Organization of the Imperial Japanese Army
This article details the organization of the Imperial Japanese Army.
Organization of the Imperial Japanese Army
- See article List of Armies of the Japanese Army
In the Imperial Japanese Army (IJA), the term Gun, literally meaning "army", was used in a different way to the military forces of other countries. A So-Gun, meaning "General Army", was the term used in the IJA for an army group. Of a similar but slightly lower status was a Haken Gun, or "Expeditionary Army". A Homen Gun ("Area Army" or "Theatre Army") was equivalent to the field armies of other nations and a Gun ("Army") was equivalent to a corps in other armies.
As the IJA was an infantry force the most common type of division was the infantry division. Later four tank and one parachute division were formed. The first 18 infantry divisions were originally formed as square divisions, and after 1938, most of the remainder were formed as triangular divisions with the security divisions being binary divisions. During the course of its existence the IJA organized three Guards Divisions and over 220 infantry divisions of various types (A/Reinforced, B/Standard, C/Counter-insurgency). On 7 December the IJA had two divisions serving in Japan/Korea and 50 serving abroad, most in China. During the war another 117 were raised for foreign service and 56 were raised for national defense. These totaled 223 including the Imperial Guard. Of this total no more than 35, that is one fifth of the IJA infantry division total, fought in the Pacific theatre.
The Standard, or Type "B" division was organised as:
- Headquarters (300)
- Infantry brigade (11600) 
- Three infantry regiments, each of:
- Three infantry battalions, each of:
- Escort and signal companies
- Regimental gun company, with 4 x Type 41 75 mm Mountain Guns
- Regimental anti-tank gun company, with 6 x Type 94 37 mm Anti-Tank Guns or Type 1 47 mm Anti-Tank Guns
- Field artillery regiment (2300)
- Cavalry regiment (battalion) (950)
- Headquarters and escort
- Three mounted companies
- Machine gun company, with 6 x heavy machine guns
- Engineer regiment (battalion) (900)
- Four engineer companies
- Materials company
- Transport regiment (1800)
- Up to six companies, with either carts, pack horses, or motor transport
- Divisional signals (250)
- Medical Unit (900)
- Four Field Hospitals, each of 250 personnel (1000)
- Water Purification unit (120)
- Ordnance unit (50)
- Veterinary unit (50)
It was common for a Mountain Artillery regiment, with a total of 3400 men and 36 x Type 94 75 mm Mountain Guns, to be substituted for the Field Artillery regiment, especially for operations in rough terrain. A Reconnaissance regiment, with a mix of mounted, motorized infantry and anti-tank companies, could replace the Cavalry regiment.
The Reinforced or Type "A" division generally substituted medium artillery companies with 4 x Type 91 10 cm Howitzer or long-range Type 92 10 cm Cannon for one or more field artillery companies in the field artillery regiment. It might also have an attached medium artillery battalion with three companies each of 4 x Type 96 15 cm Howitzer or long-range Type 89 15 cm Cannon, and an attached tank regiment (battalion). Conversely, the Type "C" division would lack artillery and other supporting arms.
Brigades and equivalents
The Japanese Imperial Army had two types of Mixed Brigades.
- The divisional Mixed Brigade was the semi-permanent detachment of a brigade from an Infantry Division with various Divisional support units or units attached from its Corps or Army. This provided a combined arms force of infantry, artillery, cavalry and other support units.
- The Independent Mixed Brigade was a detachment composed of various units detached from other units or independent support units formed together in a brigade. The first two Independent Mixed Brigades, formed by the Kwantung Army in the 1930s was the IJA 1st Independent Mixed Brigade and the IJA 11th Independent Mixed Brigade. Each of these brigades were organized in a unique manner and one of them, the 11th was later formed into the IJA 26th Division.
- Later a series of Independent Mixed Brigades were formed for the purpose of garrisoning the large territories of China captured in the early phase of the Second Sino-Japanese War. This variety for China was usually organized with five infantry battalions, an artillery unit, and labor troops. In the Pacific theater they had different and more varied configurations of subordinate units. Towards the end of the Burma Campaign, some were hastily formed from line-of-communication troops, and even naval personnel and conscripted Japanese civilian workers.
- The Independent Infantry Brigade; several of these were raised as garrison units, mostly for China.
- The 1st to 4th Amphibious Brigades were formed for use in the Pacific theater. These 3,500 man Sea-Landing Brigades, were used to conduct amphibious assaults on an island but afterwards they stayed to garrison that island.
The IJA maintained two types of Independent Regiments, both were used to provide garrisons in occupied areas.
- Independent Mixed Regiments: contained an infantry regiment with various support elements such as: an artillery company, engineers, supply and services, etc.
- Independent Regiments: the basic IJA infantry regiment with any attachments.
Detachments were particular military formations of the Imperial Japanese Army. Similar to German Kampfgruppen, these detachments were usually a force of infantry, artillery, armor, and other support units which were temporarily assigned for independent action and had a special mission. They were usually named after their commanders or the area in which they were to operate, and could be any size below division.
Cavalry units were formed in regiments most were either operating attached to infantry divisions or directly under a brigade attached to an army prior to the formation of the IJA Cavalry Group on 21 April 1933. There were three cavalry brigades: the IJA 1st Cavalry Brigade, IJA 3rd Cavalry Brigade, and IJA 4th Cavalry Brigade.
- Special Research Units were covert medical experiment units which conducted biological warfare research and development through human experimentation during the Second Sino-Japanese War (1937–1945) and World War II. These units responsible for some of the most notorious war crimes carried out by Japanese personnel. Initially set up as a political and ideological section of the Kempeitai military police of pre-Pacific War Japan, they were meant to counter the ideological or political influence of Japan's enemies, and to reinforce the ideology of military units
- Kempeitai Auxiliary units consisting of regional ethnic forces in occupied areas. Troops supplemented the Kempei Tai and were considered part of the organization but were forbidden by law to rise above the rank of Shocho (Sergeant Major). According to United States Army's TM-E 30-480 Handbook On Japanese Military Forces, there were over 36,000 regular members of the Kempeitai at the end of the war; this did not include the many ethnic "auxiliaries". As many foreign territories fell under the Japanese military occupation during the 1930s and the early 1940s, the Kempeitai recruited a large number of locals in those territories. Taiwanese and Koreans were used extensively as auxiliaries to police the newly occupied territories in Southeast Asia, although the Kempeitai recruited French Indochinese (especially, from among the Cao Dai religious sect), Malaysians and others. The Kempeitai may have trained Trinh Minh The, a Vietnamese nationalist and military leader. Some sources report that the Kempeitai recruited criminals as law enforcers.
- Often referred to as the "Infantry Group" in histories of World War II to avoid confusion with a Commonwealth infantry brigade, which was equivalent to a Japanese infantry regiment
- Establishment of a standard infantry division
- Scale of equipment of a standard infantry division