Picture - A Ki-61 -I -Otsu

Role - Fighter aircraft
Manufacturer - Kawasaki Aircraft
(Kawasaki Heavy Industries)
Designed by - Takeo Doi and Shin Owada
First flight - December 1941
Introduced - 1943
Retired - 1945
Primary users - IJA Air Force
Chinese Nationalist Air Force, Indonesian People's Security Force, People's Liberation Army Air Force
Number built - 3,159
Variants - Kawasaki Ki-100

The Kawasaki Ki-61 Hien (roughly "flying swallow") was a Japanese World War II fighter aircraft used by the Imperial Japanese Army Air Force. The Allied code name assigned by the United States War Department was "Tony". The Japanese Army designation was "Army Type 3 Fighter".[1] It was the only mass-produced Japanese fighter of the war to use a liquid-cooled inline V engine.

Picture - A factory fresh Ki-61-I-Ko being ferried to either the 68th or 78th Sentai in New Guinea; it has yet to receive the distinctive dark green "palm leaf" pattern which was usually applied by front-line units in the Southern theatre, nor does it have the usual black anti-glare panel forward of the cockpit.

Design and development

A factory fresh Ki-61-I-Ko being ferried to either the 68th or 78th Sentai in New Guinea; it has yet to receive the distinctive dark green "palm leaf" pattern which was usually applied by front-line units in the Southern theatre, nor does it have the usual black anti-glare panel forward of the cockpit.

The Ki-61 was designed by Takeo Doi and his deputy Shin Owada. It was designed in response to a tender by the Technical Branch of the Imperial Army Air Headquarters - the Koku Hombu - late in 1939, for two fighters. Each was to be built around the Daimler-Benz DB 601Aa, a derivative of which was to be manufactured as the Ha-40 by Kawasaki at its Akashi plant. The first design, known as the Kawasaki Ki-60, was for a heavily-armed specialised interceptor, which would have a high wing loading [2]; the second, the Ki-61 was a more lightly-loaded and armed general-purpose fighter to be used mainly in an offensive, air superiority role at low to medium altitudes[3]. Both single-seat, single-engine fighters used the same basic construction, being of all-metal alloys with semi-monocoque fuselages and three-spar wings, with alloy-framed, fabric-covered ailerons, elevators and rudders. Priority was given to the Ki-60, which first flew in April 1941. Design of the Ki-61 did not begin until December 1940. Although the Ki-61 was broadly similar to the Ki-60, it featured several refinements using lessons learned from the disappointing flight characteristics of the earlier design. [4]

Picture - Unusual wartime photo of a captured Ki-61 being tested by the USAAF

The all-metal, semi-monocoque fuselage was basically oval in cross-section, changing to a tapered, semi-triangular oval behind the cockpit canopy, with a maximum depth of 1.35 m (4 ft 5 in). An unusual feature of the Ki-61 was that the engine bearers were constructed as an integral part of the forward fuselage, with the cowling side panels being fixed. For servicing or replacement, only the top and bottom cowling panels could be removed. A tapered, rectangular supercharger air intake was located on the port-side cowling. Behind the engine bulkhead were the ammunition boxes feeding a pair of 12.7 mm (.50 in) Ho-103 machine guns which were set in a "staggered" configuration (the port weapon slightly further forward than that to starboard) in a bay just above and behind the engine. The breeches partly projected into the cockpit, above the instrument panel. The Ho-103 was a light weapon for its caliber (around 23 kg/51 lb) and fired a light shell, but this was compensated for by its rapid rate of fire. The ammunition capacity was limited, having only around 250 rounds for each weapon. A self-sealing fuel tank with a capacity of 165 L (44 US gal) was located behind the pilot's seat. The windshield was armoured and there was a 13 mm (.51 in) armour plate behind the pilot. The radiator and oil cooler for the liquid-cooled engine were in a ventral location below the fuselage and wing trailing edge, covered by a rectangular section fairing with a large, adjustable exit flap.[4].

Picture - An ex-23rd Sentai, 2nd Chutai Ki-61 found and photographed at Inba airbase by USAAF personnel in 1946.

