Army single-seat fighter

Infolge des vollständigen Fehlens von Jagdflugzeugen mit Reihen- bzw. V-Motoren bei der japanischen Luftwaffe und bedingt durch die zahlreichen erstmals angetroffenen Stückzahlen wurde zunächst angenommen, dass der Ki 61 (Tony) Jäger eine Lizenzbauversion der Messerschmitt Bf 109 war. Beutemaschinen ließen erkennen, dass diese Annahme irrig war, obwohl der Ha 40 Motor, mit dem die Hien angetrieben wurde, eine Leichtbauversion des deutschen DB 601 Motors darstellte, und das Jagdflugzeug anfangs in großem Ausmaß die Bordkanone Mauser MG 151 benutzte.

Das unter dem Codenamen ‚Tony‘ bekannte einsitzige Jagdflugzeug Kawasaki Hien (Schwalbe) wurde ab April 1943 von der Kaiserlich-Japanischen Armee im 2. Weltkrieg eingesetzt und erwies sich als gefährliche Waffe gegen die alliierten Kampfflugzeuge. Mit einem 1175 PS starke Triebwerk konnte eine Höchstgeschwindigkeit von 560 km/h erreicht werden.
Dienstgipfelhöhe 10000m




Kawasaki Ki-61 Hien'Tony'
Ki-61-IIb Hien in the markings ot the 244th. Sentai 2nd Chutai (Tokyo Defence Area, 1945)

In 1937 Kawasaki purchased a licence to build the German DB.601 engine - the resulting revised and lightened Japanese engine emerged in 1940 as the Ha-40.

Around this engine Kawasaki planned the Ki-60 fighter, and a lighter aircraft designated the Ki-6 Hien ('Flying Swallow').  The latter was completed in December 1941, and flew well, reaching a speed of 368 mph.  During the first half of 1942  the prototype was extensively tested, performing very well against a captured P-40E Warhawk and a German Messerschmidt Bf-109E sent to Japan by submarine.


The submarine also brought 800 Mauser MG151 cannon, which were fitted to the early Ki-61s despite the unreliable supply of electrically-fired ammunition for this weapon.


The Gifu plant delivered 2,654 (or, according to one source, 2,750) of the Ki-61-1 and -1a versions - the latter being redesigned for easier servicing and increased manouevrability.  They went into action around New Guinea in April 1943 and were given the reporting-name 'Tony' by the Allies. They were the only Japanese fighters with a liquid-cooled engine.


In 1944 the Ki-61-II was being built, but was only trickling off the production lines, and was suffering from the unreliability of its engine. Moreover the engine was not being produced in sufficient numbers.  The initial version of the -II had a larger wing and a new canopy, but it was soon replaced by the -IIa with the older and proven wing.  Only 374 of all variants of the -II were built.

In early 1945 one of 275 engineless airframes was fitted with the Ha-112 radial engine.  Although a sudden lash-up conversion this produced a staggeringly fine fighter, by far the best ever produced in Japan.  This aircraft, designated the Ki-100, was put into production with desperate haste.  One of the first Ki-100 units destroyed 14 F6F Hellcats over Okinawa in their first major encounter - without loss to themselves.  The easily-flown and serviced Ki-100 fought supremely well against Allied fighters and B-29 bombers to the very end of hostilities in the Pacific.


Kawasaki Kokuki Kogyo

Single-seat fighter

Span: 39' 5" (12 metres)Length: (Ki-61-1) 29' 4" (8.94 metres) (Ki-61-II) 30' 1" (9.16 metres)

(K-61-I) One 1,175 hp Kawasaki Ha-40 inverted-vee 12- cylinder ( liquid-cooled)
(Ki-61-II)  One 1,450 hp Kawasaki Ha-140 inverted-vee 12-cylinder (liquid-cooled)

(Ki-61-Ia) 2 x 20mm MG151/20 in wings,  2 x  12.7 mm mchine guns above engines
(Ki-61-Id)  As with K-61-Ia but with 30mm cannon in wings
(Ki-61-II) Four x 20 mm Ho-5 cannon in wings

