The Zero was exciting, like nothing I’d seen before. Even sitting on the ground she had the most gracious lines of any fighter I’d ever laid eyes on.
We were finally given a fully enclosed cockpit, a powerful engine and retractable landing gear. In place of Claude’s two light machine guns (Mitsubishi A5M Claude – author’s note) the Zero carried two guns and a pair of 20 mm cannons. She was also twice as fast as the Claude and had double the Claude’s range. For a fighter pilot it was simply a dream come true. Of all types I had a chance to fly, the A6M2 was the most responsive and easy to handle. The flight controls moved in response to even the slightest input. This is how the Japanese ace Saburo Sakai remembered his first encounter with the Mitsubishi A6M Reisen, perhaps the best known Japanese World War II fighter type. The Zero saw action in practically all battles waged by the Imperial Japanese Navy, from the attack on Pearl Harbor all the way through the defense of the Home Islands against the B-29s. During the first months of the war in the Pacific the Zero emerged as a world-class fighter, unrivalled in the air by anything the enemy could muster. However, with no worthy successor in sight, by 1943 the Zero was all but obsolete. Despite that, Japanese factories continued to build and deliver the type until the end of the war. The Reisen (Zero) didn’t simply emerge out of thin air. The birth of this supreme fighter was preceded by years of experimentation by the Imperial Japanese Navy with a new type of combat machines – carrier-based fighters.
Expansion of the Imperial Japanese Navy carrier aviation post World War I
The Great War wreaked havoc with the economies of even the most powerful nations. Japan was no exception: strapped for cash, the Empire had to put on hold the development of naval aviation assets. Which is not to say that the expansion of the Imperial Japanese Navy ground to a halt altogether. In May 1917, when the war was still going on, the ambitious Hatchi Kantai Kansei Keikaku fleet expansion program was launched (also known as the 8-4 program), designed to achieve parity in naval strength with such giants as Great Britain or the USA. The plan was to build and commission a fleet of 63 ships of various classes, with eight battleships and four battlecruisers at the core of the armada. 1920 saw the expansion of the 8-4 program to include four additional battlecruisers. The cost of this massive undertaking didn’t leave a lot of margin for the development of naval aviation, especially since the Navy brass viewed powerful and heavily armed warships far superior to naval aircraft, whose combat value at that time was rather insignificant.
Nonetheless, the Japanese closely followed the developments of naval aviation elsewhere in the world. When Lt. Cdr. Yozo Kaneko submitted his report concerning early trials of conventional aircraft launches from the decks of warships, a decision was quickly made to perform similar tests in Japan. On June 22, 1920 Lt. Torse Kubawara took-off in a Sopwith Pup from a launch platform mounted on the foredeck of the seaplane carrier Wakamiya Maru. Later on similar trials were run using the cruiser Kiso and battleship Yamashiro. Lessons learned from those tests led to a conclusion that newly constructed heavy warships must be equipped with launch platforms. A need for the construction of an experimental aircraft carrier was also raised.
The latter idea received a significant boost after the Washington conference, convened following a U.S. proposal to address issues in the Far East and to seek limitations in naval shipbuilding programs. Based on the treaty signed on February 6, 1922 the maximum total tonnage for U.S. and British fleets of capital ships was set at 500,000 tons, 300,000 tons for Japan and 175,000 tons for French and Italian navies (those limits were subsequently raised). A maximum displacement of a capital ship was set at 35,000 tons and the caliber of main battery guns was limited to 16 inches (406.4 mm). Parties also agreed that allowable tonnage of capital ships must not exceed 50 percent of the entire fleet.
All the remaining types of warships were treated as a single category and each nation was allocated the following tonnage limits for surface vessels and submarines: USA and Great Britain – 450,000 and 90,000 tons, Japan 270,000 and 54,000 tons. Interestingly, the latter category didn’t include warships capable of launching aircraft. Both the U.S. and Great Britain were allowed to operate such vessels with the aggregate tonnage of 80,000 tons, while Japan’s limit was set at 48,000 tons.
Other provisions of the treaty included the minimum age after a vessel could be replaced with a new unit, as well as limitations on construction and development of naval bases. The agreement appeared to have paved the way for a gradual reduction of naval weapons, but it soon proved not to be the case. While the treaty resulted in a freeze on battleship construction, lighter vessels were in fact being built in ever greater numbers.
