Kawasaki Ki-61 Tony

Kawasaki Ki-61 Hien (Tony) Technical Data

Type:
Single-seat fighter. All-metal construction with fabric-covered control surfaces.

Accommodation:
Pilot in enclosed cockpit.

Power plant:
(Prototypes, Ki-61-I series) One Kawasaki Ha-40 twelve-cylinder inverted-vee liquid-cooled engine, rated at 1,180 for take-off and 1,180 hp at 13,780 ft.

(Ki-61-II series and Ki-61-III prototype) One Kawasaki Ha-140 twelve-cylinder inverted-vee liquid-cooled engine, rated at 1,500 hp for take-off and 1,250 hp at 18,700 ft.

Armament:
(Ki-61-Ia) Two fuselage-mounted 12.7mm machine guns and two wing-mounted 7.7mm machine guns.

(Ki-61-Ib) Four 12.7mm machine guns, two in the fuselage, two in the wings.

(388 modified Ki-61-Ias and -Ibs) Two fuselage-mounted 12.7mm machine guns and two wing mounted 20mm Mauser MG-151 cannon imported from Germany.

(Ki-61-I-KAIc, Ki-61-II, -II-KAIa, and -III prototype) Two fuselage-mounted 20mm cannon and two wing-mounted 12.7mm machine guns.

(Ki-61-I-KAId) Two fuselage-mounted 12.7mm machine guns and two wing-mounted 30mm cannon. (Ki-61-II-KAIb) Four 20mm cannon, two in the fuselage, two in the wings.

External stores:
(All except prototypes, Ki-61-Ia and -Ib) Two wing-mounted 44-gallon drop tanks, or two 551-lb bombs.

Dimensions, weights, and performance:

Ki-61-Ib:
Wingspan, 39 ft. 4 7/16 in.;
length, 28 ft. 8 ½ in.;
height, 12 ft. 1 11/16 in.;
wing area, 215.278 sq. ft.;
empty weight, 4,872 lb.;
loaded weight, 6,504 lb.;
maximum weight, 7,165 lb.;
wing loading, 30.2 lb./sq. ft.;
power loading, 5.53 lb./hp;
maximum speed, 368 mph at 15,945 ft.;
cruising speed, 249 mph at 13,125 ft.;
climb to 16,405 ft., 5 min. 31 sec.;
service ceiling, 37,730 ft.;
normal range, 373 miles;
maximum range, 684 miles.

Ki-61-I-KAIc:
Wingspan, 39 ft. 4 7/16 in.;
length, 29 ft. 4 in.;
height, 12 ft. 1 11/16 in.;
wing area, 215.278 sq. ft.;
empty weight, 5,798 lb.;
loaded weight,7,650 lb.;
maximum weight, N/A;
wing loading, 35.1 lb./sq. ft.;
power loading, 6.48 lb./hp;
maximum speed, 366 mph at 13,980 ft.;
cruising speed, 249 mph at 13,125 ft.;
climb to 16,405 ft., 7 min.;
service ceiling, 32,810 ft.;
normal range, 373 miles;
maximum range, 1,120 miles.

Ki-61-II-KAIa:
Wingspan, 39 ft. 4 7/16 in.;
length, 30 ft. 5/8 in.;
height, 12 ft. 1 11/16 in.;
wing area, 215.278 sq. ft.;
empty weight, 6,261 lb.;
loaded weight, 8,333 lb.;
maximum weight, 8,433 lb.;
wing loading, 38.8 lb./sq. ft.;
power loading, 5.56 lb./hp;
maximum speed, 379 mph at 19,685 ft.;
cruising speed, 249 mph at 13,125 ft.;
climb to 16,405 ft., 6 min.;
service ceiling, 36,090 ft.;
normal range, 684 miles;
maximum range, 995 miles.

