Mitsubishi Ki-46

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The Mitsubishi Ki-46 (Allied codename: “Dinah”) was a twin-engine Japanese reconnaissance plane that served throughout World War II in China and the Pacific.

History

In 1937, the Japanese Imperial Army Air Headquarters submitted specifications for the replacement to the Mitsubishi Ki-15 reconnaissance plane then entering service. The new aircraft would have to be fast (373 mph, much faster than any Japanese aircraft of the time) and have an endurance of six hours at 250 mph. Mitsubishi was already working on a twin-engine replacement for the Ki-15, and was awarded the contract in December 1937.

However, Mitsubishi engineers quickly realized that their design would not meet the Army’s needs, and discarded it in favor of a more streamlined model. The new plane was designated the Ki-46, and flight trials began in November 1939. Although its maximum speed was only 335 mph, 40 mph slower than the requirement, the Army was happy enough with it, and ordered it into production.

Design

The Dinah had two Mitsubishi engines of 900 hp apiece. It carried a crew of two, a pilot and a radio operator. The crew compartment was divided in two by a bay containing cameras and a large fuel tank. This unusual arrangement was dictated by the desire to put the fuel tank at the center of the plane’s gravity. Every effort was made to make the Ki-46 as streamlined as possible.

Variants

As previously mentioned, the first variant, the Ki-46-I, was slower than desired, prompting the makers to add a rear-firing machine gun, operated by the radio operator, for defense. Production of the new plane was also slow at first. Not only was it relatively hard to manufacture, Mitsubishi was committed to producing other aircraft for the Japanese armed forces as well, including the A6M Zero fighter and the G4M bomber. In spring of 1941, only four Ki-46s were coming off the production line every month, although Mitsubishi took measures to speed up production soon after that.

Although the Army accepted the Ki-46-I, they specified that Mitsubishi would immediately start work on a faster version, leading to the Ki-46-II. The design remained the same, but the engines were replaced with newer units that had greater horsepower (1080 hp) and a supercharger for high altitude performance. The new variant had a top speed of 375 mph, two miles an hour faster than the Army had specified and faster than almost every Allied plane at the beginning of the Pacific War. The Ki-46-II went into production in early 1941, and the Army had enough planes for multiple operational reconnaissance squadrons by late 1941. This was the most common version of the Dinah, with almost 1100 examples produced in total.

The Japanese Army knew that Dinah’s speed advantage wouldn’t last as the Allies produced faster fighters, so the Mitsubishi designers were put to work on making the plane even faster, and giving it greater endurance. The Ki-46-III first flew in December 1942. It had more powerful engines (1250 hp) with fuel injection, resulting in a top speed of 391 mph, and range was greatly improved by adding more fuel capacity. The airframe was also re-designed by making the canopy continuous and smooth with the nose, giving the Dinah a very elegant appearance. The rear gun was removed, as well, and the landing gear were made stronger (weak landing gear had proved to be a problem with the Ki-46-II).

Later in the war, when the Japanese Empire was increasingly on the defensive, some Ki-46-IIIs were converted into light attack planes or interceptors, with two 20 mm cannons in the nose.

Another variant, the Ki-46-IV, was designed, and it first flew in February 1944. The plane had greater range, and an improved rate of climb, but manufacture of the engines proved troublesome, and only four copies were produced.

Service

The Ki-46 was first used on missions over China, but was later used to scout out British, Dutch, and American bases in preparation for the December 1941 offensive. Once the Dutch East Indies had been taken, Dinahs operating from the island of Timor could cover most of northern Australia, and Burma-based Dinahs kept tabs on British naval activities at Ceylon.

In the first year of the war, the speedy Dinah was practically invulnerable, and could still operate with a certain degree of impunity after the introduction of advanced Allied fighters like the P-38 Lightning and F6F Hellcat. Even in 1945, when the Allies had achieved almost complete air superiority, it was able to operate over heavily defended bases with a fair chance of survival. It was mainly because of this survivability that the Dinah was very popular with its crews.

Attack Dinahs

The Dinahs that had been converted into interceptors proved to be a disappointment. While their speed was greater than other Japanese fighters, their relatively low rate of climb meant that they very often couldn’t intercept the high-flying B-29s in time. Even when they did manage to intercept, their lack of any protection made them vulnerable to the bombers’ heavy defensive fire. When the B-29s switched to night bombing, the radarless Ki-46s were rendered almost useless.

The Dinahs modified for ground attack had a little more success (see: The Achilles), but their lack of protection was a problem on these missions as well.

Survivors

One Dinah, a Ki-46-III, survived to the present day and is currently on display in the Cosford Aviation Museum in England.

Sources