Supermarine Spitfire Vb vs. Kawasaki Ki-61-I-KAIc Hien (“Tony”)

Spit V Ki-61

The alliance between Germany and Japan has been the subject of much debate since the end of World War II. Theoretically, neither nation should have considered the other a viable ally because of their own similar concepts of their own racial superiority that considered the other inferior. However, given the geographical distances between them their own immediate interests were unlikely to clash at least for the foreseeable future. One thing they both had in common was the possibility of clashing with the British Empire; Germany on mainland Europe against Britain herself while Japan against her Eastern possessions. Despite this it was actually the threat from the Soviet Union to both parties that laid the groundwork for the formalising of an alliance in the shape of the Anti-Comintern Pact. When Italy signed on to the treaty the Axis powers were created.

When the Axis powers finally found themselves thrust in to war with Britain, the USA and the Soviet Union they effectively fought two separate conflicts. There was very little coordination between them in the same way that there was between the Allied nations but both sides of the Axis compass knew of the importance of keeping the other’s fight alive because the defeat of one would only see the Allies relocate the resources fighting the defeated nation brought to bare on them and this is exactly what happened after Germany and Italy fell in 1945. To that end there was a lot of technology exchange between them with Nazi Germany going to great lengths to get scientists and technology to Japan hoping they could put them to good use to perhaps ease the pressure in Europe. This was especially true in military aviation and in turn led to the development of the Kawasaki Ki-61 Hien – a fighter that would not look out of place over the skies of Europe.

Kawasaki Ki-10

Kawasaki Ki-10

The story of the Ki-61 can be traced back to the appointment of German engineer Dr. Richard Vogt to the position of chief designer at the Kawasaki Aircraft Engineering Company between 1923 and 1933. During his time at the company he impressed many Western design philosophies on the aircraft he worked on and this left a great impression on his Japanese successor Takeo Dai. One of Vogt’s biggest influences on Takeo Dai and Kawasaki was the belief in liquid-cooled inline engines as opposed to the air-cooed radial designs that prevailed in Japan at that time. This relatively radical approach produced the Ki-10 biplane fighter powered by a license built BMW inline engine but these aircraft remained the exception.

Advances in Europe with such engines couldn’t be ignored forever and in 1935 the British flew the prototype for what would become the Hawker Hurricane for the first time while Germany flew the Messerschmitt Bf109 prototype a year later. Both of these aircraft were fitted with inline engines which gave them performance far in advance of the many radial-engined aircraft then in Japanese service. This resulted in Japanese interest in the Bf109 and plans for an acquisition reached an advanced stage before being cancelled. While they were impressed with the Messerschmitt design they disliked the short range of the aircraft which didn’t meet their requirements for an offensive fighter. They were however impressed with the aircraft’s Daimler-Benz DB 601A engine and so plans were made for a license produced version to be built in Japan and fitted to a Japanese designed aircraft that could meet the Imperial Japanese Army’s requirement for an offensive fighter.

In 1939 the Japanese aviation bureau, the Koku Hombu, issued a requirement for two aircraft to be built around the new engine. The first was to be a high altitude interceptor while the second was to be a general purpose offensive fighter. Takeo Dai went about designing the Ki-60 and Ki-61 respective to these requirements but ultimately the Ki-60 was dropped. Development of the Ki-61 continued but the first flight didn’t take place until December 1941 by which time the engine was falling behind its competitors in the West.

Macchi C.202

Macchi C.202

Even before the aircraft flew Britain’s Royal Air Force began receiving the latest Spitfire, the Mark V, which was designed to address some of the shortcomings of the earlier Spitfires such as Mark I/II. Unfortunately the Mark V will always be remembered as being too little too late for its arrival coincided with the arrival of the “Butcher Bird” – the mighty Focke-Wulf Fw190 over Europe. While it was a poor match for the Fw190 it was still a good aircraft comparable to nearly all other fighters in the European and North African theatres including the Messerschmitt Bf109E  and Macchi C.202 (see comparison here) both of which used the DB 601 engine. The similarity of the Ki-61 to the C.202 was such that Allied pilots actually initially mistook it for the Italian fighter and this in turn resulted in it receiving the Allied codename of “Tony” based on the Italian name “Antonio”.

