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Nakajima Type 1 Model 1 Army Fighter (Ki 43-I) Armament -- A Reassessment (part 2)

continued from part 1


In the autumn of 1942 things were not going well for the Japanese in their Southeast Area - primarily the Solomons and New Guinea. It was decided to send JAAF units to the area to bolster Japanese Navy air units already there. Among these was the 12th Hiko Dan (Flying Brigade, hereafter Brigade or FB) consisting of the 1st and 11th FR equipped with Ki 43-I's. Before leaving these units were brought up to above normal strength in both aircraft and pilots [12].

The 11th FR transferred from Soerabaja to Truk by aircraft carrier in December 1942. Fifty-seven Ki 43-I's were flown from Truk to Rabaul on December 18th. As of December 31st the 11th had sixty-one aircraft in the Southeast Area including three unserviceable aircraft on Truk. The 1st FR followed a month later with fifty-nine Ki 43-I's [13]. These units are of particular interest since they are not only examples of Ki 43's in the Southeast Area but brought with them aircraft formerly with other units in other areas.

In addition to the 120 Ki 43-I's the 1st and 11th FRs brought with them, replacement aircraft accumulated at Truk by mid-March 1943 amounted to an additional seventy Type 1 fighters [14].

These 190 Ki 43-I's represent over 25 percent of total production and with some thirty additional replacements previously forwarded from Truk constitute nearly thirty per cent of total production. Only relatively few of these aircraft were new. The 1st and 11th had initially received the Ki 43 in mid-1942. As already noted they had received hand-me-downs from other units prior to transfer. Of the seventy Ki 43's on Truk in March 1943 only thirteen were new. Others had previously been used by combat units and some had come from the Akeno training center. A number were damaged and had to be repaired on Truk or returned to Japan. All in all the equipment of these units was a good representative sample of Ki 43-I aircraft.

Without detailed records of the armament of each aircraft of the 1st and 11th FR we can still establish by strong circumstantial evidence that the mixed armament was in use. First, the Japanese 6th Air Division logistics plan for supplying ordnance to these units was based on about twice as many 7.7 rounds as 12.7 rounds. This proportion was exactly the same as for the Ki 61 but with one half the quantity. The Ki 61 was then armed with two 7.7mm guns and two 12.7mm guns or double the Ki 43-I's armament. Second, all four Ki 43-I's captured at Munda in mid-1943 were so equipped [15]. Finally, we have a record of the ammunition expenditure of the 1st and 11th FRs during their first months of operations. The 11th expended 28,111 rounds of machine gun ammunition and 18,895 rounds of cannon shells. Figures for the 1st are 4,023 and 3,067 respectively [16]. Actual expenditure of 12.7mm ammunition was about 40 per cent of the total for the two units. This compares to 30 per cent planned and compares closely to the 39 per cent for the 59th FR in early 1942.

To return to the Ki 43-I's captured at Munda. Their armament was described as "one fixed 7.7 mm machine gun, type 89 improvement B, mounted on the top right side of cowling and synchronized. One fixed 12.7 mm machine gun, B, mounted on the top left of the cowling. Ammunition was described as standard ball and tracer for the 7.7mm with approximate capacity 500 rounds. A.P., H.E., and H.E. tracer for 12.7 mm with approximate capacity of 300 rounds. It was noted that it is possible to install two 12.7 mm without change in mounts [17].

These aircraft bore serial numbers 493, 685, 695, and 725. Their production dates range from June to mid-October 1942. These aircraft represent the 393d to 625th production aircraft out a little over 700 produced.

A representative list of 11th FR aircraft is found in the status report for No. 2 Chutai aircraft of that Regiment as of December 31, 1942 [18]. Serial numbers range from No. 283 to 670 with 283 being an anomaly as no other serial numbers in the 200's or 300's are included. Other aircraft serial numbers were 414, 424, 450, 474, 579, 586, 634, 641, 649, 653, 658, 664, and 670. Number 646 had washed out in a force landing on December 29th (N.B. this was one of the Lae wrecks).

Ki 43-I wrecks catalogued by Allied intelligence at Lae after its capture included: Nos. 239, 328, 397, 400, 426, 466, 520, 622, 646, 674, 805, and 810 [19]. Many of these aircraft were completely wrecked and stripped. Available evidence does nothing to suggest other than that these aircraft had the "standard" mixed armament of one 7.7mm and one 12.7 mm. One of the last comments on the Oscar Mark I appearing in a Southwest Pacific intelligence report stated: "The armament of Oscar always consists of two synchronized guns...Normally one 7.7mm Vickers type gun is mounted in the left blast tube and one 12.7mm Browning type is mounted in the right blast tube."[19a]


The twin 12.7mm version of the Ki 43-I did get into field service. The Chinese captured one. This aircraft was captured on May 1, 1942 at Leizhou Bandao. In the Summer of 1942 both the 10th Independent Air Squadron and 24th FR operated the Ki 43 in China and the Flying Tigers had apparently first observed the type in operations over China early in July, however, neither unit was equipped with the Type 1 fighter as early as May 1st and this particular aircraft belonged to the 1st Field Replacement Unit [20]. A crash intelligence report specifically states this aircraft was armed with two guns of approximately 13mm caliber [21]. The aircraft was repaired and tested by the Chinese who assigned it serial number "P-5017."

