Notes from WATANABE Yoji: Toryu: Jubaku kira (Toryu: Bomber Killer) (Tokyo, Sankei Shuppan, 1983):

After war started, army needed plane that could be used right away, in time for Java attack. Ki-44 & Ki-45 available and hurried into production. (47)

Had 40 days to prepare for test of Ki-45. 6 test planes made and a chutai trained; asked to complete 12 planes. Dec 20, took Ki-45 to Akeno and combat test began. Found that even from a slight angle, 12.7 mm and 20 mm shells penetrated target. But ratio of fire extremely slow: this cannon (Oerlikon) pumps out 127 rounds per minute compared to 525 for Zero gun. So even skilled pilot had trouble hitting target. However, concluded that enemy aircraft would provide larger target, so would have a better chance. (48)

In January tested rear gun and began hit-and-run tests, two-plane hintais. Formation called Rotte after German usage, imported along with test models of Bf 109. (48-49)

Late Jan tested against Hayabusa and Nate. Very difficult to overcome in dogfight, but when Ki-45 had altitude advantage, it could indeed use hit-and-run tactic. Would be possible to fight this way. 12 planes available by now; continued with night flights and groups attacks early Feb. (49)

1,690 Ki-45s manufactured altogether, 80% at Akashi factory. "Reformed" Ki-45 kai ko had speed of 540 kph @ 6000 m. (340 mph @ 20,000 ft); range of 2000 km (1,250 miles). Met 1938 specifications but slow by standards of 1942. Nevertheless, army accepted on 17 Feb. Had already chosen test group: 84th Ind Chutai, which also had Nates, at Gai Lam airport Hanoi. Together with 82nd chutai -- light bomber & recon -- comprised 21st Independent air unit under 25th Army. (51)

Chosen because 1) small group: easy to train pilots; 2) not in heavy combat: able to phase it in; 3) Hanoi has good communications with Japan. Plans completed end of December. Pilots went to Japan and trained Jan-Feb. When 9 planes ready, returned to Hanoi end of Feb. Meanwhile, 4 Nates had shot down French MS 406. (52)

Pilots didn't like Ki-45, and one pilot actually refused to fly it. Hard to start and difficult to fly. Engine and cooling system troublesome. The Nates, by contrast, with decent care was always reliable and ready to fly. Ki-45 therefore required and got continued improvements. (53)

***

Meanwhile, at end of March 5th Sentai in Japan got 6 Ki-45s, which actually scrambled during Doolittle attack but according to new tactical doctrine climbed to high altitude, missing the raiders which came over on the deck. Ki-45s came under fire by friendly ack-ack; had to join up with Nates to land. Army shocked by this raid. Deployed more Ki-45s because Nate too slow. (56-57)

Many accidents in Japan with Ki-45. (60-61)

84th chutai moved from Hanoi to Canton to take part in Se-go offensive against Chinese airfields. Based at Tenko airport, Canton (means something like river/heaven). 19 May, with 54th Sentai Nates, escorted 90th Sentai Ki-48 Lilys to Guilin and Lishui airports; no contact. 20 May to Guilin & Leilo; no contact. 11 June had a report that 9 P-40s arrived at Guilin. So 12 June took off: 5 Ki-45s from 84th chutai, 8 Nates from 54th Sentai, and 5 Lilys from 90th to attack Guilin. (64)

10 P-40s in 2 groups waiting for them. Came in from southeast and bombed airport from 5,000 m (16,500 ft), then changed course. 5 P-40s came down from above and attacked bombers. Nates were to stay with bombers, Ki-45s to drive off attackers, so scrapped with them. Then 5 more P-40s arrived and were engaged by Nates. 54th Sentai reported that P-40 performance good, American pilots cooperated with each other, and used hit-and-run tactics. Battle over in two minutes. Nates claimed three enemy a/c, Lilys claimed one, and Ki-45s claimed three -- total of seven -- plus four uncertain. But lost one Nate, one Lily, and two Ki-45s piloted by 2nd Lieutenant Ieiri (gunner Sergeant Honda) and Master Sergeant Yamada. Another Ki-45 crashed on way back to Canon. So total five. (65)

