Modern-Aviation

Since May of 1937, the Empire of Japan - both the Imperial Japanese Army Air Force and the Imperial Japanese Navy Air Service branches - relied on the Mitsubishi Ki-15 aircraft for light bombing and reconnaissance sorties. The aircraft featured an enclosed cockpit for two, a low monoplane wing assembly and spatted main landing gear legs, the latter in a permanently fixed positions. About 500 of these aircraft stocked Japanese inventories and only a few developed variants existed. In December of 1937, a new requirement came down from the Japanese air force for a long-range, fast reconnaissance platform to succeed the outgoing Ki-15.

The Mitsubishi concern returned with an all-new design that held some basic similarities to the Ki-15 in that it used two crew and held low-set monoplane wings. The new aircraft sported a well rounded fuselage with each wing fitting a streamlined engine nacelle powering three-bladed propellers. The fuselage design tapered off into the empennage which was capped by a single - rather cropped - vertical tail fin with applicable tailplanes. The crewed would sit in two segregated cockpits - the pilot in a forward compartment and the observer/rear gunner in a rear compartment ahead of the tail. To fulfill the long-range requirement, fuel was stored in multiple locations about the design including a large storage tank fitted between the forward and aft cockpits. Mitsubishi-brand radial piston engines were fitted into specially-designed streamlined nacelles that complimented the aerodynamic qualities of the aircraft. Armament consisted of only a single self-defense Type 89 machine gun set in a rear-firing position to help protect the aircraft's vulnerable "six". Construction of a prototype ensued and produced the "Ki-46" designation.

First flight of the Ki-46 was recorded on November of 1939 which proved her engines lacked the required output power and overall speed envisioned by the IJAAF. Worked continued on the type and a new Mitsubishi powerplant (Ha.26-I radial of 900 horsepower) was fitted while the IJAAF - satisfied with the aircraft's short-term outlook - ordered serial production of the Ki-46. The newer Ki-46-I reconnaissance version was introduced in July of 1941 and immediately made its mark in service to the IJAAF. 34 examples of this type were completed before manufacture switched to the definitive Ki-46-II refined production form of which 1,093 examples were completed.

The Ki-46 was designed to replace the Mitsubishi Ki-15 'Babs', a reconnaissance aircraft that entered service in May 1937. Although the Ki-15 was a successful design it was already clear that it was not fast enough to elude the new generation of monoplane fighters, and so in 1937 officers from the Technical Branch of the Koku Hombu (Japanese Air Army HQ) began work on a specification for a replacement. Tomio Kubo, the cheif designer of the Ki-46 designed a cantilever low-wing monoplane with retractable tailwheel landing gear, powered by two 671kW Mitsubishi Ha-21-l radial engines, the two-seat Ki-46 prototype was flown for the first time in late November 1939. Early testing showed that maximum speed of the Ki-46 was some 10% below specification, but as its speed and overall performance was better than in-service army and navy aircraft the type was ordered into production.

First combat operations for the Ki-46 saw her acting over both Manchukuo and China before branching out further into the Pacific. Within time, the aircraft proved a regular sight in the skies across other territories for, from the outset, the Ki-46 was an excellent performing aircraft highly suitable for the fast, high-level reconnaissance role originally envisioned. Its inherent speed made her virtually immune to ground-based fire and assault from enemy interceptors. Such dominance allowed a certain feeling of superiority for the IJAAF and this was used to a grand advantage for as long as this dominance lasted. The Ki-46 would go on to become one of the best reconnaissance aircraft of the war.

However, Japanese authorities were not blind to advancements being made on the Allied side. Basic fighter designs were all being put through new paces and completed with evermore improved performance specifications themselves. To stay ahead of the curve, the IJAAF charged Mitsubishi with evolving the Ki-46-II into an improved form through the installation of more capable engines. Mitsubishi engineers also took to refining key aerodynamic features of the airframe including the nose - now sporting a smoother, all-glazed look. The modified version first took to the air in December of 1942 and proved faster than the first incarnation. The aircraft was adopted as the Ki-46-III and 613 examples were delivered.

The improved Ki-46-ll had 805kW Mitsubishi Ha-102 engines, this powerplant giving a maximum speed slightly in excess of the original specification.was the major production version, with more than 1,000 built. A number of were converted later into three-seat radio/navigation trainers under the designation Ki-46-ll KAI. Due to unacceptably high losses of Ki-46-IIs, newer variants included the faster and improved Ki-46-III of which 609 were built. The Ki-46-III was given a more powerful engine and a revised canopy. Gone was the ‘traditional’ stepped windshield and instead a smooth, curved, glazed panel extended over the pilot’s seat (the only piece of armor plate in the whole aircraft), and gave the ‘Dinah’ an aerodynamic nose. The faulty undercarriage was strengthened to carry the hefty fuel load (up from 367 to 417 imperial gallons). The whole fuel system was redesigned, with 5 unprotected tanks in each wing (included new leading edge tanks) and two enormous black rubber ‘bag’ tanks, one between the pilot and the observer, and the other directly in front of the pilot’s cockpit. It entered service during 1943 with a small number were converted later as Ki-46-lll KAI fighter interceptors and the Ki-46lllb ground-attack aircraft that was developed in March 1945. It was armed with two 20mm cannon, and entered service in small numbers as the Army Type 100 Assault Plane.

Production of all versions totalled 1,742, all built by Mitsubishi.

By the end of the war in 1945, a desperate Japanese defensive campaign saw the ki-46 series converted into an ad hoc heavily-armed interceptor platform. The main threat to the Japanese mainland now came from the high-altitude Boeing B-29 Superfortress which could essentially act with its own level of impunity over Japanese defenses and out of reach of enemy interceptors. As a bomber interceptor, armament of the Ki-46 was upgraded to include 2 x 20mm cannons in the nose and 1 x 37mm cannon in an oblique firing position. The latter armament was intended to engage bombers from the rear and underneath - the most vulnerable area of an enemy bomber when in flight. These versions (Ki-46-III-KAI) proved adequate for the role conversion but were not as successful as anticipated. The airframe was simply not designed for the sustained firing of the large-caliber 37mm cannon, especially in its semi-vertical fitting, and the aircraft had trouble reaching its defined interception altitudes within time. Even when it did reach B-29 bombers, the aircraft lacked any armor protection or self-sealing fuel tanks and essentially made for target fodder against B-29 gunners. The Ki-46-III-KAI appeared in October of 1944 and was in operational service by the following month. When the American aircrews converted over the night operations, the tactical usefulness of the Ki-46-III interceptor was even less for they were never adapted to the night fighter role with radar or similar tracking facilities. The Ki-46-IIIb was a similar III-series mark though developed specifically for the ground attack role and produced sans the oblique-firing 37mm cannon. Several other experimental forms existed to test out engines but these came to naught while still others never materialized from the drawing boards.

The Ki-46 was officially retired in 1945 after the Japanese Empire fell to the Allies. Two were operated by the Chinese after the war for a short time after but their recorded use ended by the mid-1950s.

The formal name of the Ki-46 was "Type 100 Command Reconnaissance Aircraft" and she was known to Allied forces by the codename of "Dinah".