Imperial Japanese Navy Air Service

The Imperial Japanese Navy Air Service (大日本帝國海軍航空隊) was the air arm of the Imperial Japanese Navy during World War II. The organization was responsible for the operation of naval aircraft and the conduct of aerial warfare in the Pacific War.

It was controlled by the Navy Staff of the Imperial Japanese Navy and the Navy Ministry. The Imperial Japanese Navy Air Service was equal in function to the Royal Navy's Fleet Air Arm (FAA), the U.S. Navy's Naval Aviation branch, the Italian Navy's Aviazione Ausiliara per la Marina, or the Soviet Navy's Morskaya Aviatsiya.

The Imperial Japanese Navy Aviation Bureau (Kaigun Kōkū Hombu) of the Ministry of the Navy of Japan was responsible for the development and training.

The Japanese military acquired their first aircraft in 1910 and followed the development of air combat during World War I with great interest. They initially procured European aircraft but quickly built their own and launched themselves onto an ambitious aircraft carrier building program. They launched the world's first purpose-built aircraft carrier, Hōshō, in 1922. Afterwards they embarked on a conversion program of several excess battlecruisers and battleships into aircraft carriers. The IJN Air Service had the mission of national air defence, deep strike, naval warfare, and so forth. It retained this mission to the end.

The Japanese pilot training program was very selective and rigorous, producing a high-quality and long-serving pilot corps, who ruled the air in the Pacific during early World War II. However, the long duration of the training program, combined with a shortage of gasoline for training, did not allow the Navy to rapidly provide qualified replacements in sufficient numbers. Moreover, the Japanese, unlike the U.S. or Britain, proved incapable of altering the program to speed up training of the recruits they got. The resultant decrease in quantity and quality, among other factors, resulted in increasing casualties toward the end of the war.

Japanese navy aviators, like their Army counterparts, preferred manueuverable aircraft, leading to lightly built but extraordinarily agile types, most famously the A6M Zero, which achieved its feats by sacrificing armor and self-sealing fuel tanks.

Origins
In 1912, the Royal Navy had informally established its own flying branch, the Royal Naval Air Service. The Japanese admirals, whose own Navy had been modeled on the Royal Navy and whom they admired, themselves proposed their own Naval Air Service. The Japanese Navy had also observed technical developments in other countries and saw that the airplane had potential. The following year, in 1913 a Navy transport ship, the Wakamiya was converted into a seaplane tender, a number of aircraft were also purchased.

Siege of Tsingtao
On 23 August 1914, as a result of its treaty with Great Britain, Japan declared war on Germany. The Japanese, together with a token British force, then laid siege to the German held territory of Kiaochow and its administrative capital Tsingtao on the Shandong peninsula. During the siege, starting from September, Maurice Farman seaplanes onboard (two active and two reserve) the Wakamiya conducted reconnaissance and aerial bombardments on German positions and ships. On 30 September the Wakamiya was later damaged by a mine, but the seaplanes (by transferring to land) continued to used against the German defenders until their surrender on 7 November 1914. The Wakamiya conducted the world's first naval-launched aerial raids in history and was in effect the first aircraft carrier of the Imperial Japanese Navy. By the end of the siege the aircraft had conducted 50 sorties and dropped 200 bombs, although damages to German defenses were light.

Interwar Years
The Japanese navy had closely monitored the progress of aviation of the three Allied naval powers during World War I and concluded that Britain had made the greatest advances in naval aviation

The Sempill Mission was a British aeronaval technical mission led by Captain Sempill and sent to Japan in September 1921, with the objective of helping the Imperial Japanese Navy develop its aeronaval forces. The mission consisted in a group of 29 British instructors, headed by Captain William Sempill, and stayed in Japan for 18 months. The British government hoped it would lead to lucrative an arms deal. The Japanese, were trained on several British aircraft, such as the Gloster Sparrowhawk, in various techniques such as torpedo bombing, flight control and carrier landing and take-offs. Skills that would later be employed in the shallow waters of Pearl Harbour in December 1941. The mission also brought the plans of the most recent British aircraft carriers, such as the HMS Argus and the HMS Hermes, which influenced the final stages of the development of the carrier Hōshō. The Hōshō became the first designed aircraft carrier from the keel up to be built. The military in Japan were also aided in their quest to build up their naval forces by Sempill who had become a Japanese spy. Over the next 20 years, the British Peer provided the Japanese with secret information on the latest British aviation technology. His espionage work helped the Japanese rapidly develop its military aircraft and its technologies before the Second World War.

Under the Washington Naval Treaty two incomplete battlecruisers were allowed to be rebuilt as carriers, for the Japanese; the Akagi and the Amagi. However the Amagi was damaged during an earthquake in 1923 and the Kaga became a replacement. With these two carriers much of Imperial Japanese Navy's doctrines and operating procedures were established.

IJNAS vs US first encounter (1932)

 * During the Shanghai Incident on February 22, 1932 Lt Robert Short (US Army Reserve) while piloting a Boeing 218 with Chinese markings damaged one IJN Type 13 carrier attack aircraft, killing the pilot, Lt. Kotani and wounding the observer, before he was killed in action. Reportedly three days previously Short had shot down IJN Lt. Kidokoro.