Early combat experience with the Ki-61 revealed that it was still underdeveloped despite being an improvement over previous Japanese designs that it was replacing. This was especially true in terms of its armament and the designers at Kawasaki went back to the drawing board producing a slightly longer variant with a heavier punch. This “new” aircraft was designated as the Ki-61-I KAIc.

In a fight between the Supermarine Spitfire V and the Kawasaki Ki-61-I KAIc which aircraft had more going for it?


Spitfire Vb

The Spitfire V was powered by a Rolls-Royce Merlin 45, a variant of the Merlin XX and came fitted with a single-stage, single-speed supercharger. The engine still lacked the direct fuel injection system of the German engines but improvements to the carburettor did allowed the Spitfire V to undertake negative-G manoeuvres without major disruption to the flow of fuel as had been the case in earlier variants. First production Merlin 45s were delivered in January 1941 and churned out around 1,450hp at 9,000ft, an advance over the Spitfire II/Merlin XII combination of some 275hp, which it translated it in to forward motion via a three bladed propeller.

Despite these advances the Merlin 45 proved problematic in the Pacific theatre. The Royal Australian Air Force found quite quickly that the Spitfire V was a logistical headache in the extreme since the parts for it were built half way around the world. The dust and heat of the outback of Northern Australia was particularly hostile to the Merlin where it went from extreme heat on the ground to extreme cold at high altitude causing numerous breakdowns and leakages thus further straining the logistical chain supporting it.

Kawasaki Ki-61 4

It would be more accurate to say that the Kawasaki Ha-40 engine was a development of the DB 601A rather than a direct license produced version as was the case with the Macchi C.202’s  RA.1000 R.C.41-I Monsone version. While the engine had the same layout and configuration as the DB 601 it was tweaked slightly to better meet Japan’s requirements. Consequently the Ha-40 offered more power at take-off than the DB 601A and was actually marginally lighter. The engine was delayed briefly which meant that the first three Ki-61 prototypes flew with DB 601A engines provided by Germany before the first Ha-40s became available.

Even before the constraints of war with America the engine suffered chronic reliability problems compared to the more reliable DB 601A as a result of infrequent manufacturing practices at the Akashi plant where it was built. The situation was only exacerbated by the intervention of the US Navy’s submarine blockade of the Japanese home islands meaning that production of later Ha-40 engines was often undertaken with sub-par materials sourced in Japan rather than the high quality materials imported from the Asian continent. When functioning properly the Ha-40 produced 1,159hp which turned a three bladed propeller.


Spitfire VB Trop 2

The Merlin 45 pulled the Spitfire Vb along at a comfortable top speed of 375mph at 20,000ft. The dust encountered at lower levels such as during take off or straffing enemy formations required the fitting of a large Vokes air filter that not only ruined the Spitfire’s elegant lines but also incurred a 7-9mph speed penalty. The aircraft had an initial climb rate of 2,600ft/min which increased to over 3,100ft/min above 14,000ft once clear of the thicker air lower down leading on to a service ceiling of 36,500ft. The Spitfire Vb had a respectable wing loading of 27.35 lb/ft2  and had a maximum of 639hp to share for every ton in weight while with a full fuel and weapon loadout this figure fell to 490hp per ton.

Kawasaki Ki-61

The Ki-61 topped out it’s air speed indicator at 367mph at 16,400ft which was still a good figure for the period given that more powerful engines were available by the time the Ki-61 was entering service after its protracted development. It was capable of reaching a service ceiling of just over 38,000ft and had an initial rate of climb of 2,983ft/min which increased around 16,000ft before dropping off again. The Ki-61 had a higher wing loading than most of the contemporary Japanese designs again betraying its Western influence being in the region of 35.5 lb/ft² which was even higher than the Spitfire Vb. With the Ha-40 installation the Ki-61 had a maximum power to weight ratio of 440hp for every ton. When flying under a full load however this ratio dropped to just 330hp per ton.