A separate article of the treaty was devoted to aircraft carriers. The participating nations agreed that the maximum displacement for a warship of that class must not exceed 27,000 tons and the number of main battery guns carried by such ships was limited to ten with a maximum caliber of 203 mm. No limits were imposed on smaller caliber weapons. Each of the five signatories of the treaty was allowed to convert up to two capital ships (or line cruisers that otherwise would have been scrapped) into aircraft carriers. The only stipulation was that the displacement of the units used for conversion should not exceed 33,000 tons and the number of 203 mm guns carried by the ships was limited to eight.
The Japanese admiralty were thoroughly satisfied with the possibilities that the treaty opened up for their navy. Japan had the third largest fleet in the world (after the U.S. and Great Britain), second in the Pacific and the first in the Far East. Construction and commissioning of a fleet of aircraft carriers would provide the Japanese commanders with a long-range air reconnaissance capability in support of their line squadrons. The Washington Treaty spelled doom for the ambitious battleship construction programs, but at the same time jump-started rapid development of naval aviation.
Construction of the first Japanese aircraft carrier had begun even before the Washington Treaty was signed. Hosho was launched on 13 November, 1921 at Asano Shipbuilding Co. in Tsurumi and entered service on December 7, 1922. It was a relatively small ship, displacing 7,470 tons, 167.9 m long and 18 m wide. However, Hosho was a thoroughly modern vessel. She featured a flight deck unimpeded by any superstructures, unlike the British Furious and Vindictive carriers of the same period. Although there were plans to build Hosho’s sister ship, they were abandoned in 1922 since the provisions of the Washington Treaty allowed a much better option – conversion into aircraft carriers of two large armored ships.
In March 1923 Japanese government launched a new fleet development program taking into account the outcomes of the Washington Treaty. Imperial Japanese Navy command ordered conversion of two battlecruiser hulls (Akagi and Amagi) into aircraft carriers. Akagi was laid down on December 6, 1920, followed ten days later by Amagi. In September 1923 the Great Kanto Earthquake struck Japan, which damaged the unfinished Amagi hull beyond repair. In early 1924 battleship Kaga was selected for conversion to aircraft carrier replacing the lost Amagi.
In those early days aircraft carriers were not considered true combat ships, but rather auxiliary vessels providing little more than long-range air reconnaissance capabilities for naval combat teams. Gathered intelligence would allow the commanders to make informed decisions to either engage comparable or weaker enemy, or to avoid contact in the face of superior enemy forces. This way of thinking was fully understandable in the 1920s, since carrier-based aircraft of the period were in fact land-based machines merely adapted to service at sea. Also in those days enemy force consisting of more aircraft carriers than battleships was considered less intimidating than the other way around. Following this logic, the Japanese thought it was more prudent to keep the Akagi and Kaga, even converted to aircraft carriers, than risk losing them altogether. Following the conversion, the ships entered service in 1927 (Akagi) and 1928 (Kaga).
It wasn’t long before the IJN high command fully appreciated the value of aircraft carriers in future war in the Pacific and they wasted no time placing orders for more vessels of that type. The light aircraft carrier Ryujo joined the fleet in 1933, followed by Soryu (1937) and Hiryu (1939).
The need to develop purpose-built aircraft to operate from decks of new carriers soon became apparent. However, the Japanese aircraft manufacturers had little experience in design of carrier-based machines, so drawing from foreign experience became the only option. A breakthrough in the history of IJN naval aviation was arrival in April 1921 of the Sempill Mission which comprised a team of thirty naval aviation experts. It wasn’t the first time that the British lent their expertise to Japanese aviation. A year earlier a group of British Short Brothers engineers accepted the invitation of the IJN to help in mastering manufacturing techniques of the Felixstowe F.5 flying boat. The Sempill Mission brought with them modern combat aircraft and trainers, including the Avro 504K, Gloster Sparrowhawk, Sopwith Cuckoo, Parnall Panther, Blackburn Swift, S.E.5A, De Havilland D.H.9, a Short seaplane, as well as Supermarine Channel and Short Felixstowe F.5 flying boats. The Sempill Mission instructors help modernize IJN flight and ground crew training and produced a blueprint of the Japanese naval air arm’s organizational structure. The establishment of a Temporary Naval Flight Training Troop, led by Rear Admiral Tadaji Tajiri and staffed by British instructors, was also a British idea. The unit operated out of Kasumigaura (land-based aircraft) and Yokosuka (seaplanes and flying boats).
