Historical Background
In December 1937, the Imperial Japanese Army air Force issued a specification to Mitsubishi Heavy Industries for a long-range strategic reconnaissance aircraft to replace the same company's Ki-15 'Babs'. The request specifically stated an endurance of six hours and sufficient speed (600km/h) to evade interception by any fighters then in existence or under development, but the rest of the specification were open-ended. The result was a twin-engined low-wing aircraft. It had a slim fuselage accomodating a crew of two (pilot and observer) in cockpits separated by a large fuel tank. Further fuel tanks inboard and outboard of the engines gave a total fuel tankage of 1,490 l. The engines were housed in a close-fitting cowlings developed by the Aeronautical Research Institute of the Tokyo Imperial University. The first prototype of the aircraft, designated Ki-46, first flew in November 1939. While successful in many respects, tests showed that it was underpowered and it could only reach 540km/h. Still, it was faster than the latest Japanese fighters at the time, the Nakajima Ki-43 Hayabusa and Mitsubishi's own A6M2 Reisen. The Ki-46 was accepted into limited production as Army Type 100 Command Reconaissance Plane Model 1 or Ki-46-I. The Ki-46 gained the Allied reporting name of 'Dinah'.
To solve the problems, Mitsubishi replaced the original Mitsubishi Ha-26 engines with Ha-102 Zuisei, delivering 1,080 hp at take-off. At the same time the weight was reduced whilst fuel capacity was increased. This new variant, the Ki-46-II was first flown in March 1941 and was ordered into full-scale production with deliveries beginning July 1941. While the Ki-46-I and -II were immune from interception by Allied fighters early in the Pacific War, the IJAAF realised that higher performance fighters such as the Supermarine Spitfire and Lockheed P-38 could change the situation. In July 1942, Mitsubishi was instructed to build an even better performing version, the Ki-46-III. The -III was powered by Mitsubishi Ha-112 Kinsei engines of 1,800hp and featured a redesigned nose and canopy, which was smoothly faired from the extreme nose, eliminating the 'step' in earlier versions. The new variant first flew in December 1942.
Also in
1942, following the Doolittle Raid, the Japanese realised the problem of dealing with future American high-altitude bombers hitting the Home Islands. Advanced interceptors for army and navy aviation would not appear before 1944, so interim interceptors would have to be developed from existing aircraft. There weren't many aircraft in the IJAAF inventory that can fit the bill. The IJAAF's version of the heavy fighter was the twin-engined Kawasaki Ki-45 Toryu. The Toryu was capable of carrying powerful weapons, but had insufficient ceiling, and its performance characteristics are not terribly better than its intended victim On the other hand was the Ki-46. At the turn of 1942-43 it was the fastest plane in the Japanese inventory with good altitude performance. The Army decided to turn the recon planes into fighters. The Ki-46-II was selected and the Tachikawa Techical Research Institute installed a Type 98 37mm gun in the nose with the breech under the pilot's legs. The gun was manually loaded and in a relatively cramped
cockpit was a big problem, dividing the pilot's attention. The gun has a rate of fire of
one shot every three minutes. The 644-gram shell was theoretically able to down a B-17-sized target with a single shot.
The first conversion was completed in January 1943 and the tests were satisfactory. Seventeen aircraft (including the prototype) were converted, enough to form a Chutai (squadron). On February 1, 1943 the new interceptors were loaded on board the escort carrier Taiyo and were sent to Truk where they worked out tactics of the new interceptor. As reported by pilots, the heavy gun and reinforced nose portion shifted the CG of the aircraft making it extremely unstable.
As a result, only six of the 17 modified aircraft were transferred, in late
February, to the 10th Sentai staffed by the recon crews of the standard
Ki-46. Despite the apparent failure of the Ki-46 as a fighter, the Army Command still felt the need for such fighters.
In February 1943, when the air battles over Rabaul entered a critical
stage, the reconnaissance Dinah were used as a stop-gap air defence aircraft. Since they were unarmed, save for a single self-defence machine gun, the Dinah used 'Ta-Dan' aerial bombs. The Ta-Dan contained thirty 300g cluster bombs and were released over the enemy bomber formation.