Spitfire Vb 2

It’s name may have been “Spitfire” but in the early marks, Supermarine’s legendary fighter was barely an adequate gun platform. It’s eight .303 machine guns were spaced out across the wing making it difficult to train them to a point ahead of the aircraft where their collective firepower could inflict heavy enough damage on an enemy aircraft equipped with self sealing fuel tanks and armour. This was why the Hawker Hurricane, with its eight .303 machine guns coupled closely together, was the superior gun platform in the Battle of Britain.

Efforts were therefore made to up-gun the Spitfire by fitting 20mm cannons but early trials were abysmal with the Hispano 20mm cannon proving extremely unreliable and prone to jamming after just a few shots. Nevertheless the RAF persisted and after the bugs had been ironed out cannon armament became the standard on all later Spitfires. The Spitfire Vb was therefore armed with a pair of 20mm cannon each with 60 rounds and these had a muzzle velocity of 2800ft/sec. The .303s were still there however and the Spitfire Vb carried four of them spaced along the wings. There were alternative wing configurations available and some variants of the Mark V were armed with four 20mm cannon mainly in the light attack mission but this didn’t become standard for fighter variants until the last two years of the war.

Kawasaki ki-61 guns

The early Ki-61s too suffered from light armament. The early production versions were armed with two 7.7mm (0.303in) Type 89 machine guns in the wings and two synchronized 12.7 mm (0.50 in) Ho-103 machine guns in the upper engine cowling in a similar arrangement to the Messerschmitt Bf109 and Macchi C.202/205. This proved inadequate against the sturdy American bombers such as the B-17 Flying Fortress and so the Japanese began a series of efforts to up-gun the aircraft including at one point the fitting of German Mauser MG 151/20 cannons brought to Japan by U-Boat.

By the time the Ki-61-I-KAIc appeared the Japanese had settled on having two Ho-5 20mm canon mounted in the forward fuselage position synchronised to fire through the propeller. The Ho-5 was developed from the Ho-103 machine gun which was itself developed from the American Model 1921 Browning aircraft machine gun and as such used belt-fed ammunition that utilised Browning-style steel disintegrating links between the rounds. Each gun was given 120 rounds and these could be discharged at 2,460 ft/s with a rate of fire of 950rds/min.

The wings featured a pair of 12.7 (.50cal) Ho-103 machine guns that each was given a generous 250 rounds each. The weapon could fire put these rounds on to a target at 2,600 ft/s with a rate of fire being 900rds/min. As the war progressed some aircraft saw these weapons replaced by another pair of Ho.5s finally giving the Ki-61 the heavy punch it always needed.


Supermarine Spitfire V 6

The Spitfire pilot sat sandwiched between two fuel tanks; one ahead of the cockpit behind the Merlin engine and an auxiliary tank behind the cockpit. This meant that should his aircraft be hit in either of these areas he was likely to suffer horrendous burns if he didn’t get out quick enough. To that end Martin-Baker, the company that would eventually become synonymous with ejection seat technology, developed a quick release system that allowed the Spitfire pilot get the canopy off in one quick movement and allow him to exit. The fuel tanks featured a rubber self-sealing system that expanded over single small calibre bullet holes but was rendered ineffective if there was a number of impacts.

He was not entirely without protection as he had armour plates behind his seat and head as well as a bullet-resistant windscreen. While the Spitfire was often cited as a delight to fly it was a notoriously bad aircraft to handle on the ground thanks to its narrow undercarriage that raised from the centre fuselage towards the wingtips as opposed to the opposite which was much more common and much more stable on semi-prepared airstrips as was often the case in the Pacific and the China-Burma-India theatres.

