Mitsubishi A5M Claude

The mid-1930s saw the ever increasing numbers of fast monoplane fighters entering service with many of the world’s air forces.

This was not the case in naval aviation, where biplane designs still reigned supreme. One exception to the rule was the French Navy with its aircraft carrier Bearn and embarked Dewoitine D.371T1 fighters in parasol configuration, hardly a promising design for carrier-based aircraft. Prevalence of biplanes among naval fighters of the time was due to very strict limitations on landing speeds imposed by small flight decks of contemporary aircraft carriers. It was in the middle of that decade, in 1935, that the Mitsubishi A5M entered the stage – a low-wing, monoplane carrier-based fighter, which set new standards for aircraft of its class. Having said that, the Claude wasn’t the first fighter in this configuration designed for the Imperial Japanese Navy.

A5M was born
In the early 1930s the Imperial Japanese Navy Air Service underwent radical overhaul which included the launch of a special aircraft design development program, championed by admirals Matsuyama and Yamamoto. The program’s goal was to build an indigenous and fully independent aviation industry to fulfil the Navy’s needs following lessons learned in the Sino – Japanese conflict of 1932.

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The first and foremost goal of the program (designated 7 Shi) was to deliver new designs for the IJN based on the technical requirements provided by Kaigun Koku Hombu in several basic categories of carrier-based aircraft: fighter, dive bomber, torpedo bomber and reconnaissance floatplane. Official requirements set the bar very high for new aircraft designs, which were expected to be superior to the most advanced machines in each category in service with foreign navies. In order to ensure success of the program, Japanese aviation industry received the highest priority status and generous government funding.
Required specifications for the carrier-based fighter under the 7 Shi program were as follows: maximum speed at 3,000 m – from 335 to 370 km/h; time to climb to 3,000 m – no more than four minutes; wingspan – not exceeding 10.25 m. The latter was dictated by the dimensions of aircraft elevators used on IJN carriers. The future aircraft was to be a successor to the Nakajima A1N fighter – the mainstay of the Japanese carrier aviation at the time. Nakajima and Mitsubishi were approached to submit their bids in the design competition, with the winner to receive a contract for a full-scale production.
For Mitsubishi the competition was of vital importance as it offered the company a chance to regain its status of the lead contractor to the Imperial Japanese Air Service which it had lost when Nakajima A1N entered service. As soon as the formal invitation was received Mitsubishi management formed a design team led by Jiro Horikoshi, who had been working for the company since 1928. Horikoshi’s design was to vindicate Mitsubishi’s loss of prestige and bring the company good fortune. Horikoshi had spent years studying in Europe and in the USA, where he gained invaluable insight into the most advanced aircraft design technologies. Although still a relatively inexperienced designer, Horikoshi wasted no time and quickly produced several preliminary design concepts of biplanes and high-wing monoplanes, but in the end he settled for a modern cantilever low-wing monoplane, since only that configuration could possibly achieve the required speed performance.
The new aircraft was visually similar to the Boeing P-26 – a cantilever, low-wing monoplane with elliptical inverted gull wing. The low-drag airfoil was also relatively simple to manufacture. In order to minimize the wing’s bending moments in recovery from dives, the American M-6 airfoil was used, which later became a staple of many Japanese designs.

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Fabric-skinned fuselage featured a welded tube frame. The wing’s structure was also made of metal and skinned with fabric, which was tauter than fuselage skin. This arrangement was “borrowed” from the French Dewoitine D1C1 fighter, which the Japanese acquired in 1924. The aircraft featured fixed landing gear with spats. The new fighter was to be powered by the 700 hp Mitsubishi A-4 engine and armed with two 7.7 mm Type 89 machine guns mounted on top of the engine. The machine received its official designation “Experimental Navy Fighter 7 Shi” and factory designation 1MF10.
Horikoshi and his team ran into serious difficulties designing the prototype. Although the machine was ready in February 1933, it quickly became apparent that it fell short of the expectations. In relation to the wingspan the fuselage was too long and the airframe was in need of aerodynamic refinement. Despite those obvious shortcomings, the prototype began its flight test program just a month later with Yoshitaka Kajima serving as the program’s test pilot.