Maximum speed (Ki-61-I) 348 mph (560 km/hour) (Ki-61-II) 379 mph (610 km/hour)
Initial climb (All Ki-61 versions) 2,200 feet (675 metres) per minute
Service ceiling (Ki-61-I) 32,800 feet (10,000 metres) (Ki-61-II) 36,100 feet (11,000 metres)

First flight (Ki-60) March 1941  (Ki-61) December 1941  (Ki-61-II) August 1943
Service delivery (Ki-61-I) August 1941

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 The main source for the this page was Bill Gunston's  "Combat Aircraft of World War II" (Salamander, London 1978).  The illustration of the Ki-61 is reproduced with thanks from the same source. +++ Last but not least, we are gratefull for the work and great support of Joe Baugher sourceing Japanese Aircraft of the Pacific War, Rene J. Francillon, Naval Institute Press, 1979, Famous Fighters of the Second World War, William Green, Doubleday, 1967, Aircraft in Profile: The Kawasaki Ki-61 Hien, Rene J. Francillon, 1966 and War Planes of the Second World War, Fighters, Volume 3, William Green, Doubleday, 1964 +++

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The Kasasaki Ki-61 Hien was unique among Japanese fighter aircraft of the Pacific War - it had a liquid-cooled engine, a long tapered nose, and high aspect-ratio wings. It had a very European look to it - in fact, when it first appeared in combat it was initially assumed to be a license-built version of either the Messerschmitt Bf 109 or perhaps some unspecified Italian aircraft. In fact, its suspected Italian ancestry may have played a role in the choosing of its Allied code name - TONY.

Most Japanese fighter aircraft had been powered by air-cooled radial engines. However, the German Daimler-Benz DB 601A liquid-cooled, inverted-vee engine (which powered the Bf 109E) had attracted considerable interest in Japan, and a license had been acquired in April 1940 by the Kawasaki Kokuki Kogyo K.K. (Kawasaki Aircraft Engineering Co Ltd) to build the German engine in Japan under the designation Ha-40. A Japanese technical team brought back a set of blueprints of the DB 601A and a few examples to serve as production patterns. The first prototype Ha-40 engine was ready in July of 1941, and the first examples began to roll off Kawasaki's Akashi engine production line in the fall of 1941.


While negotiating with Daimler Benz in Germany, Kawasaki attempted to interest the Japanese Army in various fighter aircraft powered by this engine. The Japanese Army had of course been following the combat reports from Europe with great interest, particularly the successes of fighter planes powered by liquid-cooled engines (e. g. Bf 109E, Spitfire, Hurricane). In February of 1940, the Koku Hombu instructed the airframe division of the Kawasaki Kokuki Kogyu K. K. located at Kamamingahara near Nagoya to produce two separate designs based on the DB-601A/Ha-40 engine --- the Ki-60 heavy interceptor and the Ki-61 light, all-purpose fighter.


Initial priority was given to the Ki-60 heavy interceptor. Contrary to previous Japanese philosophy, speed, rate of climb, and offensive punch were to be stressed at the expense of range and maneuverability. The Ki-60 was designed by Takeo Doi and Shin Owada and was a clean, low-winged fighter powered by a 1100 hp Daimler-Benz DB 601A liquid-cooled 12-cylinder inverted-V engine that had been purchased directly from Germany. Armament consisted of 2 fuselage-mounted 12.7-mm machine guns and two wing-mounted 20-mm Mauser MG 151 cannon imported from Germany. The first Ki-60 prototype flew in March of 1941. However, test pilots were generally displeased with its performance --- they found the aircraft to have poor maneuverability, an excessively-high wing loading, a high landing speed, and a top speed of only 342 mph (373 mph was promised). In order to correct some of these deficiencies, the second prototype was provided with a wing of increased area and was fitted with a revised cowling having better streamlining. Maximum speed was boosted to 348 mph and maneuverability was improved somewhat. The third prototype was refined still further, and the Mauser cannon were replaced by a pair of 12.7-mm machine guns in an attempt to save some weight. However, even with these changes, the maximum speed was still only a rather disappointing 354 mph, and the Ki-60 project was shelved in favor of Kawasaki's other project, the lighter and faster Ki-61.