The evenly-tapered wings had an aspect ratio of 7.2 with a gross area of 20 m² (215.28 ft²) and featured three spars; a Warren truss main spar and two auxiliary spars. The rear spar carried the split flaps and long, narrow-chord ailerons, while the front spar incorporated the undercarriage pivot points. The undercarriage track was relatively wide at 4 m (13 ft 1.5 in). Each wing had a partially self-sealing 190 L (50 US gal) fuel tank behind the main spar, just outboard of the fuselage. A single weapon (initially a 7.7 mm/0.303 in Type 89 machine gun) was able to be carried in a weapons bay located behind the main spar. [4]

The first prototype of the San-shiki-Sentohki ichi gata (Type 3 Fighter, Model 1, the official IJAAF designation) first flew in December 1941. Although test pilots were enthusiastic about its self-sealing fuel tanks, upgraded armament, and good dive performance, the wing loading of 146.3 kg/m² (30 lb/ft²) at an all-up weight of 2,950 kg (6,500 lb) was viewed with scepticism by many of the senior officers of the Koku Hombu, who still believed in the light, highly manoeuvrable, lightly armed fighter epitomised by the then new Ki-43-I-Hei which had a wing loading of 92.6 kg/m² (19 lb/ft²) (even that was considered borderline).[5]

To address these concerns, Kawasaki staged a fly-off between two Ki-61 prototypes and the Ki-43-I, a pre-production Ki-44-I, a LaGG-3 (flown to Manchuria by a defector), a Bf 109E-3, and a captured P-40E Warhawk. The Ki-61 proved the fastest of all the aircraft and was inferior only to the Ki-43 in manoeuvrability.[6][7][8][5]

The Ki-61 was the last of the DB-601-powered fighters and it was soon overshadowed by fighters with more powerful engines. By the time it first flew in December 1941 – only one year after the Macchi's first flight and three years after the Bf 109E – the DB-601 was already underpowered compared to the new 1,120 kW (1,500 hp) inline or 1,491 kW (2,000 hp) radial engines being developed (and already nearing the mass-production stage) to power the next generation of combat aircraft: the P-47, Fw 190 and Bf 109 G. Moreover, the inline Ha-40 engine proved to be an unreliable powerplant.[9] [10]

The DB-601 engine on which the Hien was based was designed with very critical tolerance limits, and in the Ha-40 Japanese technicians developed a lighter version (by roughly 30 kg/70 lb) that required even higher tolerances. Reaching these levels proved to be a "stretch" for Japan's aviation manufacturing capabilities, which was further complicated by the variable quality of the materials, fuel, and the lubricants needed to run this sensitive, high-performance engine smoothly. The Japanese equivalent of the more powerful DB-605 engine was the Ha-140, which was fitted onto the Type 3 to produce the Ki-61-II high-altitude interceptor.[9]

Compared to the Ki-61-I, the Ki-61-II had 10% greater wing area, more armor, and – with the Kawasaki Ha-140 engine – an increased power of 1,120 kW (1,500 hp). After overcoming initial fuselage and wing stability problems, the new interceptor reverted to the original wing and was put into service as the Ki-61-II-KAI. However, the Ha-140 engine had reliability problems of its own which were never fully resolved, and around half of the first batch of engines delivered were returned to the factory to be re-built. Shortly after, a US bombing raid on 19 January 1945 destroyed the engine factory in Akashi, Hy?go, and 275 Ki-61-II-KAI airframes without engines were converted to use the Mitsubishi Ha-112-II radial engine, resulting in the Ki-100. While the Ha-112 solved the problems encountered with the Ha-140, the new engine still had a weakness: the lack of power at altitude, which diminished its ability to intercept high-flying B-29s relative to the Ki-61-II.[9]

During testing, The Hien proved capable [11] but several shortcoming were subsequently revealed in operational service, namely lack of armor protection, and a sub-standard engine that eventually led to a new engine being considered.[12]

