Imperial Japanese Navy Air Service

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 be 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 of 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 Harbor 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 Japan 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.

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 Mitsubishi G3M and Mitsubishi 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 for strategic bombing and operated long ranged bombers.

The Japanese strategic bombing was 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.

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 (Imperial Japanese Navy): 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 by destroying over 188 aircraft and only losing 29 of their own 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 Darwin in northern Australia.

In these battles, the Japanese veterans of the Chinese war did well against inexperienced Allied pilots flying obsolescent aircraft. However, their advantage did not last. In the Battle of the Coral Sea, the Battle of Midway, and again in the Guadalcanal Campaign, the Japanese lost many veteran pilots. Because the Japanese pilot training program was unable to increase its production rate, those veterans could not be replaced. Meanwhile, the American pilot training program went from strength to strength. The American aircraft industry rapidly increased production rates of new designs that rendered their Japanese opponents obsolescent. Examination of crashed or captured Japanese aircraft revealed that they achieved their superior range and maneuverability by doing without cockpit armor and self-sealing fuel tanks. Flight tests showed that they lost maneuverability at high speeds. American pilots were trained to take advantage of these weaknesses. The outdated Japanese aircraft and poorly trained pilots suffered great losses in any air combat for the rest of the war, particularly in the Great Marianas Turkey Shoot. In the Battle of Leyte Gulf a few months later, the First Air Fleet was used only as a decoy force to draw the main American fleet away from Leyte. The remnants of Japanese naval aviation were then limited to land-based operations, increasingly characterized by kamikaze attacks on American invasion fleets.

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

Aircraft strength 1941

The IJNAS had over 3,089 aircraft in 1941 and 370 trainers.

World War II Aircraft

Fighters:

Bombers:

Torpedo & Dive Bombers:

Float planes & Flying Boats

Reconnaissance Planes:

Trainers:

Transports:

Carrier aviation flotillas

The elite of the pilots were the carrier-based air groups (Kōkūtai, 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 Kōkūtai 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

And after 1 November 1942

And after 1 March 1944

Naval Aircraft identification System

The IJN had, at the beginning of the Pacific War, three aircraft designation systems: The Experimental Shi （試）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 （海軍十二試艦上戦闘機）.

Upon entering production the aircraft was given a Type number. The 'Zero' was so fully known as Navy Type 0 Carrier Fighter （海軍零式艦上戦闘機）, 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 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.)