The Ki-61 was a lighter, all-purpose adaptation of the Ki-60. It was also designed by Takeo Doi and Shin Owada and was fitted with a high aspect-ratio, large area wing which was designed to provide good maneuverability and long endurance. It was two feet longer than the Ki-60, and the wings were five feet greater in span. The engine was also the Kawasaki Ha-40, the license-built version of the DB-601A. Armament consisted of two 12.7 mm machine guns in the fuselage and either a pair of 7.7 mm or 12.7 mm machine guns were fitted to the wings. A large coolant radiator was mounted on the fuselage belly at the position of the wing trailing edge.


Flight tests of the Ki-61 prototype began in December of 1941. Flight tests met the most sanguine hopes of the designers --- a maximum speed of 367 mph at 19,685 feet was reached. The wing loading was high in comparison with other Japanese fighters, but the diving speed was good and the armor protection, self-sealing tanks, and heavy armament were all commented upon favorably. During competitive tests against an imported Bf 109E and a captured Curtiss P-40E, the Ki-61 was judged to have the best overall performance.


In late 1942, the design was accepted for production under the designation Army Type 3 Fighter Model 1. It was assigned the popular name Hien (Swallow). The thirteenth Ki-61 was the first machine which was built with production tooling and was completed in August of 1942. It differed from the prototypes in deleting a small window on each side of the fuselage ahead of the windshield.


There were two initial production variants, which differed from each other in the armament fitted: the Ki-61-Ia (Model 1A) armed with two fuselage- mounted 12.7-mm machine guns and two wing-mounted 7.7-mm machine guns and the Ki- 61-Ib (Model 1B) in which the wing guns were replaced by 12.7-mm units. The powerplant was the 1100 hp Kawasaki Ha-40 twelve- cylinder liquid cooled inverted-vee engine.


Initial deliveries were made in February 1943 to the 23rd Dokuritsu Dai Shijugo Chutai at Ota, which acted as a conversion and training unit. The Hien initially entered combat in April 1943 when the 68th and 78th Sentais were transferred to the New Guinea theatre of operation. The aircraft subsequently appeared in every theatre in which the Japanese Army was involved. The Ki-61 immediately proved itself to be better suited for combat against its heavier-armed Allied opponents than was the Ki-43 Hayabusa. Although it was not as maneuverable as the earlier Ki-43, the Ki-61 had heavier armament, good armor protection for the pilot, and self-sealing fuel tanks. The Hien could be pushed over into a 45 degree dive very rapidly, and its diving performance was far superior to that of any other Japanese fighter. Its high diving speed worked to advantage against Allied fighters which relied on hit and run attacks from higher altitudes. In defensive operations, the Hien was especially difficult to counter, since the aircraft seldom offered a good target. When engaged in combat at a disadvantage, it could often escape by going into a half-roll followed by a dive, or else it would turn in and under the opposing plane, often getting in a deflection shot. The Hien completely outclassed the Curtiss P-40 in most combat encounters, unless the Allied fighter was being flown by the most experienced of pilots. The Hien was well-liked by its pilots and respected and feared by its opponents. However, the Ha-40 engine proved to be a maintenance headache, especially in the prevailing hot and damp weather of the New Guinea theatre. Main-bearing failures and oil-system faults were the primary problems. In addition, the power ratings of individual Ha-40 engines would vary greatly from one example to another, owing to poor quality control during manufacture.


Combat experience showed that the Hien was still somewhat underarmed, especially when it was going up against well-protected Allied bombers. Pending the availability of indigenous cannon, plans were made to replace the wing-mounted machine guns of the Ki-61-Ia and Ib aircraft with Mauser MG 151 20 mm cannon imported from Germany. Since space in the wing was limited, the cannon had to be mounted on their sides, with a small underwing fairing covering the breech. Since the recoil forces from the cannon were larger than those from the machine guns, some local wing strengthening was required. However, as the war began to turn against Japan, the numbers of these German-supplied cannon became limited, and only 388 Ki-61-Ia and -1b Hiens actually received these guns.

One Ki-61 was modified to test a surface evaporation cooling system proposed for the Ki-64 experimental high-speed fighter. This had its large ventral radiator replaced by a smaller retractable unit located further forward. This unit was meant only for use on the ground, with inflight cooling being provided by steam evaporation through wing condensers.


