The Kawasaki Ki-32 ("Mary") light bomber was one of the rare inline piston-engined aircraft entries designed, manufactured, and fielded in number by the Empire of Japan during World War 2 (1939-1945). Air-cooled radial piston types were largely relied upon by way of many aircraft designs largely due to the fact that Japanese aero-industry lacked the knowhow and experience in realizing a reliable, powerful inline solution (as the Germans did with the DB600 series). As such, the Ki-32 was completed with the in-house Kawasaki Ha-9 liquid-cooled powerplant which gave the design good performance for the early war years - despite nagging reliability issues.
The Ki-31 was born through an Imperial Japanese Army (IJA) initiative calling for an all-modern, single-engine, twin-gunned monoplane fighter able to carry a 992lb bombload while maintaining speeds between 185 and 250 miles-per-hour while flying at an altitude between 6,550 and 13,000 feet - in essence an attack platform with fighter-like performance.
The call fell to both Kawasaki and its competitor, Mitsubishi, and both concerns pushed their respective designs to the service in subsequent months. The Kawasaki form utilized its inline engine to set it apart from the Mitsubishi offering - which was powered by an air-cooled Nakajima radial unit - though both followed the same form-and-function in terms of general arrangement. From this work spawned eight prototypes completed by Kawasaki which began to showcase cooling and tuning issues with the inline engine - leading the Army to select the Mitsubishi aircraft under the designation of "Ki-30".
The Kawasaki light bomber was suspended for the interim.
As a dedicated light bomber, the Ki-32 followed combat concepts developed by global players throughout the late-Interwar years and was, therefore, highly conventional in its arrangement. The engine was set in the nose section in the usual way with the two man crew seated in tandem just aft of the installation. The crew compartment was shared and covered over by a greenhouse-style canopy over midships. The fuselage was aerodynamically refined for the most part, tapering elegantly at the empennage which was capped by a rounded rudder fin with low-mounted horizontal planes. The mainplane wing members were positioned ahead of midships and given tapering from root to tip. The tips were rounded off. Like other 1930s developments, the Ki-32 had a fixed "tail-dragger" undercarriage with the main legs under center mass being spatted for some inherent aerodynamic efficiency.
The engine of choice became the Kawasaki Ha-9-IIb V12 inline outputting at 850 horsepower and driving a three-bladed propeller unit at the nose. Performance included a maximum speed of 265 miles-per-hour with a cruising speed near 185 mph, a service range out to 1,220 miles, a service ceiling up to 29,265 feet, and a rate-of-climb of 1,500 feet-per-minute.
Standard armament included a single 7.7mm machine gun in a fixed, forward-firing installation partnered with a 7.7mm machine gun on a trainable mounting in the rear cockpit. Beyond this was a modest bomb carrying capability totaling no more than 992lb of conventional drop ordnance (held internally). With this arrangement, the aircraft could dive bomb ground targets or strafe with equal lethality - it also retained a limited capability to engage intercepting enemy aircraft.
On the whole, the design held much in common with contemporaries in the Aichi D3A1, Mitsubishi Ki-30, Mitsubishi Ki-51, and Fairey Battle.
Despite the selection of the Mitsubishi design, the fate of the Ki-32 changed when the IJA found itself in need of warplanes during the late 1930s and moved to resurrect the Kawasaki light bomber - indeed the Ki-32 went on to outpace the rival Ki-30 in terms of production quantity. Following service approval, the Ki-31 entered serial production which spanned from 1938 until May of 1940 and this resulted in a total of 854 aircraft being built. The series was quickly baptized during the bloody Sino-Japanese War (1937-1945) and proved serviceable enough until technology gains overtook it by 1942 - at which time the series was relegated to training and other second-line roles. Comparatively, 704 Ki-30 attackers were produced into September of 1941.
The reliability issues inherent in the inline engine was never truly ironed out and forced a Japanese continuation with reliance on air-cooled radial powerplants for the foreseeable future.
The Ki-32 served no fewer than seven Imperial Japanese Army Air Force (IJAAF) squadrons for its time in the air and also went on to see operational service with the Manchukuo Air Force and, in 1945, with Indonesia (captured specimens). In the latter, many were lost in the Indonesian National Revolution of 1945-1949.
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