilization, when peace time division become part of the operational forces, district formed separate headquarters, which were responsible for mobilization, forming new units, supplying reinforcements to units in the field, etc.
Besides divisions, the Kanto Martial Law Headquarters was established, when martial law was enforced in Tokyo and its surrounding areas due to the Great Kanto Earthquake in 1923. After martial law was lifted, it had to be abolished, yet it did not happen. Renamed Tokyo Security Headquarters, it become the senior headquarters in the Tokyo area, though without control of the local Guards or 1st Divisions. Besides useful political tool to control the political situation around imperial capital, this HQ become first permanent air defense HQ, becoming HQ of the Eastern Defense Command in 1935 (though thoughts control remained on the list of its responsibilities).
This air defense/thought control organization was considered good enough to spread across the whole Japan, so 1937 two more such HQs were established: Central and Western Defense Commands. Note, that Defense Commands had no authority over local troops, save for air defense.
In 1940 defense commands were reorganized into army districts: Eastern, Central, Western, plus Northern Army District was formed on Hokkaido. Unlike defense commands, army districts received direct command of all divisional districts in their area. Army district corresponded to territorial army HQ: Eastern, Central, Western, Northern Armies, which commanded all troops on the Japanese Islands.
In July 1941 General Defense Headquarters were formed to coordinate the headquarters of the Eastern Army, Central Army, Western Army, Northern Army, Korean Army and Taiwanese Army from an air defense and local defense perspectives.
Army forces in overseas possessions of Japan even in peace time were close to operational forces. Despite having local districts, they were mostly supplied with recruits from Japan. Only during the latter half of the Pacific War mobilization of the local population become norm, not exception.
Most important territorial formations of the IJN were naval bases of Yokosuka (created in Yokohama in 1871, moved to Yokosuka in 1884), Kure (created 1889), Sasebo (created 1889) and Maizuru (created 1901, in 1923-1939 Maizuru Key Port under 1st Naval District).
Naval bases tasked with all the matters of the force generation and support: maintenance of ships, supply, basic training, personnel handling, etc. Each ship or unit of the Navy was attached to one of the bases. For the purpose of managing the reservists, etc. jurisdiction of naval bases covered the whole territory of Japan and its overseas possessions, even those regions that had no access to the sea. There was an attempt to create overseas naval base in Ryojun (Chinese: Lyushun, European: Port Arthur) on the Kwantung Peninsula of China in 1906-1914, but it never achieved naval base capabilities and was “downgraded” to key port.
Naval bases were also centers of naval districts, which were responsible for protection of all the coasts of the Japanese Empire: Yokosuka – 1st, Kure – 2nd, Sasebo -3rd, Maizuru – 4th.
Independent of those two organizations were two types of naval ports: large “military ports” (existed only in the seats of the naval bases) were from 1889 supplemented by the smaller “key ports”, established in important places across Japanese Empire and newly conquered territories to supplement naval bases.
Thus
Yokosuka, for example, was at the same time place of the Headquarters of the
Yokosuka Naval Base (which at the same time was the
On November 1941 all key ports and other similar organizations were reorganized into guard districts, which officially received, besides existing port offices, some establishments and forces of the naval bases/districts (but on smaller scale).
All naval bases and guard districts were directly subordinated to the Navy General Staff in operational matters, as they were responsible for their self-defense as well as the defense of their area of responsibility. It should be noted, that guard districts were subordinated to naval bases/districts only in the administrative, not in the operational matters.
Japanese conquests of the large areas in 1941-1942 required new bases on the occupied territories, which were called “base forces”. Their responsibilities were similar to guard districts.
All operational forces were subordinated to the respective General Staff, which were exercising their command on behalf of the Emperor.
Basic building block of the IJA operational forces was the division, thought smaller formations of independent brigades, groups, regiments, battalions, units (formation between battalion and company in size), companies and sometimes even platoons also existed. Basic administrative unit was regiment, while the smallest administrative subdivision was company or independent platoon.
Despite some attempts to introduce it, there was no corps level in the IJA, so divisions and other independent units were grouped directly into armies. Armies were grouped into area armies (sometimes called fronts), which were usually the largest formations in each theater of operations. Area armies were grouped into general armies, which were equivalent of Western “army group”.
Territorial forces also had operational responsibilities for the local defense, including air defense. To coordinate these matters in 1941 headquarters of all “territorial” armies within the Japanese Empire (Japanese Islands, Korea and Taiwan) with all their troops and fortresses were subordinated to the newly-created General Defense Headquarters. It was disbanded in April 1945, when operational and territorial forces within the Japanese Empire were united for the coming “Final battle” against Allied attack on the Japanese Islands.
In peacetime, besides operational forces in the Japanese Islands, the IJA also had “colonial” forces, located in Japanese overseas possessions (besides Japanese Mandated Islands in the Central Pacific, where only a small police forces existed) and in the treaty areas in North China (along South Manchurian Railway and in Tianjin (Tientsin) area): Taiwanese Army, Korean Army, Kwantung Army, China Garrison Army. Despite small size (save for the two-divisional force in Korea), each of the forces was named “army” to ensure high status of its commander. Until 1918-1919 commanders of the Korean, Taiwanese and Kwantung Armies also served as governor-generals of the respective territories. As Japanese control over Taiwan and Korea tightened, local forces there become less colonial and more like operational forces in the Japanese Islands. Special expeditionary units were sent from Japan to reinforce those armies or in other areas of China to defend Japanese interests.
Like in other navies, basic building block and administrative unit of the IJN was warship. Unlike many navies, IJN small warships and crafts (destroyers, submarines, minesweepers, torpedo boats, etc.) were not separate administrative units, but integral parts of divisions. Another peculiarity of the IJN was, that land and air units, in other navies usually copying army/air force internal organization, were organized the same way warships were. Both warships and land/air units were administratively organized into branches by specialties, each branch having at least one division of personnel. During operations organization was different: for example, administrative chief of the aircraft carrier’s gunnery branch in combat had the position of “Close Defense Commander” (responsible for all AA defense of the ship), chiefs of the aircraft carrier’s divisions of fighter unit were the commanders of fighter squadrons, and so on. Thus, IJN administrative and operational organizations differed, while IJA administrative and operational organizations were similar.
Warships were organized into divisions, and divisions of small warships/crafts (destroyers, submarines) were organized into squadrons, that were all grouped into fleets. From 1937 there were two “area fleets” groups of several fleets (though this name officially appeared only in 1944): Combined Fleet and China Area Fleet. In 1944 with the creation of four regional area fleets under its command (another was created in 1945) Combined Fleet become an equivalent of the IJA general army, but it wasn’t officially named as such.
Like in the IJA, IJN territorial forces also had operational responsibilities for the local defense, including air defense. Surface forces of the naval and guard districts were grouped into guard forces. Just like the Army, in April 1945 operational and territorial forces were placed under the single command of the General Fleet. But unlike the IJA, this new command controlled all naval forces of the Japanese Empire both on the Japanese Islands and abroad.
Japanese Navy also had its own “colonial” forces in Central China: land units were stationed in Shanghai and Hankow, while permanent squadron was based in Shanghai (with small gunboats operating along most of the Yangtze River). If necessary, special squadrons or even fleets were dispatched to other Chinese ports, where Japanese interests were considered threatened.
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