Operations from New Guinea, New Ireland, and New Britain had shown that the Hien was difficult to maintain in the field. In an attempt to improve the maintainability of the basic design, the Ki-61-I-KAIc version was introduced onto the production line. In order to simplify maintenance in the field, the fuselage was slightly longer and was provided with a detachable rear section. The wings were strengthened, which allowed an increase in the diving speed. Provisions were made for the mounting of stores pylons underneath the wings outboard of the wheel wells. The retractable tailwheel was replaced by a fixed unit. Aware that the supply of German MG 151 cannon could be curtailed at any time, the Japanese had begun developing a comparable weapon of indigenous design, the Ho-5. The Ki-61-I-KAIc (Model Ic) used a pair of domestically-produced Type Ho-5 20 mm cannon mounted in the fuselage and a pair of 12.7-mm machine guns mounted in the wings. The first Ki-61-I-KAIc was manufactured in January 1944. Since the Ho-5 cannon were not immediately available in adequate quantity, the Ki-61-I-KAIc version was manufactured in parallel with the earlier Ki-61-Ib. The Ki-61-I-KAIc finally supplanted the earlier model on the production line in August of that year. A total of 1274 Model Ics were built, which accounted for over half the Hiens built.

The Ki-61-I-KAId was a specialized bomber interceptor version armed with a pair of 30-mm cannon in the wings and two 12.7-mm machine guns in the fuselage. Only a few of these variants were built.


The Hien appeared in the Philippines late in 1944, serving with the 17th, 18th, and 19th Sentais. It appeared over Formosa and Okinawa with the 19th, 37th 59th, and 105th Sentais, and the 23rd Doikuritsu Dai Shijugo Chutai. It also served with the 18th, 23rd, 28th, 55th, 56th, 59th, and 244th Sentais in the final defense of the Japanese home islands. Over Japan, it fought against B-29s and against US Navy carrier-based aircraft. Against the high-flying B-29s, the Hien lacked the necessary high-altitude performance. In attacks on B-29 bombers, the Hien would often be used in ramming attacks, the pilot jumping clear immediately before impact. When the Iwo Jima-based P-51 Mustang finally started to appear over Japan, the Hien was definitely outclassed.

A total of 2654 production Ki-61-I Hiens were built (1380 Ia and Ib, 1274 KAIc and KAId). By the spring of 1944, production of the Hien had fallen to a low level because of shortages of Ha-40 engines, with no solution having been found for the bearing failure problems. Production was finally terminated in January of 1945.


Specification of Kawasaki Ki-61-1b Army Type 3 Fighter Model 1b:


One Army Type 2 twelve-cylinder liquid cooled engine (Kawasaki Ha-40) rated at 1175 hp for takeoff and 1080 hp at 11,480 feet. Performance: Maximum speed 368 mph at 15,945 feet. Cruising speed 249 mph at 13,125 feet. An altitude of 16,400 feet could be reached in 5 minutes 31 seconds. Service ceiling 37,730 feet. Normal range 373 miles, maximum range 684 miles.

Dimensions: Wingspan 39 feet 4 7/16 inches, length 28 feet 8 1/2 inches, height 12 feet 1 11/16 inches, wing area 215.3 square feet.

Weights: 4872 pounds empty, 6504 pounds loaded, 7165 pounds maximum. Armament: Two fuselage-mounted 12.7 mm Type 1 (Ho-103) machine guns and two wing-mounted 7.7 mm Type 89 machine guns (Ki-61-Ia). Two fuselage-mounted 12.7 mm Type 1 (Ho-103) machine guns and two wing-mounted 12.7 mm Type 1 (Ho-103) machine guns (Ki-61-Ib). Some Ki-61-Ia and -Ib aircraft had the wing guns replaced by 20-mm Mauser MG-151/20 cannon.


Specification of Kawasaki Ki-61-I-KAIc Army Type 3 Fighter Model 1c:


One Army Type 2 twelve-cylinder liquid cooled engine (Kawasaki Ha-40) rated at 1180 hp for takeoff and 1100 hp at 11,480 feet. Performance: Maximum speed 366 mph at 13,980 feet. An altitude of 16,400 feet could be reached in 7 minutes. Service ceiling 32,810 feet. Maximum range 1120 miles.

