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.
