Kawasaki Ki-61

infobox Aircraft
name = Ki-61 "Hien"
type = Fighter
manufacturer = Kawasaki Aircraft
(Kawasaki Heavy Industries)

---

caption = A Ki-61 -I -"Otsu"
designer = Takeo Doi and Shin Owada
first flight = December 1941
introduced = 1943
retired = 1945
status =
primary user = IJA Air Force
more users = Chinese Nationalist Air Force
produced =
number built =3,159
unit cost =
variants with their own articles = Kawasaki Ki-100

The Kawasaki Ki-61 "Hien" (飛燕, 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" (三式戦闘機). [ Mondey 2006, p. 144.] It was the only mass-produced Japanese fighter of the war to use a liquid-cooled inline "V" engine.

Design and development

The Ki-61 which was designed by Takeo Doi and his deputy Shin Owada, was one of two parallel designs tendered for by Kawasaki to fulfill requirements framed by 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 [Note: The Nakajima Ki-44 was selected as the standard IJAAF interceptor fighter and followed broadly similar specifications to the Ki-60.] ; 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 [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.] . Both single-seat, single-engine fighters used the same basic construction being 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. Green and Swanborough, 1976, pp. 18-23]

The all metal, semi-monocoque fuselage was basically oval in cross-section, changing to a tapered, semi-triangular oval behind the cockpit, with a maximum depth of 1.35 m (4 feet 5 inches). 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 the top and bottom cowling panels only 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 caliber 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) 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 (36.2 Imp gallons) was located behind the pilot's seat. The windshield was armoured and there was a 13 mm armoured steel 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.

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 partially self-sealing 190 l (42 gallon) 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. 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 (6,504 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). [Green and Swanborough 1976, p. 23.]

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. Francillon 1966, p. 319.] [ Green 1975, p. 78.] [Francillon, 1979, p. 114.] [Green and Swanborough 1976, p. 23.]

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 1,500 hp inline or 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. Vaccari 2000, pp. 82–90.]

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) 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.

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, Hyōgo, 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.

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". Francillon 1966, p. 316.] [ Crosby 2002, p. 94.]

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.Vaccari 2000, pp. 82–90.]

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, 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 After the Japanese retreat, over 340 aircraft wrecks were later found at Hollandia.

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. [Francillon, Dr. Réne J. "Japanese Aircraft of The Pacific War" (2nd ed.), Naval Institute Press 1979.]

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. Of the allied fighters encountered at the beginning of World War II, only the P-38 was measurably superior. [Green and Swanborough 1976, p. 29.] 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. Gibertini 1998, pp. 6-13.]

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 kt) 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 machine guns. The empty and maximum weights for the Ki-61 prototype (2 x 12.7 mm + 2 x 7.7 mm) were 2,238 kg (4,934 lb) and 2,950 kg (6,504 lb), respectively; for the Ki-61-I basic (4 x 12.7 mm) 3,130 kg (6,900 lb); and for the Ki-61-KAI (2 x 12.7 mm + 2 x 20 mm), 2,630 kg (5,798 lb) and 3,470 kg (6,750 lb).

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. [Green and Swanborough 1976, pp. 27-28.]

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. [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.] [ [http://home.att.net/~sallyann6/b29/56years-4408.html Pacific War Chronology; August 1944] Retrieved: 12 June 2008] Other attacks of this nature followed, as a result of which individual pilots determined it was a quite practical way to destroy B-29s. [Takaki 2001.]

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. [ [http://wgordon.web.wesleyan.edu/kamikaze/books/general/takaki/index.htm Webpage on Kamikaze from Japanese and American perspectives] Retrieved: 12 April 2008]

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 Lt. 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.) [Sakaida 1997, pp. 67-70] [ [http://www.xavierb.net/japan/bukosho.htm Bukosho described] Retrieved: 3 June 2008] 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. [ [http://www.tokkotai.or.jp/ Japanese website dedicated to the "Tokkotai" JAAF and JNAF] Retrieved: 7 June 2008]

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. [Sakaida 1997, pp. 74-75.]

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.

Source: Sakaida, Henry. "Japanese Army Air Force Aces 1937-45". [Sakaida 1997, pp. 82-87.] Bueschel, Richard M. "Kawasaki Ki.61/Ki.100 Hien in Japanese Army Air Force Service". [Bueschel 1971, pp. 47-49.]