Realized that Ki-45 at a disadvantage against single-seat American fighters, especially considering that the lost pilots were more skilled than average. Three returned aircraft had expended a total of 70 20 mm shells, 165 12.7 mm bullets, and 293 7.92 mm bullets, from which (considering slow rate of fire) concluded that they did indeed engage the enemy head-on but mostly protected themselves (i.e., by fleeing?). There were wrinkles on the skin of these aircraft. 84th chutai concluded that the plane's performance in battle was disappointing, that it burned too easily when hit, and that its structural integrity was suspect. (66)

Did not follow up this battle. Returned to Hanoi at end of June and made this report to Japan: 1) Ki-45 somewhat faster than P-40 but inferior performance; 2) Rotte tactic needs greater numbers of aircraft; if such numbers are available, then Ki'45's performance must be improved; however, if not, then what is needed is increased speed. They also demand 1) vision to rear should be improved; 2) a supercharger be added to improve engine power for combat maneuvers; 3) belt-type feed be incorporated in 20 mm cannon because couldn't change bullets in air (magazines?); 4) install better system for disposing of empty 12.7 mm bullets (used an ejection lever; in combat didn't have time for that); 5) flexible gun needs improvement of location of bullets; 6) pilot's seat and antenna need attention. (66-67)

Emmanuel Gustin's comments:

But ratio of fire extremely slow: this cannon (Oelikon) pumps out 127: 127 rpm is slower than any WWII 20mm cannon; even the Oerlikon S managed 280rpm. The closest gun in performance would be the 37mm Ho-203 (130rpm), which was indeed installed in some Ki.45s, but AFAIK not in early models. Some early models had a hand-loaded Type 98 37mm gun... I think that Watanabe's memory fails here.

"Reformed" Ki-45 kai ko had speed of 540 kph @ 6000 m.: Note that the Ki.45-KAI-ko was actually the first production model. The original Ki.45 was not accepted by the Army, and the Ki.45-KAI was a complete redesign.

Three returned aircraft had expended a total of 70 20 mm shells, 165 12.7 mm bullets, and 293 7.92 mm bullets, from which: Assume that the 12.7mm gun was the Ho-103 (900rpm), two being carried by every Ki.45; and the 20mm gun the Ho-5 (850rpm) or the older Type 97 (400rpm). Then the 12.7mm guns were fired for a total time of 1.8 seconds, and the 20mm guns for 3.5 or for 1.6 seconds... So more likely it was the Ho-5.

And from Hiroyuki "Harry" Takeuchi in Japan:

I am a 34 year old aviation buff in Japan. I came across your site today and found it very interesting. I think I can contribute a bit of information regarding your Ki45 article.

I have a copy of Yoji Watanabe's book (revised paperback published from Asahi Sonorama in 1989). Watanabe is an aviation historian and what is written is not his personal account, but a result of interviews from many war veterans.

The 20mm cannon described to have only 127rpm is the Ho-3. This cannon was based on the Hotchkis anti-aricraft cannon. However, the Ho3 is described to have a firng rate of 400 rpm in the "Ki number catalog" pubication published by Bunrindo (the Koku Fan people) in 1997. The armarment variation and subtype designations of the Ki45-Kai is as follows (this table appears on Watanabe's revised edition to correct his 1983 book. This is the most recent and now most widely accepted data in Japan);

Ki45-Kai-Ko
12.7mm (Ho103) X2 nose guns
20mm (Ho3) under fuselage
7.92mm  X 1(Type98) for rear gunner

Ki45-Kai-Otsu
12.7mm (Ho103) X2 in nose
37mm (Type 94 single shot tank cannon) under fuselage
7.92mm  X 1(Type98) for rear gunner

Ki45-Kai-Hei
37mm (Ho203)X1 in nose
20mm (Ho3) X1 under fuselage
7.92mm  X 1(Type98) for rear gunner

Ki45-Kai-Tei
37mm (Ho203)X1 in nose
20mm (Ho5) X2 upward firing

Ki45-Kai-Bo
40mm (Ho301) X1 under fuselage

Ki45-Kai-Ko Tei equipment
12.7mm (Ho103) X2 nose guns
20mm (Ho3) under fuselage
12.7mm (Ho103) X2 upwardfiring
7.92mm  X 1(Type98) for rear gunner

Ki45-Kai-Hei Tei equipment
37mm (Ho203)X1 in nose
20mm (Ho3) X1 under fuselage
20mm (Ho5) X2 upward firing

The Specification for Ho3 is as follows
Caliber                   20mm
Length                   1700mm
Weight                   45.0kg
Initial velocity      846 m/sec
Firing rate             400rpm
Shell weight          129.6g