The pilots claimed six B-24 Liberators and two B-25 Mitchells.
The next attempt to create an interceptor based on the 'Dinah' were begun in May 1944 , when a dedicated interceptor based on the Ki-46-III was developed. The nose was reworked again and
two
20-mm cannons were installed with 200 rounds of ammunition per gun. Due to the lack of space in the nose of the aircraft, the left gun was placed slightly forward. All recon
equipment were removed and individual exhaust pipes were replaced by a common collector, to give less glow at night. Also, there was an additional fuel pump, to allow a sharp climb without 'choking' the engine. The fighter version received official designation Ki-46-III KAI Otsu or Army Type 100 Model III Modified Air Defence Fighter. The 1st Army Arsenal in Tachikawa modified 55 regular 'Dinah', with
another 20 directly converted on the assembly line. In July 1944, the IJAAF introduced the
Ki-46-III KAI Otsu-Hei. The fuselage fuel tank was replaced with a 37mm, angled 70 degrees forward and
upward a la the Luftwaffe's Schräge Musik installation. Up to sixty 37mm rounds can be carried. Only 15 Otsu-Heis were built.
In parallel with the field-modified Ki-46 interceptors, the 17th Dokuritsu Hikotai (independent
squadron) equipped with Ki-46-II and -III, stationed in Chofu, modified a
number of their aircraft in the field.
In November 1944, six Ki-46-IIs and one Ki-46-III were fitted with a 37
mm gun in a similar manner as the official Ki-46 KAI Otsu-Hei. All the fighter (and also the reconnaissance) Dinahs can carry the Ta Dan aerial bombs. The Otsu-Hei were only used by by the 16th and 17th Dokoritsu Hikotais. Despite originally having superb performance as a reconnaissance aircraft, the Dinah were weighed down by the 20mm and 37mm (in the Otsu-Hei variant) cannons and their ammo. This in turn affected its climb rate, making it hard to catch the B-29s. The Dinah also lacked armour and self-sealing fuel tanks, making it an easy meat for the bombers' defensive fire (and later, escort fighters). The structural lightness of the designed also caused problems when the 37mm gun is fired. When the B-29s shifted to low-level, night operations, the Dinah became virtually useless as it had no radar. The pilots were also picked from among the recon crews, who were not trained in fighter tactics and lacked combat experience. They tend to rely more on Ta-Dan bombs rather than the cannons when attacking the Superfortress formations. On the other hand, the reconnaissance Dinah were used to report the incoming raids as they had the altitude and speed necessary to track the B-29s.
The Kit
Tamiya styled its kit of the Ki-46-III KAI as 'Hyakushiki Shitei III Kai Air Defence Fighter'. The kit was first released in 1997 and was the second 1/48 kit of the Ki-46 in their catalogue. The kit parts were spread among five light grey and one clear sprues and one decal sheet, printed by ScaleMaster. Most of the parts share the same parts with the recon Dinah kit, with the extreme nose separately moulded. The new 37mm cannon parts looked rather simplified though. While parts for the recon version were omitted, perhaps some more common items such as radio and oxygen bottles can be retained, plus additional items such as ammo racks. Also included were two Ta-Dan aerial bombs. Decals were provided for three aircraft - two of them were Otsu-Hei variant and the other is an Otsu. The Otsu-Heis were from the 16th and 17th Dokoritsu Hikotai while the Otsu was from the 28th Hiko Sentai.
Construction
Construction starts with the wings...just kidding. The cockpit parts were painted Japanese interior green using the mixture recommended by Tamiya with the details painted XF-57 Buff and X-18 Semi-Gloss Black. As for the rear cockpit, I decided to build the Otsu-Hei. As mentioned before, the gun parts were simplified, consisting of just two parts. and, as stated before, the rear cockpit looked empty. It would look even more empty (some modelers said it actually looked unfinished)
if one builds the Otsu version with just the mount for the 37mm gun sticking out of the floor. The fuselage halves were also painted the interior green and once dry, the cockpits were trapped between them and Tamiya Extra Thin Cement were used to seal the fuselage. But wait, did I say I wanted to build the Otsu-Hei version with the slanted 37mm gun? Yep, I forgot to drill the hole for the gun barrel mount!
