The Japanese fighter the Allies mistook for a European one

What makes it special

Full specifications

Figures below are for the Ki-61-II-KAI, the late-war Ha-140 version; early Ki-61-I aircraft were a little lighter and slower. Wartime Japanese figures vary between sources, so some values are commonly-cited approximations.

Baseline note: the figures below describe the Kawasaki Ki-61-I-Tei — the Army Type 3 Fighter, Model 1d — built at Gifu between January 1944 and January 1945 and, at 1,358 aircraft, by a wide margin the most numerous mark. It is also the fairest baseline, because it is the version most Allied pilots met. Deltas for the lighter Ki-61-I-Otsu and for the Ha-140-engined Ki-61-II-KAI are given in grey. Japanese manufacturer’s figures for the Hien survive in several competing sets; where Akimoto’s 1961 tabulation, Watanabe’s reconstruction and René Francillon’s English-language account disagree, the disagreement is stated rather than averaged away.

Armament & payload

The Hien fought its best battles with German cannon it could not replace, and its worst with Japanese ones it could not get

Armament is the clearest single thread through the Ki-61’s five years, because the Japanese Army began the war without an aircraft cannon and spent the rest of it improvising. The first Hien carried two synchronised 12.7 mm Ho-103 in the decking and two rifle-calibre Type 89 machine guns in the wings, which was inadequate against a B-17 and merely adequate against a P-40. The answer, from late 1943, was 800 Mauser MG 151/20 cannon bought from Germany and shipped to Japan by submarine: superb weapons, fitted to the Ki-61-I-Hei, and impossible to resupply once the ammunition ran out, so that units sent to the Philippines had them taken out again before they left. Only in 1944 did the home-grown 20 mm Ho-5 arrive, and fitting it meant six months of work on a synchronisation gear for a cannon — something the Imperial Navy flatly refused to attempt, on the grounds that a 20 mm round detonating in the propeller disc would take the blade off. Ammunition capacities are reported inconsistently across marks, and the figures below take the most commonly attested value for each; where a source disagrees materially, it is named.

Sourcing caveat. Japanese ordnance returns for 1943–45 are fragmentary, and much of what circulates in English traces to Francillon’s 1970 reconstruction or to post-war interrogation. Per-gun ammunition loads, the extent of field conversion between marks, and the true number of 30 mm-armed aircraft are all reported inconsistently; the more conservative figure has been taken throughout, and claims of aircraft destroyed are given as claims.

Variants

Four gun fits, one failed engine and 275 finished airframes with nothing in the nose

Takeo Doi and his deputy Shin Owada drew the Ki-61 from December 1940 against a Koku Hombu requirement for two fighters built around the Daimler-Benz DB 601Aa. The other, the Ki-60, was the heavy interceptor and flew first; the Ki-61 was to be the lighter general-purpose machine. Doi refused the Army’s doctrinal split between light and heavy fighters altogether and called what he was building a "medium" fighter, a decision he traced back to losing the 1939 competition with the fast but stiff-turning Ki-28. The result first flew at Kagamigahara in December 1941, reached 590 km/h in comparative trials against a Ki-43, a Ki-44, a defector’s LaGG-3, a Bf 109E-7 and a captured P-40E, and beat every one of them for speed. Only the Ki-43 out-turned it.

The aeroplane was good. The engine was the problem, and it was never solved. The Ha-40 was some 30 kg lighter than the DB 601Aa it copied, which meant it demanded tolerances the German engine did not, from an industry that could not hold the German ones. The Army instructed Kawasaki to leave nickel out of the chrome-molybdenum steel; crankshafts developed surface cracks and broke. Roller bearings measured from a surviving Ha-40 in 1998 showed a roundness of 0.010 to 0.022 mm where SKF held 0.001 mm. Cylinder yield ran at about 50 per cent. Bosch would not licence the fuel-injection patent. One Japanese history of the Diesel Kiki works puts the acceptance rate of injection pumps at 5 per cent. The engine took three times the manufacturing steps of an ordinary 1,000 hp radial; the Ha-140 that followed took five. From the autumn of 1944, complete Ki-61 airframes began accumulating at Gifu with no engine to fit — 190 of them by that November, before the Ki-61-II programme had even properly started.

