Japanese Light Bombers [1] in China

Arriving at Po-yun air base, Kuangtung, Southern China, in June, 1941, newly commissioned 2nd Lt Haruo Matsuura reported to the Sentai Commander, Lt Col Hajime Sakurai, at the Headquarters of 27th Sentai. The commander assigned Haruo to 3rd Chutai (Company), company commander of which was Capt Rokuro Seto. The 27th Sentai was originally established in Manchukuo in 1937, equipped with type 97 light bomber (Ki-30), and then type 98 light bomber (Ki-32). When Haruo arrived, the Sentai was in the process of moving its base to Tien-he airfield, which was also in Kuangtung area, and their equipment had already been changed to type 99 ground assault plane (Ki-51), much better in performance compared those two predecessors.

Ki-15 (Mitsubishi) “Karigane” (“Wild Goose”): originally developed as a private venture by Mitsubishi, with the sponsorship of Asahi Shimbun, one of the leading Japanese newspapers. Under this sponsorship the second prototype, registered to the newspaper and given the name “Kamikaze” (“Divine Wind”), in August 1937 garnered great publicity with record-setting flight from Japan to London, covering 9,900 miles in 51 hours 17 minutes. When war with China broke out just three months later, the variant under development for the Army (who had come to show interest at an early stage) was ready for action, and was one of the first Japanese bombers to be employed in the “China Incident.” The Ki-15 was a single-engined, two-seat monoplane with fixed landing gear. In its original version it carried a single 551-lb bomb at a top speed of 280 mph. An improved variant (Ki-15-II) could accommodate 1,100 lbs of bombs at speeds of close to 300 mph. In any event, the Ki-15 was originally faster than any plane possessed by the Chinese, except for the Soviet-built I-16 fighter, which it roughly matched in speed. Armament was one 7.7mm machinegun flexibly-mounted in the rear of the cockpit, and sometimes an additional 7.7mm mg fixed to fire forward. The bomb load was carried externally. The aircraft was also used in China for photo reconnaissance. A total of over 400 were built for the Army, and from 1939 the Navy received 50 of their own reconnaissance variant, the C5M (capable of just over 300 mph). One of the latter made the first sighting of the PRINCE OF WALES and REPULSE off the coast of Malaya, setting in motion the chain of events leading to their eventual sinking by Japanese Navy air units. But by the time of Pearl Harbor the Army Ki-15 was well into the process of being phased out, as its replacements had started entering service at the end of 1938, and its service was mainly limited to the China theatre.

Ki-30 (Mitsubishi): the Japanese Army undertook a comprehensive modernization plan for its air units in 1935. This program produced four basic combat types, the Ki-27 fighter, the Ki-21 heavy bomber, and the Ki-30 and Ki-32 light bombers. The Ki-30 was a single-engined, two-seat monoplane, with fixed landing gear. Like most of the new Army aircraft, it was an all-metal design, with stressed-skin construction. The Ki-30 had an internal bomb bay holding three 220-lb bombs. Armament consisted of one or two 7.7mm mgs fixed to fire forward, and one 7.7mm hand-aimed from the rear of the cockpit. Top speed was just over 260 mph. Entering service at the end of 1938, and rushed almost immediately into action over China (where it played a significant part in Japanese Army air efforts over the next three years, and, benefitting from fighter escort and scant opposition, suffered acceptably low losses), the Ki-30 was still one of the Army’s chief light bombers at the time of Pearl Harbor and throughout the great opening offensive in the Pacific and southeast Asia. It was however rather rapidly withdrawn from service in mid-1942, once these grand opening moves were successfully completed. Over 700 were built.

Ki-32 (Kawasaki): developed in competition with the Mitsubishi design that became the Ki-30, the Ki-32 was rather unusual among Japanese aircraft of the period in that it used a liquid-cooled, in-line engine instead of the radials which were preferred by most of the Japanese aircraft industry at the time. Like the Ki-30, it was a two-seat, single-engine plane, with fixed landing gear. Mounting two 7.7mm machineguns, the Ki-32 achieved a top speed of just over 260 mph while carrying up to 992 lbs of bombs. Its range was even shorter than that of the Ki-30, but what caused the most problems was engine reliability. Questions about the Ki-32’s power plant caused the Army to initially select the Ki-30 in preference to the Kawasaki design, as the radial engine was generally considered less troublesome and easier to service. However, the opening of the war with China caused the Ki-32 to be ordered into production as well. As with the Ki-30, the first examples were delivered in late 1938, and the type saw considerable service in China. Like the Ki-30, it remained in front-line use through the early months of 1942, and then was withdrawn to training duties. Although it was considered something of a second-line aircraft compared to the Ki-30, it was actually built in somewhat larger numbers, with over 850 manufactured before production ended in 1941.