Sino-Japanese War
From the onset of hostilities in 1937 until forces were diverted to combat the Americans in 1941, the Imperial Japanese Navy Air Service played a key role in military operations on the Chinese mainland. Despite the fierce rivalry between military branches, in the fall of 1937 General Matsui Iwane, the Army general in command of the theater, admitted the superiority of the Naval Air Services. His combat troops relied on the Navy for air support.

Aircraft attacked Chinese positions in Shanghai and surrounding areas, naval bombers such as the G3M and G4M were used to bomb Chinese cities. Japanese fighter planes, notably the Mitsubishi Zero, gained tactical air superiority; control of the skies over China belonged to the Japanese. Unlike other naval airforces, the IJNAS was responsible strategic bombing and operated long ranged bombers.

The Japanese strategic bombing were mostly done against Chinese big cities, such as Shanghai, Wuhan and Chonging, with around 5,000 raids from February 1938 to August 1943.

The bombing of Nanjing and Guangzhou, which began on 22 and 23 September 1937, called forth widespread protests culminating in a resolution by the Far Eastern Advisory Committee of the League of Nations. Lord Cranborne, the British Under-Secretary of State For Foreign Affairs, expressed his indignation in his own declaration. Words cannot express the feelings of profound horror with which the news of these raids had been received by the whole civilized world. They are often directed against places far from the actual area of hostilities. The military objective, where it exists, seems to take a completely second place. The main object seems to be to inspire terror by the indiscriminate slaughter of civilians...»

World War II
At the beginning of the Pacific war the Navy Air Service consisted of five naval air fleets In April, 1941 the First Air Fleet was created, concentrating the Navy's carriers into a single powerful striking unit The Japanese had a total of ten aircraft carriers: six fleet carriers, three smaller carriers, and one training carrier. The 11th Air Fleet contained most of the Navy's land based strike aircraft.

On December 7, 1941, the Imperial Japanese Navy attacked Pearl Harbor crippling the U.S Pacific Fleet and destroying over 188 aircraft for a loss of 29 aircraft. On December 10, land based bombers of the 11th Airfleet were also able to sink HMS Prince of Wales and HMS Repulse.

There were also air raids on the Philippines and on attacks Darwin in northern Australia.

From 16 December 1941 to 20 March 1945 IJN aviation casualites killed were 14,242 aircrew and 1,579 officers.

Aircraft strength 1941
The IJNAS had over 3,089 aircraft in 1941 and 370 trainers.
 * 1,830 first line aircraft including:
 * 660 fighters, 350 Mitsubishi Zeros
 * 330 Carrier based strike aircraft
 * 240 land based twin engined bombers
 * 520 seaplanes (includes fighters and reconnaissance) and flying boats.

World War II Aircraft
Fighters:
 * Mitsubishi A5M (Type 96 carrier-based fighter) Claude
 * Mitsubishi A6M (Navy Type 0 Carrier Fighter) Zeke
 * Kawanishi N1K-J/N1K2-J (Navy Land based Interceptor Fighter 'Shiden'/'Shiden Kai') George
 * Mitsubishi J2M Raiden (Land based fighter) Jack
 * J1N1-S (Navy Night Fighter 'Gekko') Irving

Bombers:
 * Yokosuka P1Y (Navy bomber Model 11 'Ginga') Frances
 * Mitsubishi G4M (Type 1 land-based attack aircraft) Betty
 * Mitsubishi G3M (Type 96 Land-based Attack Aircraft 'Rikko') Nell

Torpedo & Dive Bombers:
 * Aichi D1A (Navy Type 94 Carrier Bomber) Susie
 * Aichi D3A (Navy Type 99 Carrier Bomber) Val
 * Yokosuka D4Y (Navy Type 33 Carrier Bomber 'Suisei') Judy
 * Nakajima B5N (Navy Type 97 Carrier Attack Bomber) Kate
 * Nakajima B6N (Navy Type 11 Carrier Attack Aircraft 'Tenzan') Jill
 * Yokosuka B4Y (Navy Type 96 Carrier Attack Aircraft) Jean

Float planes & Flying Boats
 * Aichi E13A (Navy Type 0 Reconnaissance Seaplane) Jake
 * Yokosuka E14Y (Type 0 Small Reconnaissance Seaplane) Glen
 * Aichi E16A (Navy Type 16 Reconnaissance Seaplane 'Zuiun') Paul
 * Mitsubishi F1M (Type 0 Observation Seaplane) Pete
 * Nakajima E8N (Navy Type 95 Reconnaissance Seaplane) Dave
 * Kawanishi E7K (Navy Type 94 Reconnaissance Seaplane) Alf
 * Kawanishi H8K (Type 2 Large Flying Boat) Emily
 * Kawanishi H6K (Type 97 Large Flying Boat) Mavis
 * Kawanishi N1K1 (Navy Fighter Seaplane 'Kyōfū') Rex
 * Nakajima A6M2-N (Navy Type 2 Interceptor/Fighter-Bomber) Rufe

