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.