Then it got worse. Ha-140 deliveries against a schedule of 20 engines in July 1944 came to 8; 40 were due in August and 5 arrived; September produced a single engine. Captain Tomoo Natori of the Army Air Inspection Department, sent to live at the Akashi works and find out why, concluded that as an engineer he could not tell anybody to fly behind one. B-29s destroyed the Akashi plant on 19 January 1945 and settled the argument. Of 374 Ki-61-II-KAI airframes completed, 99 received engines, of which bombing and attrition left about 60 delivered and 52 issued to the 55th and 56th Sentai. The remaining 275 stood headless, and became the Kawasaki Ki-100 — a conversion covered in full on its own page in this encyclopedia, and not repeated here.

Ki-61 prototypes (Dec 1941–1942, 12)

Three prototypes and nine pre-production aircraft. The first three are stated by the Army test pilots who flew them to have used imported DB 601Aa engines; the Ha-40 appeared from the fourth aircraft and brought supercharger trouble with it. Two were scrambled against the Doolittle B-25s on 18 April 1942 carrying practice armour-piercing rounds, and hit one to no effect.

Ki-61-I-Ko, Army Type 3 Fighter Model 1a (Aug 1942–Sep 1943, 388)

First production version, airframe numbers 113 to 500. Two 12.7 mm Ho-103 in the decking, two 7.7 mm Type 89 in the wings, fully retractable tailwheel. Self-sealing tanks and pilot armour from the start, which no other Japanese fighter of 1942 could claim.

Ki-61-I-Otsu, Model 1b (Sep 1943–Apr 1944, about 592–603)

Wing guns raised to 12.7 mm; the unreliable retracting tailwheel fixed down. A troublesome fuselage tank was deleted from the 514th airframe after it was blamed for crashes just after take-off, and added armour above the radiator went in at the same point. The fastest-climbing mark the type ever had.

Ki-61-I-Hei, Model 1c (Sep 1943–Jul 1944, about 388)

Wing guns replaced by imported Mauser MG 151/20, barrels protruding from the leading edge. Kawasaki called it the "Ki-61 Ma-shiki". Eight hundred guns and 400,000 rounds arrived against a contract for 300 a month, because the only route left was by submarine. Whether the 388 figure includes field conversions of earlier marks is disputed: Komine counts 387 built new and no conversions, Ikari 235 new plus a hundred-odd converted.

Ki-61-I-Tei, Model 1d (Jan 1944–Jan 1945, 1,358)

The definitive Hien and the most-built. Two 20 mm Ho-5 moved into a nose lengthened by about 200 mm, with a synchronisation gear developed over six months, thicker nose skinning against premature shell detonation, tail ballast and the wing shifted 4 cm forward to hold the centre of gravity. It gained 250 kg empty and lost 30 km/h and a minute and a half of climb for it. A few were rebuilt with 30 mm Ho-155 wing cannon for B-29 interception.

Ki-61-I evaporative-cooling testbed (experimental, very few)

Surface evaporative cooling on the Heinkel He 100 principle, deleting the ventral radiator altogether. It reached 630 km/h (391 mph), the fastest Hien ever flown, and was as impractical in Japanese hands as it had been in German ones.

Ki-61-II (Aug 1943–Jan 1944, 8)

The Ha-140 installation with an enlarged 22 m² wing sized to take Ho-5 cannon internally, a 420 mm fuselage stretch, a bigger fin and a radiator core lengthened from 250 to 300 mm for 20 per cent more cooling. Water-pump failures wrecked the test programme; handling disappointed; the eighth aircraft was still beginning engine flight tests in June 1944, and the design was abandoned.

Ki-61-II-KAI, Army Type 3 Fighter Model 2 (Sep 1944–1945, 374 airframes, 99 engined)

The Ki-61-II reworked around the Tei’s 20 m² wing and its armament, 220 mm longer than a Tei with the wing moved 8 cm forward. When the engine ran it was a genuinely good aeroplane: 610 km/h, comfortable formation flying at 10,000 m, out-diving even the Ki-84 and Ki-100 in Akeno trials, and rated by the 55th Sentai as no worse than a P-51 on equal terms. It almost never ran.