Ki-48 (Kawasaki): by 1940-41 the limitations of the early Japanese Army designs of single-engined light bombers had been fully realized, and new aircraft were entering production to replace them. The early light bombers all suffered from deficiencies in range, payload, and survivability against newer fighter types, and new designs focused on improving one or more of these categories. The Ki-48 was a two-engined plane with a four-man crew. Its design and production were a direct result of the introduction of the Soviet SB-2 bomber into Chinese service—the Japanese realized that the speed of this new aircraft made it (in 1938 terms) almost immune to interception, and wished to develop something similar for their own forces. When the Ki-48 first entered service in China in 1940, it seemed to meet these standards, as, with a top speed of almost 300 mph, the opposing fighters in that theatre simply could not catch it. The Ki-48 also brought an increase in range of some 500 miles over the earlier Ki-30 and Ki-32, although its bomb load remained small— normally only 660 lbs (carried internally), although 882 lbs could be carried. Defensive armament was also still somewhat deficient, with three hand-aimed 7.7mm machineguns in the glass nose and rear-facing ventral and dorsal positions. With the first aircraft delivered in the summer of 1940, more than 550 of the original version Ki-48-I were built by June 1942, when it was replaced by the improved Ki-48-II. This had better engines, increasing speed to almost 315 mph, and also featured increased armor protection for the crew positions and fuel tanks. Later versions (beginning in 1943, mainly the Ki-48-IIc) added a second nose gun in a twin mount, and a heavy 12.7mm mg replacing the 7.7mm in the glassed-in position on top of the fuselage. These changes were still not enough to stop the aircraft from being relatively easy meat to the Allied fighters it encountered by 1942-43 over the south Pacific and Burma, and the relatively light bomb load remained a further problem. By late 1942 the Ki-48 was being increasingly relegated to night missions only in an attempt to improve its ability to survive (as for instance over Guadalcanal, where single nocturnal intruders on nuisance raids were such a common feature as to gather colourful nicknames from the Marines whose sleep they regularly disturbed). Nonetheless, the Ki-48 remained in production until 1944, for sheer lack of anything better to replace it with, and eventually over 1,950 were produced, mainly of the Ki-48-II variants.

Ki-51 (Mitsubishi): a different approach to improving the effectiveness of the Japanese Army light bombers was the development of a purpose-built dive bomber. To the disadvantage of light payloads in the Ki-30 and Ki-32 was added the problematic accuracy of level-bombing techniques, even from relatively low altitudes. The Japanese Army aircraft in China had already adopted glide-bombing techniques in an attempt to improve their ratio of hits (this was also demonstrated by a group of Ki-30’s in one of the earliest air raids on Corregidor in the Philippines). But this approach often left the attacking aircraft increasingly vulnerable to ground fire, and the often marginal improvements in bombing accuracy hardly justified the risk. The Ki-51 was therefore constructed with survivability as primary consideration. It was both highly manoeuvrable and fairly well-protected, and even when seemingly outmatched as the war progressed showed a surprising ability to elude enemy fighters. As a further bonus, the Ki-51 was designed with a short take-off and landing capability which allowed it to operate easily from crude front-line airstrips. It was in many ways an ideal ground-support plane, and the Army used it widely for most of World War II despite its deficiencies. Chief among those deficiencies was the extremely limited payload—only 440 lbs of bombs, carried externally under the wings. The Ki-51 was a single-engined two-seater, with fixed landing gear, in some respects based closely on the Ki-30 it was designed to replace. Armament consisted of two fixed 7.7mm mgs in the wings, and a third on a flexible mount in the rear of the cockpit (later in the war the rear mg was upgraded to 12.7mm calibre). Top speed was just over 260 mph. Like all the other Japanese light bombers discussed, the Ki-51 first entered service against China (in 1940). The Army relied so heavily on this plane in the close support role that in 1944 production was actually increased, and the plane was still being manufactured in 1945, a total of 2,385 being built. A few were also used for reconnaissance duties. The improved Ki-71, with retractable landing gear and a more powerful engine, was intended as a replacement, but proved only a modest improvement and never preceded beyond the prototype stage.

[1]The Japanese did not develop a dedicated single-engined ground support aircraft; the Japanese army relied on light bombers, such as the Ki-30 ('Ann'), Ki-32 ('Mary'), Ki-36 ('Ida') and Ki-51 ('Sonia'). These were all obsolescent. However, the Kawasaki Ki-45-KAI Toryu ('Nick'), although primarily designed as a twin-engined long-range fighter, turned out to be a quite useful attack aircraft. The Ki-45-KAIb version was armed with a 37 mm Type 98 tank gun, which fired the same ammunition as the Type 94 anti-tank gun (not to be confused with the less powerful Type 94 tank gun). The Type 98 was manually loaded. The Ki-45-KAIc instead carried a 37 mm Ho-203, less powerful than the Type 98 but equipped with a 15-round belt feed. The Ho-203 was later scaled up to the Ho-401 57 mm cannon, and this weapon (with 17 rounds) was installed in the attack version of the Ki-102 ('Randy') fighter, the successor of the Ki-45. Of this Ki-102b (also known as the Army Type 4 Assault Aircraft) about 200 seem to have been completed. The Ho-401 with its 520 m/s muzzle velocity was a suitable weapon for use against soft targets, but not much use against armour. Rikugun, the army aeronautical research institute, designed the Ki-93 with the Ho-402 in a belly fairing; this was also a 57 mm weapon but much larger and more powerful, firing its projectiles at 700 m/s. However, only one Ki-93 was ever flown. These Japanese aircraft were no longer as unprotected as most Japanese combat aircraft had been at the start of the conflict, but they were not heavily armoured either, the designers' priorities being performance and handling.