Operational history

The new Ki-61 Hien fighters entered service with a special training unit, the 23rd Chutai, and entered combat for first time in spring 1943 during the New Guinea campaign. Initially, due to its unusual appearance for a Japanese fighter, the Allies believed it to be of German or Italian origin, possibly a license-built Bf 109; the Italian-like appearance led to its code name of "Tony".[13][14]

The first Sentai (wing) fully equipped with the Hien was the 68th in Wewak, New Guinea, followed by the 78th Sentai stationed at Rabaul. Both units were sent into a difficult theatre where jungles and adverse weather conditions, coupled with a lack of spares, quickly undermined the efficiency of both men and machines; this was especially the case for new-design aircraft, which are particularly prone to teething problems, as the Ki-61s were. Initially, this campaign went successfully for the Japanese Army Air Force (JAAF), but when the Allies re-organized and enhanced the combat capabilities of their air forces, they gained the upper hand against the JAAF.[10].

High aircraft losses were experienced in some incidents during this campaign. For example, while in transit between Truk and Rabaul, the 78th lost 18 of its 30 Ki-61s. Other units were involved and sometimes, even more unfortunate: only two of (possibly) 24 Nakajima Ki-49s reached Rabaul in June 1943. Almost all of the modern Japanese aircraft engines, especially the Ki-61's liquid-cooled engines, suffered a disastrous series of failures and ongoing problems,[10] which resulted in the obsolescent Ki-43 forming the bulk of the JAAF's fighter capability. At the end of the campaign, nearly 2,000 Japanese aircraft had been lost in continuous air attacks from up to 200 Allied aircraft at one time (among them, around half were B-24s and B-25s armed with fragmentation bombs[10] After the Japanese retreat, over 340 aircraft wrecks were later found at Hollandia.[10]

Even with these problems, there was a general Allied concern regarding this new fighter:

The Hien entered combat in the spring of 1943 in the New Guinea war zone, covering [mainland] New Guinea, the Admiralty Islands, New Britain and New Ireland. The new Japanese fighter caused some pain and consternation among Allied pilots, particularly when they found out the hard way that they could no longer go into a dive and escape as they had from lighter Japanese fighters. ... General George Kenney [Allied air forces commander in the Southwest Pacific] found his P-40 Warhawks completely outclassed, and begged for more P-38 Lightnings to counter the threat of the new enemy fighter.[15]

The Ki-61 was also utilised in Southeast Asia, Okinawa, China and as an interceptor during US bombing raids over Japanese home islands, including against B-29 Superfortresses. The Ki-61 was notable for many reasons: initially identified as of either German or Italian origin, these aircraft were capable of matching Allied aircraft such as the P-40 in speed, and as evaluation had already showed, were superior in almost every respect. However, the armament of the early Hien was lighter, but still sufficient for most purposes. Some authors claim that the P-38 was measurably superior.[16] The Ki-61 carried a great deal of fuel, but due to having self-sealing fuel tanks, it did not have the reputation for being "easily flammable" as were many other Japanese aircraft.[9]

Due to the additional weight, the Ki-61's performance and agility suffered when its armament was increased, but it still remained capable with a 580 km/h (313 kn) maximum speed. The cannon armament was essentially needed to counter the Allied bombers, which proved to be difficult to shoot down with only 12.7 mm (.50 in) machine guns. The empty and maximum weights for the Ki-61 prototype (2 × 12.7 mm/50 in + 2 × 7.7 mm/.303 in) were 2,238 kg (4,934 lb) and 2,950 kg (6,504 lb), respectively; for the Ki-61-I basic (4 × 12.7 mm/.50 in) 3,130 kg (6,900 lb); and for the Ki-61-KAI (2 × 12.7 mm/.50 in + 2 × 20 mm), 2,630 kg (5,798 lb) and 3,470 kg (6,750 lb).[9]

A number of Ki-61s were also used in Tokkotai (kamikaze) missions launched toward the end of the war. The Ki-61 was delivered to 15th Sentai (groups/wings), as well as some individual Chutaicho (junior operational commanders) in other Sentai, and even to operational training units in the JAAF. The aircraft was largely trouble-free in service except for the liquid-cooled engine which tended to overheat when idling on the ground and suffered from oil circulation and bearing problems.[17]