Ki-61-III (1945, 1 prototype)

Cut-down rear fuselage with an all-round-vision canopy. The airframe went nowhere, but the canopy did: it reappeared on the Ki-100-I-Otsu, the only part of the Hien’s last development to see production.

Export, licence production and post-war users (none exported; three post-war operators)

There was no export and no licence production; the Hien never left Japanese service while Japan was fighting. Afterwards, captured examples were flown briefly by the Chinese Nationalist air force and the People’s Liberation Army Air Force, and six were taken over in 1945 by Indonesian republican forces, most of which were destroyed during the national revolution of 1945–49.

Production and survivors, counted carefully. The figure of 3,159 aircraft circulates widely and should be treated with caution. The United States Strategic Bombing Survey’s monthly returns give 3,058 — 2,654 Ki-61-I and 404 Ki-61-II — and Francillon gives 3,078, comprising 2,666 and 412 including prototypes; Japanese authorities put the range at 3,148 to 3,162, which is where 3,159 comes from. Whichever total is preferred, 275 of those airframes never flew as Hien at all, becoming Ki-100s instead, so roughly 2,875 aircraft served as Ki-61s. Exactly one complete original survives anywhere in the world, and it is in Japan: Ki-61-II-KAI, Kawasaki construction number 6117, the seventeenth Model 2 built at the Gifu works in 1944. It served with the Army Air Inspection Department, was seized by American forces at Fussa immediately after the surrender and later passed to the Japan Aeronautic Association. It was shown at a Keio department store war exhibition in 1965, spent 23 years in store at the JASDF Gifu base, and was lent from 1986 to the Chiran Peace Museum in Kagoshima. Removed in September 2015, it was stripped and restored by Kawasaki Heavy Industries at Gifu across 2015 and 2016, exhibited at Kobe, and has been on display in the main hall of the Gifu-Kakamigahara Air and Space Museum since 24 March 2018. The restoration settled its identity: stencil traces found under the paint proved the construction number to be 6117, not the 5017 or 61217 previously assumed. Three further original airframes exist as incomplete recovered wrecks, all from New Guinea — number 299 under static restoration for the Papua New Guinea National Museum, number 640 under restoration towards airworthy condition for the Military Aviation Museum at Virginia Beach, both worked on by specialist shops in Australia and New Zealand, and number 379 in storage at Fantasy of Flight in Polk City, Florida. There is no flying example. A full-size replica, built to measurements taken from a New Guinea wreck bought at auction in 2017 by a Kurashiki businessman, was unveiled at Ibaraki Airport on 9 September 2023 and has been displayed at Asakuchi in Okayama since April 2024; it is a reproduction and is counted as one here. Wrecks remain scattered across the Pacific, including an airframe photographed on the seabed of Cenderawasih Bay.

From a German licence to a radial-engined rescue

From the war: twelve Hien stories

The Hien in pictures

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The Hien on film

Verified archival footage of the Kawasaki Ki-61 Hien in flight is scarce, and we would rather show you nothing than something mislabelled. A carefully sourced video is coming soon.

Where the Hien flew

The record that defines it

The Hien was a workmanlike frontline fighter rather than a record-setter, and precise Japanese victory tallies are unreliable. Its significance lies in what it represented: the one Japanese Army fighter with a European inline engine, armour and self-sealing tanks, effective enough at altitude to be trusted with the defence of Japan itself — and hamstrung less by the enemy than by the engine its own industry could not build.

Compare the combat record of every military aircraft. Figures as of July 2026.

Everything people ask about the Ki-61 Hien

Continue the tour

Every fact, checked

• The History of War — Kawasaki Ki-61 HienJ. Rickard’s detailed development and service history, and the “Tony” naming.
• Air Vectors — The Kawasaki Ki-61 & Ki-100Greg Goebel’s technical overview of the Ha-40 engine and the radial-engined Ki-100.
• Pacific War Online Encyclopedia — Ki-61 “Tony”Kent Budge’s reference specifications and combat summary.
• World War II Database — Ki-61 HienCross-check for dimensions, weights and armament figures.
• Military Factory — Kawasaki Ki-61 Hien (Tony)Variant breakdown and production overview.
• Smithsonian National Air and Space MuseumReference for Japanese wartime aircraft and preservation context.