It was only after more modern Allied fighters appeared that the Ki-43 design was addressed once more. This time, Nakajima saw fit to add the all-important self-sealing fuel tanks as well as armor near the cockpit - two standard design features to be found on Allied warplanes. A more powerful engine was also eventually added to help increase the lethality of the Ki-43 series and the wings were now noticeably clipped. All these changes went on to produce the much improved Ki-43-II series in the family line.
The Ki-43-IIa sported provisions for the carrying of 2 x 551lb bombs under the wings. The Ki-43-IIb had radio equipment installed in the cockpit and was powered by a Nakajima Ha-115 14-cylinder, air-cooled radial piston engine delivering 1,150 horsepower. This supplied the airframe with a top speed of 329 miles per hour (cruise speed = 273mph), a range of 1,095 miles and a service ceiling of 36,750 feet. The Ki-43-KAI was given ejector exhaust stacks.
The final important mark became the Ki-43-III series. Prototypes were given the Nakajima Ha-115-II series engine of 1,230 horsepower and increased their operational range by the addition of 2 x 45 gallon drop tanks. The Ki-43-IIIa was the main production mark and was followed by the Ki-43-IIIb that was armed with 20mm cannons over the original machine gun suite.
One other notable Ki-43 variant became the Ki-62 "Project" which was nothing more than a highly modified Ki-43 for the dedicated interceptor role. This version sported and even more powerful engine and could be armed with either 30mm or 40mm cannons as required.
The Ki-43 proved her worth throughout all of World War 2. After her service in the active Pacific Theater was limited to the area around the Japanese islands, the aircraft was utilized as an interceptor for homeland defense, particularly of the national capital of Tokyo. Some Ki-43 airframes were also set aside for use in the lethal, yet suicidal, kamikaze runs against Allied ships in the Pacific.
In all, some 5,919 examples of Ki-43 Hayabusa fighters were produced from 1942 to 1945, making her the most-produced IJA fighter and following only the Mitsubishi A6M "Zero" in terms of overall production. The type was officially retired from Japanese service in 1945 with the end of the war but soldiered on in the Chinese inventory (post-war) up until 1952. Other wartime operators included Manchukuo and Thailand with additional post-war operators being France, Indonesia and North Korea. The French utilized Ki-43 models in the Indochina War against Viet Minh rebel elements - though these were captured examples painted in the colors of the French Air Force and used primarily in the ground attack role. Similarly, the North Korean Hayabusas were also captured post-war remnants as were the Indonesian mounts - the latter against Dutch forces in an effort to end colonial rule.
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