The next step is concerned with the wings. First, I assembled the landing gears. The kit's engineering splits the wheel well, resulting in a seam down the middle. The seam was hard to remove as the landing gear, which is to be sandwiched between the well halves, were in the way. The completed wheel wells were then inserted into their places in the lower wing. The wheels were however left off at this time. I also decided to fit the Ta-Dan bombs, so the holes for the pylons were drilled. The upper wing halves were then cemented together. After the cement has cured and while preparing for the next step, I realised that I forget to open up the recess for the spotlight! Something else have to be done to make up for this error (more on this later). The wing assembly and the tailplanes were then attached to the fuselage. Like the main wheels, the tail wheel was left off until after painting. The engines were then assembled and attched to the model while all clear parts were also left off save for parts C4 and C7, which was shown to be painted over in the instructions.
I actually built this model several years ago. At the time, I decided to finish the model in the colours of the 17th Dokoritsu Hikotai, just to be different from the other Japanese aircraft in my collection. However after several years, the ID panel and the air defence 'bandage' decals started to crack. I decided to repaint the model, using the leftover decals. The paint were stripped off using window cleaner and isopropyl alcohol. The interior colour was repainted XF71 Japanese Interior Green whilst the lower colour was painted using the same mixture as suggested. It was the upper colour however that I faced some problems, chiefly, I had run out of XF13 JA Green (should have checked beforehand). To get the JA Green shade, I experimented using Tamiya XF11 JN Green into which was added a few drops of XF3 Flat Yellow. The shade somewhat looked like JA Green and having satisfied with the colour, I added XF-69 NATO Black (instead of XF-1 Flat Black as suggested) and some XF-2 Flat White for scale......or so I thought. The resulting colour, while darker than scale-effect JA Green, wasn't dark enough. By this time, I'm no longer interested in repainting the model and left it as it is. Besides, some online reviews mention that the 16th Dokoritsu Hikotai's aircraft were painted the 'normal' JA Green. The ID panel on the wing leading edge were painted using a mixture of XF-3 Flat Yellow and XF-7 Red.
The model was then re-decalled and I have to say that, at least for this kit, the Scalemaster decals behaved almost like cardboard rather than decal. They don't conform to bumps and bulges (the wing Hinomarus, in both builds, were torn when I tried to force them over the aileron mechanism) and they didn't react well even to Mr Mark Softer. The wing Hinomarus were then touched up with XF2 Flat White and X-7 Red. I however couldn't find the numeral '24' and couldn't any suitable substitute (the decals from my Hasegawa A6M5c can be used but I only discovered them in another box, used for spare parts after the model has been completed). Browsing the internet, I found that the only photos and profiles for the Otsu-Hei variant were those for the brown 16th Dokuritsu Hikotai and aircraft numbered '17' and '24' of the 17th. So applying artistic license, I cut off number 16 (it was about the same font type and size) from my Hasegawa N1K2 Shiden decal sheet and applied it to the model.
Finishing
The rest of the parts can now be cemented. These include the propellers, nose cannons, main wheel tyres, pitot tube, the tail wheel and the Ta-Dan bombs. The oblique cannon were glued into place using superglue, after the placement tab was shaved off. The cockpit transparencies fit nicely for the pilot's but the rear cockpit has some fit problem, especially for the sliding part. The model was then subjected to the usual sludge wash and the final spray of flat clear.
Well, it's a Tamiya. Just place a tube or a bottle of cement and a sprue inside the kit box, give it a good shake and out comes a fully assembled model. Apart from some goofs, such as incomplete rear fuselage, the fit of the canopy and the crap decal sheet, the kit came together easily. Highly recommended for aircraft modelers especially those who have great interest in Japanese aircraft of World War 2.
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