Reconnaissance Planes:
 * Nakajima C6N Myrt

Trainers:
 * Mitsubishi A5M-4k (2 seat version of Mitsubishi A5M)

Transports:
 * Mitsubishi Ki-57 (Type 100 Transport Model 2 Topsy
 * Nakajima Ki-34 (Navy Type AT-2 Transport) Thora
 * Nakajima G5N (Experimental 13-Shi Attack Bomber) Liz (used as transports)

Carrier aviation flotillas
The elite of the pilots were the carrier-based air groups (kokutai, later called koku sentai) whose size (from a handful to 80 or 90 aircraft) was dependent on both the mission and type of aircraft carrier that they were on. Fleet carriers had three types of aircraft: fighters, level/torpedo planes, and dive bombers. Smaller carriers tended to have only two types, fighters and dive bombers. The carrier-based kokutai numbered over 1,500 pilots and just as many aircraft at the beginning of the Pacific War.

Eleventh Air Fleet and land-based air fleets
The IJN also maintained a shore-based system of naval air fleets called Koku Kantai and area air fleets called homen kantai containing mostly twin-engine bombers and seaplanes. The senior command was the Eleventh Naval Air Fleet, commanded by Vice Admiral Nishizō Tsukahara. Land based aircraft provided the bulk of Japan's naval aviation up to the eve of World War II.

Strength
Each naval air fleet contained one or more naval air flotillas (commanded by Rear Admirals) each with two or more naval air groups. Each naval air group consisted of a base unit and 12 to 36 aircraft, plus four to 12 aircraft in reserve. Each naval air group consisted of several hikotai (squadron/s) of nine, 12 or 16 aircraft; this was the main IJN Air Service combat unit and was equivalent to a  chutai  in the Imperial Japanese Army Air Service. Each hikotai was commanded by a Lieutenant (j.g.), Warrant Officer, or experienced Chief Petty Officer, while most pilots were non-commissioned officers. There were usually four sections in each hikotai, and each section (shotai) with three or four aircraft; by mid-1944 it was common for a shotai to have four aircraft. There were over 90 naval air groups at the start of the Pacific War, each assigned either a name or a number. The named naval air groups were usually linked to a particular navy air command or a navy base. They were usually numbered when they left Japan.

And before 31 October 1942

 * Place name; Standing air group (常設航空隊, Jōsetsu-Kōkūtai).
 * Numbered name; Special setting air group (特設航空隊, Tokusetsu-Kōkūtai).

And after 1 November 1942

 * Numbered name; Category 'A' air group (甲航空隊, Kō Kōkūtai) as combatant unit.
 * Example
 * 12th Kōkūtai is Training (bomber) group.
 * 121st Kōkūtai is reconnaissance aircraft group.
 * 762nd Kōkūtai is land-based torpedo bomber group.
 * 1081st Kōkūtai is military airlift group.
 * Regulation table


 * Place name; Category 'A' air group as training unit, evaluation unit.
 * Example
 * Atsugi Kōkūtai
 * Kasumigaura Kōkūtai
 * Takuma Kōkūtai
 * Yokosuka Kōkutai
 * Region name; Category 'B' air group (乙航空隊, Otsu Kōkūtai) as air base guard unit.
 * Example
 * Kantō Kōkutai
 * Mariana Kōkutai
 * Hitō Kōkutai

And after 1 March 1944

 * Regulation table

Naval Aircraft identification System
The IJN had, at the beginning of the Pacific War, three aircraft designation systems: The Experimental Shi numbers, the Type numbering system and an aircraft designation system broadly similar to that used by the U.S. Navy from 1922 until 1962.

Each new design was first given an experimental Shi number, based upon the current Japanese imperial year of reign. The Mitsubishi Zero so started its career as '''Navy Experimental 12-Shi Carrier Fighter.

Upon entering production the aircraft was given a Type number. The 'Zero' was so fully known as Navy Type 0 Carrier Fighter, as the Zero was accepted in 1940, or 2600 in the Japanese calendar.

The aircraft was also given a "short designation" consisting of a group of Roman letters and numbers. (G4M designated attack bomber (G), the fourth in the Navy's sequence, designed or produced by Mitsubishi, while G5N would be the next attack bomber in sequence, built by Nakajima.)
 * The first letter (sometimes two) indicated the basic type or purpose of the aircraft.
 * Second came a series number indicating the number of major sub-types produced for that type of aircraft. (Unlike USN practice, the digit "1" was not ignored in this system and was included.)
 * Third was the second letter which was the manufacturer's code, and included some non-Japanese companies.
 * Fourth was a number indicating the version of the aircraft.

The first production version of the 'Zero' thus became A6M1.

Further minor changes were indicated by adding letters after the subtype number as in the Type/Model scheme above. The first two letters and the series number remained the same for the service life of each design.

In a few cases, when the designed role of an aircraft changed, the new use was indicated by adding a dash and a second type letter to the end of the existing short designation (e.g., the H6K4 was the sixth flying boat (H6) designed by Kawanishi (K), fourth version of that design (4). When the plane was equipped primarily as a troop or supply transport, its designation was H6K4-L.)