Ki-61 Special Attack Unit

The tactic of using aircraft to ram American B-29s was first recorded in late August 1944, during a raid when B-29s from Chinese airfields were sent to bomb the steel factories at Yawata. Sergeant Shigeo Nobe of the 4th Sentai intentionally sliced his Kawasaki Ki-45 into a B-29; debris from the explosion following this attack severely damaged another B-29, which was also went down.[18][19] Other attacks of this nature followed, as a result of which individual pilots determined it was a quite practical way to destroy B-29s.[20]

On 7 November 1944, the officer commanding the 10th Hiko Shidan made ramming a matter of policy by forming ramming attack flights specifically to oppose the B-29s at high altitude. The aircraft were stripped of their fuselage armament and protective systems in order to attain the required altitudes. Although the term "kamikaze" is often used to refer to the pilots undertaking these attacks, the word was not used by the Japanese military.[21]

The units assigned to the 10th included the 244th Hiko Sentai, then commanded by Captain Takashi Fujita who organised a ramming flight named "Hagakure-Tai" ("Special Attack Unit"), which was composed of three sections: the 1st Chutai "Soyokaze", 2nd Chutai "Toppu", and the 3rd Chutai known as "Mikazuki".

First Lieutenant Toru Shinomiya was selected to lead the attack unit, he would became famous by ramming an American B-29 and living to tell the tale. Shinomiya attacked the B-29 on 3 December 1944, and brought himself and his damaged aircraft home; Shinomaya's Ki-61, which had lost most of the port outer wing, was subsequently put on display in a major department store in Tokyo. He would eventually lose his life as a Tokkotai pilot in the battle for Okinawa. Another 244th pilot, Corporal Masao Itagaki, performed a similar feat on the same occasion, but had to parachute from his damaged fighter. A third pilot, Sergeant Nakano, of the Hagakure-Tai of the 244th rammed another B-29 and crash-landed his stripped-down Ki-61 in a field. These three pilots were the first recipients of the Bukosho, Japan's equivalent to the Victoria Cross or Medal of Honor, which had been inaugurated on 7 December 1944 as an Imperial Edict by Emperor Hirohito (there are 89 known recipients, most of whom fought and scored against B-29s.)[22][23] Sergeant Shigeru Kuroishikawa was another distinguished member in the unit.

The existence of the ramming unit had been kept confidential until then, but it was officially disclosed in the combat results announcement and officially named "Shinten Seiku Tai" ("Heart of Heaven Intercept Unit") by the Defense GHQ.

But these pilots gained no reprieve and despite their successes they were obligated to continue these deadly and dangerous ramming tactics until they were killed or else wounded so badly that they could no longer fly. They were regarded as doomed men and were celebrated among the ranks of those who were going to certain death as Tokkotai (kamikaze) pilots.[24]

Some other Ki-61 pilots also became well-renowned, among whom was Major Teruhiko Kobayshi who was credited by some with a dozen victories mostly due to conventional attacks against B-29s.[25]

Ki-61 units

The Hikosentai, usually referred to as Sentai, was the basic operational unit of the IJAAF, composed of three or more Chutai (companies or squadrons). A Sentai had 27 to 49 aircraft, with each Chutai having 16 aircraft and pilots plus a maintenance and repair unit. Several sentai had other units under their operational control, most notably the Hagakure-Tai ("Special Attack Units") of 244 Sentai. By 1944, with the depredations of Allied attacks on supply lines and airfields, as well as the loss of pilots and aircraft through combat attrition and accidents, few sentai were able to operate at full strength.

Variants

Note: Ko, Otsu, Hei and Tei are the Japanese equivalents to a, b, c, d. Kai (modified) was also used for some models of the Ki-61.

