Kawasaki Ki-100

This late War Japanese Army fighter was almost certainly the most important Japanese aircraft to never get an Allied code name.

Let’s take a look at a seriously good airplane that seems to have escaped the notice of Allied intelligence.

I’m sure most readers here will recognize that Japan’s situation at the end of the War was cataclysmically bad. So whatever praise I have for this aircraft, keep it in THAT context.
But the Japanese Army did consider this their very best fighter at the end of the War. It could maneuver with a P-51 Mustang in most aspects, it had heavy firepower, pilot armor and self sealing fuel tanks.

Armament is 4 x 20 mm cannon.
One kill mark, a surprisingly detailed Mustang!

How the Ki-100 came about is an interesting tale. In mid-1944 Japanese Army hierarchy considered the Ki-61 Tony to be their most capable type. But it was clear allied aircraft were getting better so efforts were made to get some improved types in production. The improved type the Allies would become most familiar with was Nakajima’s Ki-84 Frank. But Kawasaki also took up the challenge with an improved Ki-61. That airplane had used a Kawasaki Ha-40 engine. This was development of the Daimler Benz Db 601. It had its problems, but showed great potential. So the engine was improved; a new
Ha-140 in some ways parallels the Db 605, but it was a wholly Kawasaki project. It delivered improved performance, although its reliability remained suspect. Nonetheless, the new Ki-61-II was ordered into production as a next-gen fighter. By the end of 1944 it became a scramble to get the new type into service as the Japanese were starting to combat the B-29.
They lost that race, in the case of the Ki-61-II this was literally true. In January 1945 Kawasaki had completed 275 Ki-61-II airframes, in addition to a small number of complete aircraft. On January 19, B-29s destroyed the engine plant, including all inventory and production capacity of the Ha-140 engine. It was one of the most successful high altitude attacks ever by the Superfortress.
Fortunately for Kawasaki, they had already been looking into a re-engine for their new fighter. In particular, Mitsubishi’s Ha-112 Radial engine. It offered similar power with less weight and much improved reliability. As a radial it had more drag, radials are air cooled which means they do away with the radiator by sticking the cylinders into the airflow for cooling. It was sort of a core argument among aircraft designers on the merits of radial vs in-line (air cooled vs liquid cooled) and involved a long list of trade offs and engineering decisions based on which engine type was chosen for a particular aircraft. So the idea of switching mid-stride, even converting 275 completed airframes, from liquid cooled to air cooled was not arrived at lightly. The conversion from concept to first flight was done in a remarkable 7 weeks.
Even more remarkable is how completely acceptable the re-design was. It became known as the Ki-100 when the new engine was hung on it. New skin was fitted to the forward fuselage to fair the wider engine bearers onto the previously slim fuselage. A single stage mechanical supercharger was fitted that allowed good performance up to 20000 feet. 271 Ki-100-I were converted from the inventory. Test pilots were immediately enthused and felt that with equal levels of pilot experience the Ki-100 could outfight a Ki-84 or N1K in any circumstance. Even better, the type exhibited easy handling and would be a good choice for less experienced pilots.

Far more than 271 new fighters were needed, so new production of the type continued. The next 118 had the rear fuselage cut down for improved visibility. These were tagged Ki-100-I Otsu (or “b”).
A turbocharger was in development for a Ki-100-II but that became a lower priority when the B-29s switched to lower altitude attacks.
Ultimately the Ki-100-Ib was the real end of the line, and the Japanese ability to produce anything came to an end.

Those Ki-100 produced entered service from February 1945. At that late date there was really no turning the tide. But the type was as successful as its numbers allowed. Late War Japanese fighter squadrons typically claimed kills out of all touch with reality (likely a reflection of pilot inexperience), Ki-100 squadrons were no different, but post-War assessments look like they actually did manage about a one-to-one kill ratio. The combination of pilots with a capable mount and Allied pilots who’d grown accustomed to weak opposition did allow opportunities.

A line up of Ki-100 at the end of the War.

Finally, I can’t say with certainty Allied intelligence had NO knowledge of the type, none of my usual sources have a definitive statement on the matter. It seems likely, given how completely Japanese military codes had been compromised, that Air Technical Units had some inkling that a “Ki-100” was out there. It may have been regarded as an improved Tony, maybe even an alternate designation for the Ki-61-II. But it is 100% certain they had not examined one before the end of the War; all but one Sentai of them were based in Japan proper, and that one exception was in Formosa. And pilots did not report the type. It seems it was most often identified as a “Frank”, at least when identification was even in the ballpark (type identification was notoriously bad among all combat pilots, almost certainly the majority were recorded as “Zeros”).