Kawasaki Ki-61 2

The pilot of the Ki-61 sat ahead of the fuselage fuel tank while ahead of him was the ammunition feed and storage tank for the cowling mounted weapons. This provided some additional level of protection to the pilot from an attack from the forward hemisphere such as when facing defensive guns on a bomber. This was because there was a lot of objects to get in the way of the bullet reducing how far it could travel through the aircraft. The Ki-61 was one of the first Japanese aircraft to feature self-sealing fuel tanks making it more resilient than many other Japanese aircraft of the period.

The aircraft was more robust than the Spitfire being of solid construction and having a wider set landing gear making it far more stable on the ground. It also made it far more likely for the pilot to walk away from a hard landing such as when occurs after taking heavy damage. The narrower wing positioned more centrally to the pilot as opposed to the Spitfire meant that he did enjoy a greater field of downward view fore and aft although both aircraft had poor rearward vision.


Both of these aircraft enjoyed very brief periods of superiority over their contemporaries before new models rendered them obsolete. Compared to one another they are quite well matched in many respects but each have their own strengths and weaknesses. The Ki-61-I-KAIc pilot enjoyed a certain degree of superiority in performance at lower levels where his aircraft had a speed and climb advantage. Between 15,000 and 20,000ft the two aircraft become more evenly matched while above these altitudes the Spitfire V began to enjoy a greater degree of performance thanks mainly to its larger wing area that produced more lift and the fact the Rolls Royce Merlin was tailored for this flight regime. This is despite the fact that the Ki-61-I-KAIc enjoyed a very slight advantage in terms of service ceiling.

In terms of agility the larger wing area of the Spitfire meant that the aircraft’s rate of roll, especially lower down in the denser air, was behind that of Ki-61-I-KAIc. It did however aid in the aircraft achieving a very high rate of continuous turn and with a higher power-to-weight ratio the Spitfire was therefore more agile in the horizontal plane than the Ki-61-I-KAIc. If attacked the Spitfire pilot’s best defence would be to try to keep turning ahead of the Ki-61 pilot’s arc of fire.

Regarding firepower, even though the Spitfire technically had more guns, the larger calibre of the wing mounted machine guns in the Ki-61-I-KAIc helped negate this advantage somewhat which means that in terms of damaging an enemy aircraft the two aircraft’s effectiveness was broadly the same although with more bullets flying the Spitfire at least had a higher chance of hitting something.

In this instance there is no clear winner as the altitude at which the combat would take place would have a major impact on the aircraft. As always we also have to take in to consideration pilot capability and in this respect the quality of Japanese pilots diminished as the war went on and their situation became more desperate. Another important factor to consider is that the Spitfire Vb was never considered ideally suited for operations against the Japanese given the environment they were expected to operate in that played havoc with it. The Spitfire VIII however was a far superior aircraft and enjoyed far more success against the Japanese although The Spitfire Vs did soldier on until the end of the war in an increasingly diminishing capacity.


17 responses to “Supermarine Spitfire Vb vs. Kawasaki Ki-61-I-KAIc Hien (“Tony”)

  1. Pingback: Defence of the Realm – Technology | Defence of the Realm

  2. I think the bottom line is that both aircraft were very equally matched. Its interesting that even their worst shortcomings were similar; that is, maintenance intensive engines that struggled at remote bases at the end of a long supply chain. The Ha-40 engine worked well enough at major bases in Japan, but proved troublesome when deployed to Sumatra or New Guinea. Just like the Merlin could be difficult in Darwin.

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  3. The alliance between the Axis and Japan was hardly an obvious one in so many respects – an example of expedience rather than anything else. Still, it was this that led to New Zealand being targeted by Japanese war planners, at the urging in 1940 of von Ribbentrop. I’ve seen the occupation plans they prepared – held now by Archives New Zealand.

    It’s intriguing how similar the ‘Spit’ and the ‘Tony’ were in so many ways – instances, I guess, of the fact that the technologies of the major industrial powers of the day were broadly also similar in many respects.