Later Army fighter. Only Japanese fighter of the war powered by an in-line engine. Code named "Swallow." The Tony was one of the few examples of German-Japanese technical cooperation in the war. Via submarine, Germany sent blueprints and two working examples of its excellent Bf109, including the DB 601A engine. Modified for Japanese production, the Ki61 emerged, a good fighter in theory, but which always bedeviled the Japanese in their attempts to build it in numbers, build it reliably, and maintain it in the field. The JAAF deployed the Tony to Rabaul and then to New Guinea. One-on-one, a well-maintained Ki-61 Tony, with a good pilot, could threaten any U.S. fighter. But difficulties with production, maintenance, and pilot training made that the exceptional case.

A standard Ki-61-I of the 37th Training Chutai, Formosa, 1944

The Ki-61 was unique among Japanese fighters of the Second World War. It was the first JAAF fighter to incorporate from the outset the armor plating and self-sealing fuel tanks deemed indispensable by its opponents, and its liquid-cooled engine, long tapering nose, and high-aspect-ratio wings gave it a most un-Japanese look. Indeed, when first encountered over New Guinea in the summer of 1943, the Hien (Swallow) was at first thought to be a copy of the Bf-109 or of the Italian Macchi MC-202. The latter report earned for the Ki-61 the code name Tony.

During the 20s and 30s, the Kawasaki Aircraft Co. Ltd. was the leading advocate of liquid-cooled aircraft engines in Japan. The Ki-10 biplane fighter, for example, was a Kawasaki product, and was powered by a liquid-cooled V-12 engine. After Nakajima’s Ki-27 was chosen over their own Ki-28 to succeed the Ki-10, Kawasaki negotiated with Daimler-Benz for license production rights for the DB-601A series of engines (at the same time, Aichi was also seeking the rights to produce their own copy of the DB-601A for the Navy as the Atsuta). A Japanese technical team returned to Japan in April 1940 with blueprints and examples of the Daimler-Benz engine to serve as production patterns. After a little over a year’s work to adapt the DB-601A to Japanese production techniques, the first Japanese-built version, designated the Kawasaki Ha-40, was completed in July 1941. Four months later, it passed all required ground tests, and Kawasaki formally began production of the new engine for the Army.

While negotiating with Daimler-Benz, Kawasaki worked to interest the JAAF in a new fighter aircraft to be powered by this type of engine. Reports from the battle-fronts in Europe showed the apparent superiority of the liquid-cooled engine over the air-cooled radial, so the Air Staff, in February 1940, told Kawasaki to proceed with two prototypes: the Ki-60, a heavy interceptor, and the Ki-61, a lighter all-around fighter. But in December 1940, the Army instructed Kawasaki to abandon the Ki-60 and concentrate on the Ki-61.

A Ki-61-I of the Akeno Fighter Training School, 1944.

The Ki-61, designed by Takeo Doi and Shin Owada, showed the strong influence of Dr. Richard Vogt, a German engineer who had worked with Kawasaki in the 20s and early 30s, and had later become Blohm und Voss’s chief designer. To increase maneuverability and obtain a useful range, Doi and Owada chose a long-span wing of high-aspect ratio and large area. Considerable attention was also given to weight and drag reduction, yet retaining the armor plating and self-sealing fuel tanks that European combat had shown were so important to a fighter aircraft. The planned armament was to be two 12.7mm fuselage-mounted machine guns, and two wing guns of either 7.7mm or 12.7mm caliber; either way, this was double the armament of the Nakajima Ki-43 then entering service.

