The Kawasaki Ki-61 Hien (Swallow), was the only in-line engined Japanese fighter of the war. The engine was a license built Daimler Benz DB-601, and the plane itself was quite good for it’s day. It was different to most Japanese types in that it combined strength, performance and good armament in a package at the expense of maneuverability and range. In this respect it was closer in concept and performance to European types (Me-109, Spitfire etc) than the traditional highly maneuverable but lightly built Japanese types (A6M, Ki-43 etc).

The Ki-61 performed well throughout the war, but was getting old and less competitive against later war types such as the F4U and P-51D. Some were still being used in defence of Japan against the B-29s late in the war, but it required a very good (and lucky) pilot to make an impact.

Both the German Me-109F and Italian Mc.202 had versions of the same power plant and were built at around the same time as the Ki-61. It is no surprise therefore that these three types are extremely close in style/concept, performance and looks.

Ki-61 pilot Yoshio Matsumoto who fought in PNG and Philippines said that the Ki61 was superior to the P-40, F4F, and F4U, but was out fought by F6Fs and P-38s. Major Yohei Hinoki said that the Ki100 handled so well that he felt confident that he would be able to evade any Allied fighter. On the other hand, he states in his autobiography that when he saw the mock dogfight between a captured P-51 and a Ki-61, he could see that the Ki61 was clearly at a disadvantage.

Maj. Yasuhiko Kuroe, who was piloting the P-51C, said that he felt like he could win over any number of Japanese fighters as long as he was on the P-51.

One trick the Ki-61 was said to have was, when bounced from behind, to whip over into a split-S and pull back around and up for a low head on shot at the attackers underbelly. Edwards Park, in his semi-autobiographical “exaggeration” of his time flying P-39s, “Nanette,” has a fellow pilot say, “Those Tonies are bastards. Little and sharp-nosed and fast. They’re scary.”

Tony: Excellent design, good combination of speed and maneuverability but in the end only a Bf.109E or Macchi 202 equivalent. Should see off a P-40 easily enough and streets ahead of a P-39, but outclassed by a Mustang.

We have to wait until the production of the Kawasaki type 3 fighter (Ki 61 Hien) to see the reversal of the preceding situation of naval technical superiority. And then things were slow and didn’t went exactly as hoped for. Due to a lot of reasons already discussed on the board, the Japanese engine industry was not able to produce a high performance in line liquid cooled engine during the conflict. Things were also complicated by the theater the early Ki 61 were deployed because average heat was considerably higher than in the Homeland. So the cooling system, considered relatively satisfying in the moderate climate of Japan proved to be rather insufficient in New Guinea. Things were compounded there by the lack of mechanics qualification on inline water cooled engine, the lack of sufficient early warning system which complied the fighters under alert status to run their engines for long periods waiting for the enemy which (of course) came when the engine temp required immediate shut down for cooling and recurrent leaks of the coolant (which would have necessitated more qualified mechanics and many unavailable joints to be cured). Add to this the ever present dust in the dry periods which obliged to use natural sponges in the carburetor air intake to filter (thus limiting the plane performances even more than designed tropical filters which never became available) and finally the blockade that dried the parts source and you’ll get the picture why the first apparition of the Ki 61 fighter was not as successful as anticipated (most were destroyed on the ground, not in aerial combat). Though it was probably the most feared aerial foe by the allied in its time! … There were also some other “teething troubles” which were corrected but slowly. Ki 61 Ko was lightly armed by 1943 standard with two wing mounted 7.7 machine guns and only two 12.7 mm heavy synchronized machine guns in the fuselage. It had also a troublesome retractable tail wheel mechanism. Things were fixed a bit with the Otsu where the 7.7 mm wing machine guns were replaced by 12.7 mm heavy M.G’s and the retractable tail wheel fixed with an adequate fairing in its down position. And almost cured with the arrival of German made MG 151 20 mm cannons not only on the production lines but as conversion kits in New Guinea to obtain the Hei… But those importations through submarines were soon to dry.