Ki-100 with a Tony. The family resemblance is apparent, but so are the extensive changes to the forward fuselage to fit the new engine.

This particular aircraft was attached to the 59th Sentai, a squadron that completely converted to the type. It was assigned to 1st Lt Naoyuki Ogata, the 3rd section leader was an ace with 5 kills including three B-29s. This plane was photographed post-War with the pronounced victory symbol for a Mustang kill.

Ki-100 with a Ki-84 Frank. The Japanese Army did have two excellent types in service at the end of the War, but not enough and especially, not enough well trained pilots.

This is the Hasegawa kit. It was a simple and fun build.

About atcDave

I'm 5o-something years old and live in Ypsilanti, Michigan. I'm happily married to Jodie. I was an air traffic controller for 33 years and recently retired; grew up in the Chicago area, and am still a fanatic for pizza and the Chicago Bears. My main interest is military history, and my related hobbies include scale model building and strategy games.
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13 Responses to Kawasaki Ki-100

  1. jfwknifton says:

    It must be quite a challenge to shoot down a B-29 from a single engined fighter! Thanks for this blog post. I had never heard of the Ki-100. The closest I got was the Frank at RAF Hendon.

    • atcDave says:

      It is definitely a less known type! Funny thing though, there is exactly one surviving Ki-100 in the world, and it is at RAF Hendon. Apparently it was mislabeled as a Ki-43 Oscar for many years.
      I agree the trick with downing a B-29 in single engine fighter couldn’t be easy. I imagine that’s why they so often rammed. But the Ki-100 did have heavy firepower exactly for that reason.

    • Ernie Davis says:

      One other aspect of the B29 that is often overlooked is that it pioneered the centrally controlled fire system similar to fire control systems that had been used by ships and Anti-Aircraft emplacements for years. The pressurized crew cabin meant that gun turrets needed to be controlled remotely, and the development of a fire control system to do so resulted in defensive fire that was far more effective than exposed gunners at longer ranges than most fighter aircraft could accurately fire their weapons meaning the B29 could engage enemy fighters with reasonably accurate fire well beyond the fighters effective range.

  2. Ernie Davis says:

    I admit that I’m far less informed on the pacific war, especially when it comes to air power. My impression has always been that after the IJN was basically crushed the Japanese never really developed anything that could challenge American air superiority in any numbers sufficient to do so. From what you say the later assumption may still hold, but the former not so much.

    Interesting article to go with an interesting build. I guess there was a lot more to the air war in the pacific than I’ve been aware of.

    • atcDave says:

      Yeah I think the numbers are where the Japanese were crushed. Most of their late war designs did have a litany of problems, but for the Ki-100 it almost entirely about numbers. Although it’s fair to say pilot training was also completely inadequate. By the end of the Solomons and New Guinea campaigns they could never again compete with Allied numbers.

    • Ernie Davis says:

      I guess I always had the impression that the Japanese kind of stagnated with the late model Zero’s and never pushed for new designs once they’d lost any chance of air superiority. Apparently that wasn’t the case.

      • atcDave says:

        I think the problem was more industrial and practical as opposed to conceptual. That is, they were able to come up with good modern designs (at least in terms of hardware, never electronics) they just couldn’t build the quality and quantity they needed.

  3. It’s Interesting that the Japanese managed to pull something out of the bag at such a late point in the war. Maybe by this point though, the allies were more concerned about finishing the job rather than bothering to register new models. Who knows!

  4. RB says:

    The radial engine was so light for the power [1,620 hp WEP by one source]. and then the lead ballast was also discarded from the tail. This allowed it to load more cannon ammo, 250 r/g!
    These 20mm Ho-5 were downloaded but at least they were nose-mounted for best effect.

    • atcDave says:

      I also saw where the Ki-100-II would have been the lightest turbo-charged aircraft of the War had it entered production.
      Apparently many pilots had the wing mounted cannon removed too. That may have been problematic for going against B-29s.
      But the bottom line on all of that is a very light aircraft. Yet not stupid light like the Ki-43 had been. More, light in the best sense of the word; which was used to advantage by applying weight like pilot armor to the places it would do the most good.
      It’s a worthy member of that whole last generation of piston engine fighters.

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