The first prototype flew in December 1941, even as Kawasaki was (with the JAAF’s authorization) beginning to tool up for full production. That the Army had made the right decision to do this even before the plane was first flown was shown by the success of the prototype during handling and performance tests; in particular, the Army was sanguine about the Ki-61’s top speed-367 mph at 19,685 feet. Eleven more prototypes/pre-production aircraft were built in the early part of 1942, and actual service trials began. The military pilots thought the new aircraft’s maneuverability was sluggish, having cut their teeth in planes like the Ki-43, but the majority were highly enthusiastic about the Ki-61’s high level and diving speeds, its built-in protection, and its armament. The 13th Ki-61-lucky number!-was the first true production machine, differing from the earlier planes only in minor details. In the final tests, this machine was pitted against a Ki-43, a Ki-44, an imported Bf-109, and a captured Curtiss P-40E. Although it could not win a tight-turning dogfight against the Ki-43, the Ki-61 was nonetheless judged the best overall performer, and so, at the turn of 1942-43, the JAAF formally adopted it as the Army Type 3 Fighter Model Ia (Ki-61-Ia). This first model was armed with two fuselage-mounted 12.7mm machine guns and two wing-mounted 7.7mm guns; the next version, the Ki-61-Ib, replaced the 7.7mm wing guns with weapons of 12.7mm caliber.

First deliveries of the Hien (as the plane was officially nicknamed in Japan) were made to the 23rd Independent Squadron in February 1943, this outfit serving as a pilot training and conversion unit. The first actual combat operations began just a few months later when the 68th and 78th Sentais were deployed to New Guinea. Swiftly these two fighter groups proved that the Hien was much better suited for combat against the US and Australian fighters than its stable-mate, the Ki-43. Since the Allies refused to fight the Hayabusas in dogfights and resorted instead to hit-and-run attacks that emphasized diving speed and firepower over dogfighting, the Ki-61’s faster speed, heavier armament, and better protection fostered greater aggressiveness in those JAAF pilots fortunate enough to fly Hiens. Unfortunately, the Ki-61 suffered from two grave disadvantages: first, its range was shorter than that of the Ki-43, so it was mostly confined to interception missions instead of seeking the enemy out in fighter sweeps; and second, the Ha-40 engine was proving to be alarmingly unreliable under combat conditions, especially in the tropical climate of New Guinea. But when it was actually in the air, the Hien was a fine fighter, liked by its pilots and respected by its enemies.

Good 3/4-rear shot of a Ki-61-II, shortly after VJ-Day.

The Army wanted to replace the Ki-61’s fuselage-mounted machine guns with a pair of 20mm cannon from an early stage of its development, but a domestically-produced weapon was not yet available (nearly all such weapons being earmarked for Navy use in planes like the Zero). Three hundred and eighty-eight Ki-61-Ias and -Ibs received a pair of German-made Mauser MG-151s, one in each wing. Space in the thin wing was limited, so the weapon had to be mounted on its side. A small underwing fairing covered the breech, and local strengthening was required due to the greater recoil force of the cannon compared to the original machine guns.

In addition to experimentation with the armament, Engineer Doi had a single Ki-61-I modified to test a surface-evaporation cooling system, as proposed for the experimental Ki-64. This particular Hien had its ventral radiator tub replaced with a much smaller retractable unit, solely for use on the ground. While airborne, cooling for the engine was provided by steam evaporation through wing condensers with a total area of 150.694 square feet. Thirty-five test flights were made between October 1942 and the end of 1943; a maximum speed of 391 mph was recorded, but the program was ended as it was not intended to use this system for the Ki-61, only for the Ki-64 (which was eventually abandoned).

The Hien’sengine woes and short range clearly were sources of concern, so Takeo Doi was directed to work on improving the breed. The Ki-61-I-KAIc was the next production model; this variant had a pair of Japanese-made 20mm Ho-5 cannon replacing the fuselage machine guns, the wing guns being 12.7mm weapons. The wings were strengthened to allow a faster diving speed, underwing racks were added to allow the carrying of either drop tanks or bombs, and the fuselage was slightly lengthened and the rear section made detachable. A fixed tailwheel replaced the retractable unit, while the controls were slightly modified. The -KAIc entered production in January 1944, this type finally supplanting the earlier models on Kawasaki’s production line by August of that year. Hien production had been slow up to the end of 1943, but now the tempo increased and the monthly rate reached a high of 254 planes in July 1944. A very few Ki-61-I-KAIds were also built; these had 30mm wing cannon and 12.7mm fuselage guns. Total production of these early versions of the Hien was 2,654 by January 1945.