Given that two pre-production Ki 43-I's were fitted with these weapons it does not seem surprising to confirm that this variant was flown in the combat theater. However in light of several published reports that this variant with two 12.7 mm guns (ostensibly the Ki 43-IC) was the major production type, it seems surprising to find so little evidence of its operational use.

More surprising than the existence of one (possibly more) twin 12.7mm versions in an operational theater is evidence of late production versions equipped with twin 7.7mm guns. The wrecks of three Ki 43-I's (s/ns 776, 804 and 808) were found at Cape Gloucester, New Britain in December 1943 [22]. Two were equipped with two 7.7mm machine guns and the third was in a demolished condition and its armament could not be determined.

It seems highly unlikely that late in its production life the Ki 43-I reverted back to its prototype armament configuration. A more likely explanation is that these aircraft were retrofitted in the field. As noted from earlier comments in this paper the conversion could be done rather simply without structural changes. Such an explanation begs the question, why?

While some Ki43-I's from the 1st and 11th FR may have been repatriated to Japan for use as trainers or as a source of parts, a number were left behind in the Southeast Area. At least one was used by the 14th Field Air Repair Depot for liaison purposes [23]. Others probably went to the 13th FR that partially converted to the Ki 43 in addition to its Ki 45's after suffering heavy losses at Wewak in August 1943. Some of the Ki 43-I's may have been used as trainers. The two twin 7.7mm armed aircraft captured at Cape Gloucester were painted blue. A similarly painted aircraft was later captured at Alexishafen, New Guinea. This unusual paint scheme may suggest that these aircraft were used for other than normal operational purposes. The 13th apparently received its first Ki 43-I's in August and its first Ki 43-II's in September [24].

If, as seems likely from the evidence, Ki 43-I's were used for liaison and training purposes from August 1943, it would not be surprising to find their 12.7mm guns salvaged as spares or for use on other operational aircraft. Speculation? Yes, but more plausible than the production line turning out these lightly armed aircraft when 12.7mm cannon were more available than earlier [25].


One nagging question remains. If the twin 12.7mm version was actually tested during the Ki 43's prototype phase and the 59th and 64th FR's were supplied with some of these aircraft early in the war, why did the vast majority of production models receive a mixed armament rather than two 12.7mm guns?

The explanation is suggested by information provided by Hiroshi Ichimura based on conversations with former 64th FR pilot Yoshita Yasuda. The early versions of the 12.7mm Ho-103 were simply not reliable and were subject to jamming. On occasion a shell would detonate in the barrel damaging the engine. The 64th may have lost as many as three aircraft to this cause during the Malayan campaign. The fix for this problem before more reliable versions of the gun were available was to mount iron plates on the blast tubes. These plates were in fact found on captured aircraft. The mixed armament was a compromise. The power of the relatively unreliable 12.7mm machine cannon was combined with the great reliability of the less powerful type 99 machine gun [26].

The "received" version of the history of Ki 43-I as discussed in the Introduction is almost certainly wrong. If the Ki 43-I was originally placed in production with two 7.7mm machine guns, these early aircraft either did not go into action or were modified with one 12.7mm machine cannon prior to doing so. In early combat operations the 59th and 64th FR almost certainly operated some aircraft with the twin 12.7 gun armament but not to the exclusion of the mixed gun version. The ammunition expenditure data indicates these units progressively increased their 7.7mm ammunition consumption to levels consistent with exclusive use of the mixed gun type. That this progression took place rapidly is enforced by the assertions of Dr. Izawa and 64th veterans that do not even mention the twin 12.7mm version being used. Three Japanese Monographs in addition to the one providing ammunition expenditure data provide general support for the mixed armament being used in early operations.

Crash intelligence regarding aircraft of the 50th and 64th FR indicates this armament was still in use by these units in Burma in October 1942.

The 1st and 11th FR took the Ki 43-I to the Southeast Area in late 1942 and early 1943. The evidence strongly indicates that their aircraft (which represented a significant portion of the Ki 43-I fleet) were fitted with the mixed armament.

Limited examples of other versions of the Ki 43-I were found. However, even if these aircraft were produced with two 7.7mm or two 12.7mm guns and not modified in the field, their serial numbers are out of sequence with the commonly accepted history of this aircraft. The production sequence: A (2x7.7) -B (1x7.7 and 1x12.7) - C (2x12.7) clearly did not occur.

Based on the evidence marshaled in this study (which admittedly does not take into account all units equipped with this aircraft much less present direct evidence as to each aircraft) the main operational version of the Ki 43-I was equipped with one 7.7mm machine gun and one 12.7mm machine cannon. This version was in operation in Indo-China and Malaya early in the War; in Burma in late 1942; and, in the Southeast Area from late 1942 to mid-1943. A captured aircraft in China confirms the version with two 12.7mm machine cannon but reinforces the impression that this configuration was limited to a small number of early production aircraft. While versions with two 7.7mm machine guns existed, they were likely retrofitted aircraft relegated to non-combat roles.

Notes in part 3