The British instructors remained in Japan for 18 months and trained Japanese aircrews in air navigation, reconnaissance operations, torpedo bombing and aerial photography, laying solid foundations for the future of the Japanese naval air arm. Initially all flight training was performed using British aircraft, but those were soon replaced with indigenous license-built machines. Nakajima obtained a license to build Avro 504K/L trainers, while Aichi acquired the manufacturing rights for the Felixtowe F.5 flying boat, which was also manufactured at Hiro and Yokosho Arsenals. At the same time Mitsubishi approached the British Sopwith Aircraft Co. seeking help in designing aircraft for Hosho air wing. Soon a team of Sopwith engineers, led by Herbert Smith, arrived in Japan to work on the project. Other Japanese aircraft manufacturers were also actively looking for foreign partners: Nakajima enlisted help of French firms Breguet and Nieuport, while Kawanishi cooperated with the British Short. Kawasaki invited experts from Germany, who were more than happy to accept employment overseas when the Treaty of Versailles greatly limited their earning potential at home. As can be clearly seen, the Japanese weren’t shy seeking foreign assistance in the development of their own naval air arm. However, while the Japanese manufacturers had little difficulty adopting modern airframe construction technologies imported from Europe, they struggled with powerplants. Most of the contemporary Japanese designs were powered by Lorraine, Hispano-Suiza or Napier engines. To move forward in that department required time.
Head of Mitsubishi, Koyota Iwasaki, understood that the development of modern naval aircraft wouldn’t be possible without foreign expertise and the only nation that seemed to have the necessary know-how was Great Britain. In early 1921 he invited Sopwith’s Herbert Smith, whose resume included the design of such excellent aircraft as the Camel and the Pup, to visit Mitsubishi’s new plant in Nagoya. Smith’s arrival may have had something to do with the fact that in 1920 Sopwith Aviation Company struggled financially and went bankrupt in short order. Those developments left Smith and his team unemployed, so the timing of the Japanese invitation couldn’t have been better. The Japanese paid much more generously than what Smith’s team could have hoped for back home, but the task ahead was also formidable. A team of seven British engineers was expected to design all types of aircraft (fighter, reconnaissance platform and a torpedo bomber) to be included in the Hosho air wing. Those would be the world’s first purpose-built carrier-based aircraft. The aircraft in service with the Royal Navy were simply land-based designs adapted to carrier operations. Also, at that time, Japan had no tender system in place and government contracts were simply granted to one of the aircraft manufacturers. That was a reflection of a weakness of Japanese aircraft manufacturing sector. Later on the government introduced a system requiring a publication of tactical and technical requirements (Shi), which led to a number of designs developed by different companies competing for the contract.
The British team designed the 1MF fighter and 1MR reconnaissance aircraft, which were both approved for full-scale production, but the 1MT torpedo bomber was a complete flop.
It might be worthwhile at this point to take a closer look at Japanese aircraft industry, whose beginnings were rather unimpressive. Inter-service rivalry and lack of cooperation between the Imperial Japanese Navy and Army resulted in squandering of limited resources amidst attempts by both services to create their own, independent air arms. Not surprisingly, it did little to help the fledgling industry to grow. Contradictory requirements received by the industry led to the development of a multitude of aircraft types, all suffering from various shortcomings. It wasn’t until two major industrial players – Mitsubishi and Kawasaki – entered the arena that development of aircraft manufacturing base began to pick up pace. Also significant was the founding of Nakajima (future leader of aircraft industry) by Mitsui.
Until 1925 the entire output of Japanese aircraft industry was based on technologies obtained overseas, mainly from France, Great Britain, Germany and the USA. This imported know-how not only greatly accelerated the development of local aircraft industry, but also allowed Japanese engineers access to U.S. universities and the best technical institutes. In the early 1930s government guidelines recommended that Japanese aircraft manufacturers should base their work on locally-developed technological processes, although using foreign know-how was not entirely discouraged. The new approach proved to be a success to the point that by 1936 Japanese aircraft manufacturers not only became independent of imported technologies, but also began to crank out aircraft designs, such as Mitsubishi G3M, Ki-15, A5M or Nakajima B5N, that were on par with their foreign counterparts, if not better. This rather remarkable development went largely unnoticed by the leading world powers as they continued to view Japan as an insignificant Asian nation, capable of little more than copying foreign ideas, with the economy well known for mass production of cheap, low quality products.