    • The occupation plans for a lot of countries were frightening. I used to work at the St Fagan’s museum where the main manor house, we found out recently, was listed by the Germans as a base of operations for the occupation of south east Wales.

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  5. The Ki-61 lacked essentially a good sight outside the aircraft, and a reliable engine as the japan version was lighter than the already delicate DB-601. Put to it the original german made stuff and it will be easily the best DB-601 fighter, with a lot more range and firepower than the MC.202 and more of all vs the Bf-109E/F.


  6. The Tony had better dive limit.
    The cowl 20mm cannons were slowed by half but we’re not limited by convergence range like the Spitfire’s wing cannons. So it was more lethal long range and had more ammo. The Spit tended to spin out in a very tight turn so stall was to be avoided against Japan.
    The biggest weakness of the Spit V was short range in the Pacific. This gives the Tony a stacked deck.
    The biggest weakness of the Tony was the unreliable engine.
    So it would be dicey for both sides.

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  7. An interesting ‘what if?’ scenario would be a Tony fighter with it’s best solutions applied.

    1. What if it’s inline engine was beefed up in the right places like the original DB 601 was, instead of making it lighter? This engine was not the right place to cut weight.
    If ball-bearings were a problem in Japan, use slider bearings like the Italians did in their Fiat version of the DB 605 engine, if I’m not mistaken. Result: a more reliable inline engine than the Kawasaki Ha-140 engine equivalent for the high flying Ki 61-II.

    2. The Bf 109G had a hub motor cannon, the Fiat G.55 and Yak did too. Why not the 1944 Ki 61-II?
    In 1944 Japan had arguably the best 37mm cannon in the Ho-204. This was lethal enough to stop B-29s! That is why the Dinah and Randy twin engined fighters had it.
    The inline Ki 61 was the only single engined Japanese fighter that could mount this as a motor cannon in the hub. It would be better than the successful Yak-9T.
    The Ki 61-II was potentially the best high altitude B-29 interceptor.
    The Yak-9T was not even close to being a high altitude fighter.
    It’s NS-37 cannon was heavier and much slower at 250 r/m than the 400 r/m 37mm Ho-204 (the cowl guns could be dropped in exchange. But keep the wing cannons).
    The P-39/63 Cobras were likewise not high altitude fighters.
    Their Colt 37mm hub cannons were even much slower at 140 r/m than the NS-37.
    In addition, the Colt M4/M10 was very short range at 460m.
    The NS-37 and the Ho-204 both had stand-off 1100-1200m firing range to fire on the B-29 with impunity from outside the reach of it’s defensive fire, rendering it helpless.
    As you can see, the Ho-37 armed Ki 61 would be unmatched for the task of tackling B-29s successfully.

    3. The Kawasaki engine plant was bombed by B-29s putting an end to the Ki 61.
    What if that were anticipated? The factories should have been more than one and they should have been underground. Such a potentially successful interceptor of B-29s, needed top priority for this. What if it was top priority? Perhaps thousands of
    Ki 61-IIs could have been fielded to stop B-29 raids in their tracks!

    The twin engined interceptors needed to be protected from the US escort fighters, unlike the Ki 61 Tony. It would be potentially equal if it were reliable.
    What other Japanese fighter would be faster (423 mph, US test), and better that high against B-29s and their escort? None!
    With a long range hub motor-cannon? None!
    Capable of firepower that stops B-29s, without return fire? None!

    How’s that for an alternate history of the Tony?


