Nakajima Ki-43 Hayabusa Vol. I

Nakajima Ki-43 Hayabusa Vol. I

Nakajima K-43 Hayabusa, code-named Oscar by the Allies, was the Imperial Japanese Army’s equivalent of the Zero fighter in service with the Imperial Navy.

In combat units the machine replaced the aging Ki-27. Manufactured in large numbers, the fighter remained in frontline service until the end of the war. By the time its final version entered production, the development of its successor – the Ki-84 – had already started. The Ki-43 was a very maneuverable machine, but in many areas it was inferior to its adversaries. Despite its fragile design, poor armament and almost no armored protection, the Ki-43 was well-liked by the Japanese pilots and it became a symbol of the Imperial Japanese Army Air Service. Hayabusa was the pinnacle of the Japanese fighter design development until the lessons learned in the Pacific laid the ground for new approaches to the construction of tactical aircraft.

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Before the Ki-43 was designed

During the interwar period there was no independent air arm in Japan. Instead, both the Army and the Navy had their own air services, subordinated directly to their respective high commands. This state of affairs lasted in an unchanged form from the very inception of Japanese military aviation until the Empire’s capitulation in 1945. While similar arrangements in other countries typically produced a dose of healthy inter-service competition, in Japan it resulted in the total lack of cooperation between the Army and the Navy, no holds barred competition for limited resources and wasteful, often duplicate, armament development programs. It wasn’t uncommon to find two different designs in service with the Navy and the Army, which were virtually identical in terms of their performance characteristics and combat capabilities.
In the second half of the 1930s Japanese aircraft designers worked diligently on the development of light, extremely maneuverable fighter types. In order to achieve that goal the aircraft had to be as light as possible, with its structural strength reduced to a bare minimum. By the same token the emerging designs were very lightly armored and featured lightweight armament. Until the mid-1930s Japanese fighters were typically armed with a pair of 7.7 mm machine guns, which were fine against light fighters, but very ineffective in confrontations with sturdy, modern bombers.


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This approach to the fighter design was perhaps the reflection of the deep appreciation of the mastery of one’s craft, so highly regarded in the Japanese culture. If an air-to-air engagement was to be decided in a close-in dogfight, then the pilot who emerged victorious, thanks to his superior skills, would be worthy of utmost respect. At the same time the European air combat doctrine had already moved on, focusing on speed and firepower as the key ingredients of success, rather than maneuverability. Lessons learned in the Spanish Civil War seemed to prove those ideas right. There were quite a few enthusiastic supporters of the European approach to air combat in Japan, but they were outnumbered by the conservatives, who eventually had a final say on the development of the Japanese air arm. It wasn’t until the Japanese began to suffer huge losses over the Pacific that the key decision makers within the Air Force saw a need for a different approach, but by that time it was too late to start development of new designs and to press them into service.
Within the Imperial Japanese Army, fighter aviation was supposed to provide support for bomber formations operating close to the frontlines and to ensure local air superiority. Fighters were never intended to provide close air support to ground troops as the role was assigned to a wide range of light bomber types. It is then no wonder that the Army’s specifications for fighter aircraft had remained unchanged for years, always stressing excellent tactical characteristics and maneuverability as the key features of the design. This approach seemed to work just fine in China, where the Japanese easily dominated their adversaries in the air. A hero of those battles was the Ki-10 biplane, followed by the Nakajima Ki-27, which became the basic Army fighter type when it went into service in 1937.

The Ki-27 – the first all-metal fighter with a fully enclosed cockpit to see service with the Imperial Japanese Army Air Service (Dai Nippon Teikoku Rikugun) – was a thoroughly modern design, equal to, or even better than, many of its foreign contemporaries. The design went through a lengthy period of testing before it emerged as a winner in the Army fighter competition, having beaten the rival Mitsubishi and Kawasaki designs. It was a single-seat, low-wing monoplane of all-metal construction with fixed landing gear featuring streamlined spats and an extensively glazed canopy, which provided excellent visibility in all directions. Thanks to its superlight airframe, the Ki-27 was almost as maneuverable as biplane fighters, but it lacked armored protection and self-sealing fuel tanks. The machine was armed with a pair of Type 89 7.7 mm machine guns, which provided enough punch to deal with fabric-covered Chinese fighters, but were woefully inadequate against bombers. Nonetheless, the new fighter quickly began to make its mark in the skies above China and Manchuria until it met its match over Khalkhin Gol in 1939 when it was challenged by the fast and agile Polikarpov I-16 fighters flown by Soviet pilots.
Fighter design competitions were a fixture in Japan until the late 1930s, but the relentless drive to keep up with the rest of the world put an enormous pressure on the aircraft manufacturers. When it came to selecting the successor of the Ki-27, the Army decided another full-blown competition would be too costly and time consuming, not to mention unnecessary pressure it was going to put on the industry. Mitsubishi was at that time busy working on several programs, including the development of the future naval fighter (A6M Zero), while Kawasaki, although experts in inline engines design, didn’t have an available powerplant suitable for the future Army fighter. The Army was thoroughly happy with the Ki-27, which is why the request for its successor (designated Ki-43 in 1937) eventually went to Nakajima, who had already gained a lot of experience in modern fighter design and had become a de-facto dedicated supplier of combat aircraft for the Army.