First Japanese carrier-based fighter aircraft
In the early 1920s the mainstay of the IJN air arm was the Gloster Sparrowhawk biplane fighter. Fifty examples of the aircraft were built for the Japanese at Gloster Aircraft Company, while another forty were assembled using imported components at Yokosuka Arsenal. The aircraft soldiered on in Japanese service until 1928. Most of them operated from land bases, but several examples were used in tests using a launch platform mounted on top of a main battery turret of the battleship Yamasiro. Some (probably ten examples) were modified for carrier operations, although they were never used in that configuration having been superseded by a more modern fighter type built by Mitsubishi.
The design of the Mitsubishi 1MF and delivery of the fighter’s prototype took the British team led by Herbert Smith only several months. The aircraft made its first flight in 1921.
The Mitsubishi 1MF1, officially designated “Navy Type 10 Carrier Fighter”, was a design typical for its time. This all-wood, fabric-covered biplane was powered by the eight-cylinder, liquid-cooled Hispano-Suiza 8 engine developing 300 hp. The powerplant was in fact license-built in Japan under designation Mitsubishi Type Hi. Offensive armament was mounted above the engine and consisted of two 7.7 mm Vickers machine guns. The first prototype featured a front-mounted radiator, which was responsible for the fighter’s characteristic “boxy” nose. Later versions of the fighter were equipped with a twin Lamblin radiators mounted between the landing gear struts. Another feature characteristic of the 1MF1 and absent in later versions (which also featured greater wingspan) was the “ear” or extended ailerons similar to the Fokker DVII. The 1MF1 designation stood for a single-seat aircraft (“1”), manufactured by Mitsubishi (“M”), fighter type (“F”), first production version (“1”). The 1MF2 version, which went into full-scale production, featured increased vertical stabilizer area.
The 1MF3 variant saw the installation of the Lamblin radiators, which resulted in a more streamlined shape of the fighter’s nose section. One of the sub-variants, the 1MF3a, featured a redesigned vertical stabilizer, which well concealed the type’s Sopwith pedigree. Other, often minor modifications were also introduced, among them position lights on wingtips (a first in a Japanese design!). Some sources claim that the aircraft earmarked for carrier operations had their “claws” mounted on wheel axles removed and replaced with proper arresting hooks attached to the tail skid. More substantial changes were introduced in the 1MF4 version of the fighter. One of them was moving the cockpit forward to better manage the aircraft’s center of gravity. This resulted in the cockpit placed directly underneath the top wing, which would have greatly limited visibility. In order to compensate for that, a large cutout was introduced in the top wing.
The final iteration of the fighter was the 1MF5 and its training derivative 1MF5a. Among modifications introduced in that version was jettisonable landing gear and two cigar-shaped floats underneath the lower wing, which were supposed to keep the aircraft afloat in the event of an emergency water landing.
On February 28, 1923 the flight deck of the newly commissioned aircraft carrier Hosho was used in the first successful launch and recovery of an aircraft. At the controls of a 1MF3 was William Jordan, a member of Herbert Smith’s team and Mitsubishi’s chief test pilot. A month later Lt. Shunichi Kira became the first Japanese aviator to have performed a launch and recovery on an aircraft carrier.
In order to improve the aircraft’s directional control on a relatively narrow flight deck, a dozen or so cables were strung along the deck. Those were supposed to keep the aircraft from veering off the desired track. It soon became clear that the system was neither practical, nor useful and the whole idea was abandoned. In its place a system of three sets of lamps was adopted (red, yellow and green), which were carefully arranged at very specific angles, so that only one row of lights was visible to the pilot, depending on the aircraft’s relation to the glideslope. The system worked extremely well and its basic principle is used to this day in “meatballs” installed on flight decks of modern US Navy carriers.
Beginning in late 1923 1MF3 fighters were permanently embarked on Hosho and in 1927 the type was also assigned to Akagi, followed by Kaga in 1928.
Type 10 fighters were manufactured until 1929. In total, 138 examples of the type were produced, including the prototypes and trainer versions. The first Japanese carrier-based fighter proved to be a robust design, easy to handle and very forgiving in the air. The Type 10 never saw combat before it was withdrawn from service in 1930 and replaced by the Type 3 (Nakajima A1N). Some of the ex-navy examples were sold to civilian operators, who continued to use them in a variety of roles. The Mitsubishi 1MF was the world’s first purpose-built carrier-based fighter.
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