  8. The 30mm Ho-155-II was another option for a hub-cannon for the Ki 61-II. 600 r/m was as good as the MK108. Range was 900m vs 360 for the MK108! The Ho-155-II was much lighter at 44kg as well. With this 30mm cannon in the hub of the Tony, it would still have a good W/L to dogfight escort fighters as well as intercept B-29s with a KO salvo. This gives up the stand-off range of the 37mm Ho-204 to save weight and for fire density in fighter combat of the 30mm. It would be the versatile choice.
    I would not make the 3rd choice of the 20mm Ho-5 as a motor-cannon. In 1945 this was degraded to 600m range. OK in the wings, but in the nose 900m or more range is called for because the US bombers fire back as far as 910m range. The improved W/L over the 30mm is not enough to justify the degraded range of the 20mm for the motor-cannon.
    This is all academic, but the Tony could just as well have had a hub-cannon in WW2. 17,000 Bf 109 Gustavs did with the same basic engine and their 30mm cannon was unreliable as well as short range by comparison to the lighter Ho-155-II.
    The Tony deserved this cannon to face the B-29s. It was the best 30mm cannon in WW2. So, why not? The Tony would’ve been as famous as the Zero now, if this happened.

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  9. The Spitfire Mk V had their wing-cannons freeze at high altitudes without heaters.
    The 20mm Ho-5 cannons in the Ki 61 cowl did not have that problem. This also tightened the turn radius and roll-rate vs the Mauser wing-cannon version.

    In my opinion the Tony should’ve been kept away from the tropics and close to maintenance centers. The Spitfire didn’t have that option against Japan. This unequal advantage could have been better exploited by Japan.
    The radial powered Japanese fighters would pick up the slack in the tropics with less trouble.
    The reliable Ki 44 comes to mind. The Tojo’s short range and meager numbers could be remedied more easily by comparison.

    The IJA took losses in the tropics as punishing perhaps, as the Midway defeat was for the IJN. This was particularly true in the Ki 61 units. Inline engine mechanics were even harder to come by afterward. Like Midway, the skilled support personnel as well as pilot losses had future repercussions. This was doubly true of specialized Kawasaki mechanics compared to Mitsubishi.


  10. It is notable that Japan showed no interest in a motor-cannon.
    The Ki 61 Tony and the D4Y2-S Juby night fighter were powered by the same basic engine as the Bf 109. Thus, they easily could’ve had a 20mm hub-cannon. The IJN Judy night fighter had the potent 20mm Type 99-II at an angle behind the pilot, but a hub position would be easier to aim.
    The Tony had the Ho-5 20mm. Before that, the Ho-3 was too slow and the MG 151 was too few. After the Ho-5 got down-loaded, the 30 or 37mm cannons could preserve the firing range and step up the power in the hub.

    Or the 20mm quartet in the last 30 inline Tony’s could’ve had a quintet like the Italian G.55-II Centauro!
    If the Italians could do it, why not the Japanese?
    It was reliable too.
    Only the Japanese faced the B-29 in WW2, not Italy.
    So, it was certainly called for with the Tony.


  11. As soon as the 20mm Ho-5 was available, it should’ve been in the Ki 61 hub first. Period!

    Where to put another pair is debatable. So, have some in the wings some in the cowl and some with both. Then, combat would prove the best array. The lightweight would be in the wings and hub for best climb, W/L, and dense rounds/sec pattern of fire at the convergence range.
    The hub and cowl would add interrupted gear and cut r/s substantially, but improve roll-rate and turn as well as long-range firepower.
    The heavyweight would be a better bomber killer with all 5 cannons, but suffer as a dog fighter unless combat flaps are added, and perhaps benefit from a rocket boosted climb required for interception. Then the Tony would not be the worst Japanese climber, but perhaps the best as befits a premier interceptor.
    Using all Ho-5 cannons would give harmonized ballistics as a bonus. The auto combat flaps could remedy the problem cannon packing Tony’s had with Spits, F6Fs and P-51s in turn as well as climb rate.
    I would favor the boosters and flaps on all fighters, but I’m not Japanese. But remember Kawasaki was the least Japanese co.
    The booster rocket pack leapfrog the Japanese failure in turbocharging their fighters for lack of rare metals.

    The most likely compromise would be the standard 4×12.7mm version with a 20mm hub cannon simply added. Either the Ho-5 or MG 151/20. The older Tonys could be thus retrofitted.

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