Ki-61
12 original prototypes.
Ki-61-I-Ko
The first production version. This version had a fully-retractable tailwheel and two 7.7 mm (0.303 in) Type 89 machine guns in the wings and two synchronized 12.7 mm (0.50 in) Ho-103 machine guns in the fuselage forward decking. The wings had racks outboard of the wheelwells, which were capable of carrying one 151 L (40 gal) drop tank or a light bomb. Weights: 2,238-2,950 kg (wing loading 147 kg/m2)[9].
Ki-61-I-Otsu
The second production fighter variant. As it was found the armament was too light against allied aircraft and the tailwheel retraction mechanism was unreliable, the plane was modified accordingly. Two 12.7 mm (.50 in) Ho-103 machine guns replaced the wing 7.7 mm (.303 in) machine guns, with modifications to the upper-wing bulges, and the tailwheel doors were removed and the tailwheel locked in the "down" position (although the mechanism was still intact). Max takeoff weight 3,130 kg[9].
Ki-61-I-Hei
800 German-made 20 mm Mauser MG 151/20 cannons and ammunition supplies were imported to Japan by submarine. The Hei was built in conjunction with the Otsu variant on the Kawasaki production lines but some "conversion kits" were directly sent to New Guinea. In this variant, the wing machine guns were replaced by Mauser cannons. The fuselage was longer (engine bulkhead forwarded of 19 cm, added a small fuel tank). Trial fittings found that these could be placed into the existing wing if the gun was laid on its side and a fairing was provided on the underside of the wing for clearance of the breech mechanism. 388 Ki-61s were so modified; there is now some doubt as to whether the Hei ("d") designation was used.[31] . Max takeoff weight 3,470 kg, max speed 580 kmh at 5,000 m, time to that height was 7 minutes. The firs one was completed in january 1944[9].
Ki-61-I-Tei
This machine featured two 12.7 mm (.50 in) Ho-103s in the modified (stronger) wings, provisions of external storage using fixed underwing pylons, and a non-retractable tail wheel. The forward fuselage was elongated by 190 mm (7.5 in) just after the exhaust line and forward of the windscreen to make room for the installation of Japanese 20 mm Ho-5 cannon in the fuselage decking (the same as with Hei version). The continued supply of MG 151's via submarine was not able to be guaranteed and the Ho-5 was ready. Several internal changes were also made. These included the simplification of several systems for increased dependability and ease of maintenance. The rear section of the fuselage was also made to be easily removable to further facilitate the ease of repair work. [32]
Ki-61-I-KAId
Interceptor variant with 2 × 12.7 mm (.50 in) fuselage machine guns and 2 × 30 mm (1.18 in) wing cannon.
Ki-61-I- w.c.e.s.
An experimental aircraft with a wing cooling evaporation system, modelled on that used by the Heinkel He 100. It was the fastest Ki-61 built, achieving 630 km/h (395 mph), and the last with a retractable tail wheel.
Ki-61-II
Prototype with 10% greater wing area and a slightly different airfoil. An Ha-140 engine with 1,120 kW (1,500 hp) for takeoff was fitted; the cowling panels were redesigned and the supercharger air intake was longer. A redesigned windscreen incorporating an extra panel was mounted further forward. The transparency to the rear of the sliding canopy was redesigned to increase rearward visibility. The prototype was first flown in December 1943; flight trials showed that the new wing was unsatisfactory and only eight Ki-61-IIs were built.
Note
Because of the unreliability of the Ha-140 and the destruction of the Akashi plant by a B-29 bombing attack the bulk of the Ki-61-II-KAIs built were airframes only, which were later converted to Ki-100-Is.
Ki-61-II-KAI
Pre-production version which reverted back to the Ki-61-I-Tei wing, a 220 mm (8.7 in) fuselage stretch, enlarged rudder, and Ha-140 engine; 30 built.
Ki-61-II-KAIa
Armed with 2 x 12.7 mm (.50 in) machine guns in the wings and 2 x 20 mm cannon in the fuselage.
Ki-61-II-KAIb
Armed with 4 x 20 mm cannon.
Ki-61-III
One prototype only. This version had a cut-down rear fuselage and a canopy design which was later used by the Ki-100-II.