The Ki 61 was only perfected in 1944 with the arrival of the Tei version which was totally redesigned for ease of production and maintenance, an elongated forward fuselage to incorporate the now Japanese made 20 mm cannons as the wings reverted to the Otsu arrangement with 2x 12.7 mm machine guns. As it was mostly used in much more temperate zones, it was not as plagued with cooling problems as its predecessors and redesign apparently helped maintenance (probably the fact its main area of combat was home defense eased the things too). But the Ki 61 tribulations were not finished… When the even better Ki 61-II was to enter production, both because of the allied blockade and an earthquake the new engine production never met the expected output… So was born the radial engine Ki 100 Type 5 fighter…

KI-61-II KAI

According to my data, the 56th Hiko Sentai operated the Ki-61-II only between May and August 1945. During that period it was based at Itami AB in Hyogo Prefecture, 8.5 miles NW of Osaka. The Sentai commander was Major Haruyoshi FURUKAWA and the Hikotai commander was Capt. Noboru NAGASUE. On 1 July 1945 it came under 11th Air Division/6th Air Army and reported a total of 22 Ki-61-IIs serviceable. It belonged to the air defense forces covering Central Honshu.

Kawasaki Ki-61-II Kai “Fastback” Tony, say that the natural metal finish aircraft bearing either a large red “17″ or a large black “10″ on the vertical fin were from the Imperial Japanese Army Air Evaluation Department at Fussa Air Base, Mainland Japan. The natural metal finish aircraft with a stylized red ‘eagle’ marking on the tail is a presumptuous marking of the IJA 56th Air Regiment. Since production was limited to just 99 examples as a result of engine difficulties, the Ki-61-II as used by the 56th was deployed in defense of the Osaka, Kobe and Nagoya areas only.

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Ki-61 Tei….Long or Short Nosed

The Tei variant, is a “long nosed” variant in the Ki 61-I series. Though it has the same engine than preceding variants. This was due to an in depth re-arrangement of the armament (and partly to the effort to simplify greatly the components of the plane for faster assembly and easier maintenance).

Now the key to operational variants of Ki 61-I (don’t miss the “I” Roman number):

“Short nosed” variants:

Ki 61-I Ko (a) was the original plane with fully retractable tail wheel and two 7.7 mm light machine gun armament in the wings and two synchronized 12.7 mm in the fuselage forward decking.

Next came the Ki 61-I Otsu variant. As it was found the armament was too light against allied planes and the tail wheel retraction mechanism was unreliable, the plane was modified accordingly. Two 12.7 mm heavy machine guns replaced the wing 7.7 mm ones with associated modifications of the bulges on the wings and the tail wheel well was faired over and blocked in “down” position (but the mechanism was still there).

The Ki 61-I Hei was an even heavier armed variant. Its story began when a number of German made Mauser MG 151/20, 20 mm cannons where imported in Japan by submarines. Apparently it was built in conjunction with the Otsu variant on Kawasaki lines but some “conversion kits” were directly sent to New Guinea. In this variant, the wing machine guns were replaced by Mauser cannons with associated modifications.

The next variant was an in depth revision of the plane aimed to simplify assembly and maintenance and use only Japanese parts including armament. The forward fuselage was elongated just after the exhaust line and forward of the windscreen to make place for the installation of Japanese Ho5 20 mm cannon in fuselage decking (the Mauser source has dried out). In the wings the 12.7 mm machine guns returned in a similar arrangement as found on the Otsu. This was the Ki 51-I Tei (d) variant…

Most of the Ko, Otsu and Hei planes found their place fighting over New Guinea though some were retained in Japan.

These ones (mainly and by far Otsu and Hei) eventually found their way to the special attack Chutais of Home defense. Often devoid of armament as they were destined to ram the B 29′s and needed the maximum altitude and speed capabilities to reach their target (notice this tactic was not properly suicidal, the trick was to “land” on the B 29 then to parachute yourself… Some pilots did that more than once and survived! …).

On the contrary very few Tei were sent to New Guinea and most of them were used as home defense fighters in the classical way (though some finally ended in special attack Chutais or units).

The Tei should not be confused with later Ki 61-II which had even longer nose but a completely revised airframe and a new, more powerful engine.