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Tactical and technical requirements of the new fighter clearly showed that the Army was very much fond of their Ki-27. The Ki-43 was expected to be just a little bit more capable than its predecessor, while maintaining its superior maneuverability. In fact, the Army probably would have been perfectly happy with an upgraded version of the Ki-27 featuring retractable landing gear, but by that time the idea of operating a universal fighter type had already been abandoned in favor of fielding a range of specialized aircraft.
Soon the work began at Koku Hombu on a very ambitious procurement program (Koku Heiki Kenkyu Hoshin), whose goal was the development of a new generation of combat aircraft to replace the machines currently entering service. The program called for the development of light and heavy single-seat, single-engine fighter aircraft. The “heavy” and “light” designations didn’t refer to the fighters’ weight, but rather to the firepower. The light single-engine fighter (kei tenza sentoki, or keisen) was supposed to have exceptional maneuverability and armament consisting of two 7.7 mm machine guns (which happened to be a standard armament suite of all Japanese fighters). This combination of offensive punch and performance characteristics would make it an ideal platform against enemy fighters. In this role, speed and range weren’t considered critical. The heavy single-engine fighter to be developed under the program (ju tanza sentoki, or jusen) was to be armed with a pair of 7.7 mm machine guns, in addition to one or two cannons, which were in fact heavy caliber machine guns (the Army classified all weapons of up to 11 mm as machine guns, while anything above 11 mm was considered a cannon). The heavy fighters would be tasked with combating enemy bombers – a role that required a decent speed and climb performance, even at a cost of range and maneuverability. Once the program was officially adopted, the usual practice of prototype fly-offs was abandoned in favor of approaching individual manufacturers to submit their designs.

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The Koku Heiki Kenkyu Hoshin program notwithstanding, in early 1937 Kawasaki, Nakajima and Mitsubishi were invited to take part in a competition for a twin-engine interceptor armed with cannons, which eventually led to the introduction of the Kawasaki Ki-45 Toryu. Since the Ki-45 program ran into all kinds of teething problems, the Army’s Technical Department (Rikugun Koku Hombu) decided to approach Nakajima to develop a fast, single-seat interceptor (the future Ki-44 Shoki). As a result, when the war broke out, the Army had three different fighter types either in service, or in development: the maneuverable Ki-43, Ki-44 interceptor and Ki-45 heavy fighter. The successor of the Ki-27 (the Ki-43) was classed as a light fighter, which meant some of the performance parameters originally formulated for the design could be relaxed.
There are several reasons why the Japanese Imperial Army chose that particular path of the development of their air arm. While the new take on the combat use of fighter aircraft quickly reached Japan and gained popularity among some of the decision makers, the conservative faction prevailed and firmly stood by their samurai-era ethos of single-warrior combat.
Another factor was the tactical role of the fighter. The spearhead of the Army’s air arm was a formation of close or medium range bombers providing both offensive and defensive support for ground troops. The role of fighter aircraft was to protect the bombers and achieve air superiority in the local area. In order to successfully perform the task, the fighters needed to be highly maneuverable, easy to maintain and capable of operating from unprepared, frontline airfields.
The Imperial Japanese Army Air Service was also responsible for air defense of the country, which required fast and heavily armed interceptors capable of effectively engaging modern long-range bombers.

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Offensive air operations were almost entirely delegated to the Navy, which was tasked not only with conventional carrier operations, but also with long-range missions deep into enemy territory, often requiring long flights over open ocean. It is no wonder that naval fighters were expected to have exceptional flight endurance characteristics.
Yet another factor was the limited choice of aircraft engines. Despite great efforts, Japanese manufacturers hadn’t been able to achieve progress in this area on par with their U.S. and European counterparts. This was especially true in the case of high-powered motors, which were in a notoriously short supply. This gave the Japanese aircraft designers a real headache each time they were forced to pick a powerplant for their new machine from a very short list of available engines. It didn’t make their lives any easier when the Navy’s or Army’s technical departments insisted on the use of a particular powerplant for each new design.
In practice the Army and the Navy obtained varying results using these sets of principles and guidelines in the development of their air arms. The Navy wanted their fighters to have a long-range capability, combined with a good speed performance and agility. This set of requirements presented aircraft designers with an almost impossible task of squeezing all those capabilities into a small airframe of a carrier-based fighter. Unbelievably, they rose to the challenge and delivered the sensational A6M Zero – a world-beating design of its time. That success, however, came at a price. From the very beginning the A6M was engineered to the very limits, leaving no margin for upgrades or further development. As a result, half way through the war the Zero had become obsolete and could no longer pose a threat to the newest U.S. and British aircraft. However, it has to be said that in the late 1930s it wasn’t easy to predict that course of events.
The concept of a universal fighter platform, capable of performing a wide range of tactical missions, was not widely accepted in the Army. Rapid development of air combat doctrines in France, Germany and other countries had a serious impact on the Japanese strategists, who believed a single fighter design wasn’t enough to perform a multitude of combat missions. This led to a breakthrough decision to launch the development and production of three fighter aircraft with specialized roles to perform. The Nakajima Ki-43, developed under the same set of requirements as its predecessor (the Ki-27), would become the basic fighter type in Army units. It is no wonder that its lead designer was Hideo Itokawa, the “father” of the Ki-27.

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