Major Teruhiko Kobayashi (left) and his crew chief pose in front of the Major's Ki-61-I; note the impressive kill marks representing B-29s.

In addition to its original operational zones in New Guinea and Rabaul, the Ki-61-I and -I-KAI flew and fought over the Philippines, China, Formosa, Okinawa, and over the home islands of Japan itself. In the latter, it was heavily engaged against the B-29 Superfortress; although it generally lacked the high-altitude performance needed to pursue and destroy the B-29, several pilots claimed impressive scores against the huge American bombers. Major Teruhiko Kobayashi, for instance, the commander of the 244th Sentai, claimed a total of no less than ten B-29s destroyed, at least one by ramming. He openly displayed his score in little silhouettes, painted along the fuselage of his Ki-61-I-KAIc; he’s known to have flown at least four such planes. Most of them were painted with a green blotchy camouflage over natural metal, but one was overall green over natural metal undersurfaces. The home-based Ki-61s also intercepted US naval aircraft, and fights against the Corsairs and Hellcats were furious, but the Hien was not really outclassed until the advent of the excellent P-51D Mustang.

Shortly after the Ha-40 engine commenced production at the Akashi engine factory, the Kawasaki engineers commenced development of a more powerful and higher-altitude-rated version, the 1,500 hp Ha-140. The Army Air Staff was very eager to see this engine in a specially designed variant of the Hien, so Kawasaki created the Ki-61-II. First flying in December 1943, the Ki-61-II had an enlarged wing and a redesigned aft canopy to improve pilot visibility. But the Ha-140 engine proved disappointingly unreliable, the crankshaft in particular being weak and prone to breakage. And the enlarged wings also proved to be troublesome, sometimes failing while under maneuverability tests. Thus, only eight Ki-61-IIs were actually built, and the ninth airframe was made the prototype for the Ki-61-II-KAI. This variant reverted to the earlier wing but featured a slightly lengthened fuselage. The airframe problems were eradicated, but the engine still gave problems. When it was operating properly, the Ki-61-II-KAI was quite fast (379 mph) and climbed well (attaining 16,405 ft. in six minutes flat). The Army was confident that the engine teething troubles could eventually be eradicated, so they gave their blessing for production to begin. But the Army’s confidence proved to be misplaced.

The Ki-61-II-KAI entered production in September 1944, in two versions: the -KAIa had an armament of two fuselage-mounted 20mm cannon and two wing-mounted 12.7mm machine guns, and the -KAIb had four cannon, two in the fuselage, two in the wings. But the Ki-61-II-KAI never replaced the earlier -I-KAI either in production or in operational units, because the engine was just too unreliable. When the engine ran correctly, the Ki-61-II-KAI was an excellent interceptor, being the only JAAF fighter capable of maintaining formation at the B-29’s best altitude, but the lack of skilled workers and well-trained Army ground crews meant that the Ha-140 engine rarely gave its full rated power or performed well in the air. The final crippling blow fell on January 19, 1945, when the Akashi engine plant was totally destroyed by a B-29 raid. Only 374 Ki-61-II-KAIs were built; about thirty were destroyed on the ground while awaiting delivery to combat units, and no less than 275 were left waiting for engines after the Akashi plant was wiped out. Just before this disaster, one prototype of the Ki-61-III was built and flown; this version differed from the -II solely by the addition of an all-around-vision canopy. Counting all versions of the Ki-61, total production was 3,078.

Plagued as it was by production difficulties and unsolvable engine troubles, the Ki-61 Hien was never as widely used as its Nakajima competitors. Still, during the mid-war years, it was the only Army fighter capable of meeting Allied fighters on anything like an equal basis. By combining reasonably good maneuverability with a strong structure and good pilot and fuel protection, it pointed the way to what could’ve been the JAAF’s future. It also gave birth to the superb Ki-100 … but that’s another story.

 

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