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 tail wheel and two 2 x 7.7 mm (0.303 in) Type 89 machine guns in the wings and two synchronized 2 x 12.7 mm (0.50 in) Ho-103 machine guns in the fuselage forward decking. The wings had racks outboard of the wheelbays, which were capable of carrying one 40 gallon drop tank or a light bomb.;Ki-61-I-"Otsu":The second production fighter variant. As it was found the armament was too light against allied aircraft and the tail wheel retraction mechanism was unreliable, the plane was modified accordingly. Two 12.7 mm Ho-103 heavy machine guns replaced the wing 7.7 mm machine guns, with modifications to the upper-wing bulges, and the tail wheel well doors were removed and the tailwheel locked in the "down" position (although the mechanism was still intact).;Ki-61-I-"Hei":800 German made Mauser MG 151/20, 20 mm 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. 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. [ [http://www.markkaiser.com/japaneseaviation/hien.html Ki-61 survey] Retrieved: 11 June 2008] ;Ki-61-I-"Tei":This machine featured two 12.7mm 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 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. [ Mondey 2006, p. 146.] ;Ki-61-I-KAId:Interceptor variant with 2 x 12.7 mm fuselage machine guns and 2 x 30 mm 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 630km/hr (395 m.p.h.), 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 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. [ [http://www.faqs.org/docs/air/avhien.html "The Kawasaki Ki-61 Hien ("Tony") & Ki-100".] Retrieved: 20 February 2007.]

Operators

;China as ROC
*Chinese Nationalist Air ForceOperated some captured aircraft;CHN
*People's Liberation Army Air ForceAlso operated some captured aircraft;flag|Indonesia
*In 1945, Indonesian People's Security Force (IPSF) (Indonesian pro-independence guerrillas) captured a small number of aircraft at numerous Japanese air bases, including Bugis Air Base in Malang (repatriated 18 September 1945). Most aircraft were destroyed in military conflicts between the Netherlands and the newly proclaimed-Republic of Indonesia during the Indonesian National Revolution of 1945–1949. [ [http://nei.adf-serials.com/indonesian-aviation-1945-50.pdf Indonesian aviation 1945 -1950] ] ;JPN
*Imperial Japanese Army Air Force

pecifications (Ki-61-I-KAIc)

aircraft specification

plane or copter?=plane
jet or prop?=prop
ref=The Great Book of Fighters [ Green, William and Swanborough, Gordon." The Great Book of Fighters". St. Paul, Minnesota: MBI Publishing, 2001. ISBN 0-7603-1194-3.]
crew=One
length main=8.94 m
length alt= 29 ft 4 in
span main=12.00 m
span alt=39 ft 4 in
height main=3.70 m
height alt=12 ft 2 in
area main=20.00 m²
area alt=215.28 ft²
empty weight main=2,630 kg
empty weight alt=5,800 lb
loaded weight main=3,470 kg
loaded weight alt=7,650 lb
max takeoff weight main=
max takeoff weight alt=
more general=
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
engine (prop)=Kawasaki Ha-40
type of prop=liquid-cooled inverted V-12
number of props=1
power main=875 kW
power alt=1,175 hp
max speed main=580 km/h
max speed alt=360 mph
max speed more=at 5,000 m (16,405 ft)
range main=580 km
range alt=360 mi
ceiling main=11,600 m
ceiling alt=38,100 ft
climb rate main=15.2 m/s
climb rate alt=2,983 ft/min
loading main=173.5 kg/m²
loading alt=35.5 lb/ft²
power/mass main=0.25 kW/kg
power/mass alt=0.15 hp/lb
more performance=

Time to altitude: 7.0 min to 5,000 m (16,405 ft)
armament=
* 2x 20 mm Ho-5 cannon, 120 rounds/gun
* 2x 12.7 mm (0.50 in) Ho-103 machine guns, 200 rounds/gun
* 2x 250 kg (550 lb) bombs

ee also

aircontent
related=
* Kawasaki Ki-60
* Kawasaki Ki-100

similar aircraft=
* Heinkel He 100
* Macchi C.202
* Messerschmitt Bf 109
* LaGG-3

lists=
* List of military aircraft of Japan

References

Notes

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.
* Hata, Ikuhiko, Izawa, Yasuho and Shores, Christopher. "Japanese Army Air Force Fighter Units and Their Aces, 1931-1945". London: Grub Street Publishing, 2002. ISBN 1-902304-89-2.
* 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). Gdańsk, 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.
* Sakurai, Takashi. "Rikugun Hiko Dai 244 Sentai Shi" (History of the Army 244 Group) (in Japanese). Tokyo, Japan: Soubunsha, 1995. ISBN unknown.
* 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.

External links

* [http://www.vectorsite.net/avhien.html KI-61 article on vectorsite (public domain)]
* [http://www.j-aircraft.com/research/jimlong/tony/tony.htm Article on Ki-61-II-Kai production No.5017, still in existence] Retrieved: 7 June 2008.
* [http://www.j-aircraft.com/captured/testedby/me109/me109.htm Japanese aircraft]
* [http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf USN report on captured Ki-61 (pdf file)] Retrieved: 11 April 2008
* [http://wgordon.web.wesleyan.edu/kamikaze/index.htm Website on Kamikaze from Japanese and American perspectives] Retrieved: 12 April 2008
* [http://www.tokkotai.or.jp/ Japanese website dedicated to the "Tokkotai" JAAF and JNAF] Retrieved: 7 June 2008