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.
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.
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”).
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.
This is the Hasegawa kit. It was a simple and fun build.
Plane Dave 
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.
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.
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.
Yes, in addition to just being big and sturdy. The B-29 was a tough customer in every sense.
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.
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.
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.
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.
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!
The resourcefulness is impressive.
It was indeed!
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.
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.
A great post describing the Ki-100. Most people simple group all the Japanese planes in the name of Zero.
Yes, and that was true during the War too!
And every German tank was a Tiger
So true!
Exactly!
Well I will admit as a limited defense for the Tiger, the main German battle tank of the late war, the Mark IV was often deployed with armored skirts, especially around the turret, that gave it a profile not dissimilar to a Tiger mark VI, and my guess is that accurate identification was not the top priority of the crews at the time, so I suppose any air cooled rotary engine Japanese fighter likewise became a Zero in similarly stressful situations
You can argue that “all” German tanks had a certain Teutonic aesthetic, just as most Japanese aircraft had the same light/slim (for a radial engined aircraft) look.
And yes combatants often had other things on their mind.
But having spent a career at a GA airport, I’ve seen SO MANY fellow controllers who simply call any high wing civil aircraft a “Cessna” (like they’ve never even heard of a Luscombe, Stinson or Piper Cub) I would say a shocking number of professionals pay very little attention to things that are really a part of their profession! So in that sense I’m really not surprised by the lack of attention to detail. But it is often surprising when you read an account by someone you expect to be a very capable professional getting it all wrong, like Werner Molders wading into a squadron of Hurricanes he identifies as Spitfires or Tommy McGuire fighting Oscars over Wewak, New Guinea (five hundred miles from any IJN base) and calling them all Zeros.
I remember when I was doing research for this article one Japanese pilot said what he liked about the plane was 20 mm cannon in the nose, and no wing guns to hamper maneuverability. Errrr, but the Ki-100 DOES HAVE 20 mm cannon in the wings. So, huh. I did find a quip that some pilots had the wing guns removed to improve maneuverability. Okay. But that suggests the pilot in question did not even know his aircraft was non-standard?
It is often surprising to me the things well trained professionals get wrong or don’t know. I suppose its not much different from any comments about the unreliability of eye witnesses. It just tends to jump when those you expect to know better, do not. (hey, I can tell a Cessna 172 from a Cessna 182, why couldn’t most of my co-workers?)
And thus, the job of the historian is born since the first draft, and the first drafters can’t always be taken as definitive fact. The frustration and fun are, well, up to the practitioner to decide.
Yeah funny. The frustration is some of the fun of it. And there are SO MANY details I suppose.
I’m currently reading an account of the Second Naval Battle of Guadalcanal. Probably the 20th or so such account I’ve read. So how is it I never knew before that Thomas Gatch (Captain of the South Dakota) went into that battle just three days after being injured in an air attack. His left arm was riddled with shrapnel and his Aorta was severed. So on the ship’s bridge that night he went into battle with his neck stitched, bandaged and immobilized; and his arm in a cast and immobilized over his head (!). You may know the story, how on its first salvo a circuit breaker popped that took ALL the ship’s weapons off-line for 20 minutes. I can’t even imagine that level of stress on a badly wounded Captain and the impact that could have had on things. I’ve read so much about that battle and somehow never came across that rather interesting tidbit. Or maybe it never registered before?
And that goes back to your comment about paying attention to other things. The are often just so many other things!