A total of 3,159 Ki-61 were built.[33]

Specifications (Ki-61-I-KAIc)

Data from The Great Book of Fighters[35]

General characteristics

- Crew: One
- Length: 8.94 m (29 ft 4 in)
- Wingspan: 12.00 m (39 ft 4 in)
- Height: 3.70 m (12 ft 2 in)
- Wing area: 20.00 m² (215.28 ft²)
- Airfoil: NACA 2R 16 wing root, NACA 24009 tip

- Internal fuel capacity: 550 l (121 Imp gal)
- External fuel capacity: 2 x 200 l (44 Imp gal) drop tanks

- Empty weight: 2,630 kg (5,800 lb)
- Loaded weight: 3,470 kg (7,650 lb)
- Powerplant: 1× Kawasaki Ha-40 liquid-cooled inverted V-12, 875 kW (1,175 hp)

Performance

- Maximum speed: 580 km/h (360 mph) at 5,000 m (16,405 ft)
- Range: 580 km (360 mi)
- Service ceiling: 11,600 m (38,100 ft)
- Rate of climb: 15.2 m/s (2,983 ft/min)
- Wing loading: 173.5 kg/m² (35.5 lb/ft²)
- Power/mass: 0.25 kW/kg (0.15 hp/lb)
- Time to altitude: 7.0 min to 5,000 m (16,405 ft)

Armament

- 2 x 20 mm Ho-5 cannon, 120 rpg each
- 2 x 12.7 mm (0.50 in) Ho-103 machine guns, 250 rpg each
- 2 x 250 kg (551 lb) bombs

Related development

- Kawasaki Ki-60
- Kawasaki Ki-100

Comparable aircraft

- Heinkel He 100
- Macchi C.202
- Messerschmitt Bf 109
- LaGG-3

References
Notes

1. Mondey 2006, p. 144.
2. Note: The Nakajima Ki-44 was selected as the standard IJAAF interceptor fighter and followed broadly similar specifications to the Ki-60.
3. Note: Nakajima designed a similar fighter, the Ki-62, also powered by an Ha-40. This design later became the basis for the Ki-84.
4. a b c Green and Swanborough, 1976, pp. 18-23
5. a b Green and Swanborough 1976, p. 23.
6. Francillon 1966, p. 319.
7. Green 1975, p. 78.
8. Francillon, 1979, p. 114.
9. a b c d e f g h Gibertini 1998, pp. 6-13.
10. a b c d e Vaccari 2000, pp. 82–90.
11. USN report on captured Ki-61 (pdf file)
12. [1]
13. Francillon 1966, p. 316.
14. Crosby 2002, p. 94.
15. Francillon, Dr. Réne J. Japanese Aircraft of The Pacific War (2nd ed.), Naval Institute Press 1979.
16. Green and Swanborough 1976, p. 29.
17. Green and Swanborough 1976, pp. 27-28.
18. Note: The B-29s were Colonel Robert Clinksale's B-29-BW 42-6334 Gertrude C and Captain Ornell Stauffer's B-29-BW 42-6368 Calamity Sue, both from the 486th BG.
19. Pacific War Chronology; August 1944 Retrieved: 12 June 2008
20. Takaki 2001.
21. Webpage on Kamikaze from Japanese and American perspectives Retrieved: 12 April 2008.
22. Sakaida 1997, pp. 67-70.
23. Bukosho described Retrieved: 3 June 2008.
24. Japanese website dedicated to the Tokkotai JAAF and JNAF Retrieved: 7 June 2008
25. Sakaida 1997, pp. 74-75.
26. Note: There is an inconsistency in the locations given; Kagamigahara is listed by Sakaida as being in the Saitama Prefecture
27. Ki-61 No. 640 Retrieved: 8 June 2008
28. Pacific Aircraft Wrecks, list of airfields on Formosa Retrieved: 7 June 2008
29. Sakaida 1997, pp. 82-87.
30. Bueschel 1971, pp. 47-49.
31. Ki-61 survey Retrieved: 11 June 2008
32. Mondey 2006, p. 146.
33. The Kawasaki Ki-61 Hien ("Tony") & Ki-100. Retrieved: 20 February 2007.
34. Indonesian aviation 1945 -1950
35. Green, William and Swanborough, Gordon. The Great Book of Fighters. St. Paul, Minnesota: MBI Publishing, 2001. ISBN 0-7603-1194-3.