Dimensions: Wingspan 39 feet 4 7/16 inches, length 29 feet 4 inches, height 12 feet 1 11/16 inches, wing area 215.3 square feet. Weights: 5798 pounds empty, 7650 pounds loaded.

Armament: Two fuselage-mounted 20 mm Ho-5 cannon and two wing-mounted 12.7 mm Type 1 (Ho-103) machine guns and two wing-mounted 12.7 mm Type 1 (Ho-103) machine guns.




Shortly after beginning production of the Ha-40 engine, the Kawasaki corporation began work on a more powerful version of this engine, designated Ha-140. This engine was to emphasize high-altitude performance, and work began on a Hien derivative to accommodate this new engine. This derivative was given the temporary designation Ki-61-II-KAI. It retained the original wing of the Hien, married to a revised fuselage with a longer nose and a strengthened airframe. The cockpit canopy was revised for improved vision. A redesigned vertical fin with a greater area was fitted.

Even though the Ha-140 engine still had a lot of mechanical problems (crankshaft failures being quite common), the design was accepted for production as the Ki-61-II Army Type 3 Fighter Model 2.

Two versions of the Model 2 were built--the Ki-61-IIa Model 2A with two 12.7 mm machine guns in the wings and two 20-mm Ho-5 cannon in the fuselage, and the Ki-61-IIb Model 2B with four 20 mm Ho-5 cannon.

The Model 2 Hien never entirely supplanted the earlier Model 1 in operational units, since its Ha-140 engine continued to suffer from lots of problems even after full production had begun. This engine was subject to frequent failures in its main bearings, in its superchargers, and in its oil and coolant systems. In addition, the lack of skilled workers in the engine manufacturing plant resulted in rather poor quality control, and only rarely did the Ha-140 engine give its full rated power. However, when the Ha-140 engine was working well, it could deliver 1500 hp for takeoff and 1250 hp at 18,700 feet, and the Model 2 Hien proved to be an effective interceptor and was the only Army fighter capable of maintaining combat formation at the operating altitude of the B-29. Of the Ki-61-IIa and IIb fighters built, about one-third were destroyed in air raids, and the remainder were assigned to duty as interceptors.

Chronic engine problems and shortages resulted in lots of Model 2 airframes sitting around in factory yards waiting for powerplants. This problem was exacerbated even further on January 19, 1945 when a B-29 raid destroyed Kawasaki's Akashi engine plant. The chronic shortage of engines caused production of the Model 2 Hien to be suspended. By the time that production was suspended, 374 Model 2s had been built, but 30 of these were destroyed on the ground prior to delivery and 275 were built without engines.

What to do with these airframes sitting around waiting for engines? That is another story, which will be considered in the Ki-100 installment of this series.


Specification of the Kawasaki Ki-61-IIa Army Type 3 Fighter Model 2A:


One Kawasaki Ha-140 twelve-cylinder liquid-cooled engine rated at 1500 hp for takeoff and 1250 hp at 18,700 feet.

Performance: Maximum speed 379 mph at 19,685 feet, an altitude of 16,400 feet could be attained in 6 minutes. Service ceiling 36,090 feet. Normal range 684 miles, maximum range 995 miles.

Dimensions: Wingspan 38 feet 4 7/16 inches, length 30 feet 0 5/8 inches, height 12 feet 1 11/16 inches, wing area 215.3 square feet. Weights: 6261 pounds empty, 8333 pounds loaded, 8433 pounds maximum Armament: two fuselage-mounted 20-mm Ho-5 cannon and two wing-mounted 12.7 mm Type 1 (Ho-103) machine guns. Two 551 pounds could be carried on underwing hardpoints.



The Ki-61-III was to have been a modified version of the Ki-61-II with various aerodynamic refinements including the use of an all-round vision canopy. Only one aerodynamic prototype was produced, this aircraft being produced by fitting an all-round vision canopy to a stock Ki-61-II. This version was never produced, being abandoned in favor of the radial-engined version of the Hien, the Ki-100. However, the new all-round vision canopy was eventually incorporated into later production models of the Ki-100.

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