The Ki-30 was a type of airplane — a single-engined, multi-seat land-based light bomber – that was steadily becoming obsolete by the beginning of World War II. It was the first Japanese aircraft of its kind that was fitted with a double-row air-cooled radial engine, split flaps, an internal bomb-bay, and a variable-pitch propeller, but it was fated to spend most of its operational career toiling in the obscurity of China, at a time when almost no aerial opposition faced Japan’s Imperial Army Air Force. However, though it was never famous, the Ann, as it was code-named by the Western Allies, was notably easy to fly and maintain and possessed hardly any vices, for which its flight and ground crews regarded it with affection.

An in-flight shot of one of the prototypes or service-test Ki-30s during a test flight (note the two men in the rear-seat position!).

During the mid-1930s the Japanese Army began implementing an ambitious modernizing and expansion program based around aircraft wholly designed and built by Japan itself. From this program sprang the Nakajima Ki-27 fighter, the Mitsubishi Ki-21 "heavy" bomber, and the Mitsubishi Ki-15 reconnaissance plane. The Army also wanted a suitable replacement for the Kawasaki Ki-3 then equipping its light bomber units, so in May 1936 the Army Air Staff (Koku Hombu) asked the Mitsubishi and Kawasaki companies to build two prototype light bombers apiece by December of the same year. The requirements set out by the specification included the following: (a) a top speed of 248.5 mph at 9,845 feet; (b) a normal operating altitude of between 6,560 feet and 13,125 feet; (c) the ability to climb to 9,845 feet in 8 minutes exact; (d) engine to be one of the following – the 825-hp Mitsubishi Ha-6 radial, 850-hp Nakajima Ha-5 radial, or 850-hp Kawasaki Ha-9-IIb liquid-cooled inline engine; (e) a normal bombload of 661 lbs. and a maximum of 992 lbs.; (f) defensive armament of one forward-firing machine gun and one flexible rearward-firing machine gun; (g) the ability to perform 60-degree dives for glide-bombing; and (h) a loaded weight not to exceed 7,275 lbs. Colonel Komamura of the JAAF was to supervise the Mitsubishi design team — engineers Kawano, Mizumo, and Ohki.

Preparing for a mission, somewhere in China.

Originally, the new aircraft was to have had a retractable main undercarriage, but wind-tunnel tests with models indicated that the gain in speed would be offset greatly by a retractable landing gear’s extra weight and complexity. As a consequence, a sturdy fixed gear with “spatted" main wheels was chosen instead. The wing was mounted at a point above the line of the aircraft's belly in order to give the prototype a fully enclosed bomb bay within the fuselage. The pilot sat just above the leading edge of the wing, and the rear-gunner/radio-operator just behind the wing trailing edge, in a long, extensively-framed “greenhouse" canopy which gave both crewmen excellent all-around vision. Oddly, there was no onboard intercom radio; the pilot and gunner communicated using a primitive “gosport tube" instead. The Ha-6 engine was chosen, driving a three-bladed variable-pitch propeller (this kind of propeller was retained throughout the aircraft’s service lifetime), and the first prototype took off on its maiden flight on February 28, 1937, from Kagamigahara airfield. A second prototype, differing from the first solely in being powered by the Nakajima Ha-5 engine, was completed during the same month. Although they were slightly behind schedule and were somewhat overweight, the two prototypes met or exceeded every other requirement. The second prototype’s top speed of 263 mph at 13,125 feet so impressed the Army that the Ha-5 engine powered the Ki-30 throughout its service life. Compared to its rival, the Kawasaki Ki-32, it was more reliable, simpler to maintain, and could also sustain more battle damage and continue flying, all largely due to its having an air-cooled radial engine and not a liquid-cooled vee type.

A fully-loaded Ki-30 over China, late 1930s.

Sixteen service test examples were completed by January of 1938, all of these being powered by the Ha-5-KAI radial. Only two other changes were made – the forward-firing 7.7mm machine gun was moved from the left main undercarriage leg to within the left wing, and the outboard main wheel covers were removed to ease operations from muddy, unpaved forward airfields. Once these first sixteen planes were built and tested, the new aircraft was placed into production as the Army Type 97 Light Bomber (Ki-30) in March 1938. The parent company built 618 production machines through April 1940, and the First Army Air Arsenal at Tachikawa built 68 more by the time production ceased in September 1941. Including prototypes and service-test types, a grand total of 704 Ki-30s were built.

The Ki-30 swiftly built up a reputation as one of the JAAF’s most reliable machines once it was committed to combat over China in the spring of 1938. Losses were low as it nearly always operated within the range of escorting Ki-27 fighters. When the Pacific War begin in December 1941, the Ann was committed to operations in the Philippines once Japan gained local aerial superiority, but it quickly became clear that the Ki-30 was no match for modern Allied fighters. By the end of 1942, the Ann was relegated to training, and others were transferred to the Royal Thai Air Force, which had already used the Ki-30 as early as January 1941, against the French in Indochina. And in 1945, along with other obsolete aircraft, the Ki-30 was used as a suicide attack plane as Japan desperately tried to stave off defeat.

Bombs away! Two Ki-30s release their lethal loads over China.

Mitsubishi Ki-30 (Ann) Technical Data