Bibliography

- Bílý, Miroslav . Kawasaki Ki-61 a Ki.100 (Profily letadel II. Svetové války no.4) (in Czech with English and German captions). Praha, Czech Republic: Modelpres, 1992. ISBN 80-901328-0-4.
- Bueschel, Richard M. Kawasaki Ki.61/Ki.100 Hien in Japanese Army Air Force Service, Aircam Aviation Series No.21. Canterbury, Kent, UK: Osprey Publications Ltd, 1971. ISBN 0-85045-026-8.
- Crosby, Francis. Fighter Aircraft. London: Lorenz Books, 2002. ISBN 0-7548-0990-0.
- Francillon, Réne J. Japanese Aircraft of the Pacific War. London: Putnam & Company Ltd., 1970 (2nd edition 1979). ISBN 0-370-30251-6.
- Francillon, Réne J. The Kawasaki Ki-61 Hien (Aircraft in profile number 118). Leatherhead, Surrey, UK: Profile Publications, 1966. ASIN B0007KB5AW.
- Gibertini, Giorgio. "Rondini Giapponesi" (in Italian).Aerei Nella Storia N.8, August 1998. Parma, Italy: West-ward edizioni.
- Gallagher, James P. "Meatballs and Dead Birds; A Photo Gallery Of Destroyed Japanese Aircraft In World War II". Stackpole Books, 2004. ISBN 0-8117-3161-8
- Green, William. "An Oriental Swallow." Air International Vol. 9, no. 2, August 1975.
- Green, William. Warplanes of the Second World War, Volume Three: Fighters. London: Macdonald & Co. (Publishers) Ltd., 1961 (seventh impression 1973). ISBN 0-356-01447-9.
- Green, William and Swanborough, Gordon. WW2 Aircraft Fact Files: Japanese Army Fighters, Part 1. London: Macdonald and Jane's, 1976. ISBN 0-356-08224-5.
- Gunston, Bill. World Encyclopedia of Aircraft Manufacturers: From the Pioneers to the Present Day. Annapolis, Maryland: Naval Institute Press, 1993. ISBN 1-55750-939-5.
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- Janowicz, Krzysztof. 68 Sentai (in Polish). Lublin, Poland: Kagero, 2003. ISBN 83-89088-01-0.
- Januszewski, Tadeusz and Jarski, Adam. Kawasaki Ki-61 Hien, Monografie Lotnicze 5 (in Polish). Gda?sk, Poland: AJ-Press, 1992. ISSN 0867-7867.
- Mondey, David. The Hamlyn Concise Guide to Axis Aircraft of World War II. London: Bounty Books, 2006. ISBN 0-753714-60-4.
- Sakaida, Henry. Japanese Army Air Force Aces 1937-45. Botley, Oxford, UK: Osprey Publishing, 1997. ISBN 1-85532-529-2.
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- Sakurai, Takashi. Hien Fighter Group: A Pictorial History of the 244th Sentai, Tokyo's Defenders (in Japanese/English). Tokyo, Japan: Dai Nippon Kaga, 2004. ISBN unknown.
- Takaki, Koji and Sakaida, Henry. B-29 Hunters of the JAAF. Botley, Oxford, UK: Osprey Publishing, 2001. ISBN 1-84176-161-3
- Tanimura, Masami; Tanaka, Kozo; Kishida, Yuji; Oda, Makoto; Nakano, Yoshiharu and Kawasaki, Saburo. Kawasaki Ki-61 (Tony). Blaine, WA: Paul Gaudette, Publisher, 1967.
- Vaccari, Pier Francesco. "Guerra Aerea in Nuova Guinea" (in Italian). Rivista Italiana Difesa, N.8, 2000.

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