Mitsubishi J2M Raiden, part two

Raiden's performance improvement was focused on fitting the type with a turbo-supercharged engine. The first prototype of this variant was powered by the Mitsubishi Kasei 23hei (AKA Kasei 23a) radial engine rated at 1.820 hp, fitted with the company's own supercharger. The prototype used J2M6's fuselage with two cannons fitted aft of the cockpit. The 20 mm cannons fired upwards, in an oblique way, aimed at seventy degrees, just like the German Schräge Musik system. This version was intended to be used against B-29 bombers that operated at altitudes beyond reach of other Japanese fighters.

The second prototype of this version was powered with the same engine but it featured a different supercharger, this time made by Dai-Nijuichi Kaigun Kokuso (21st Aircraft Arsenal of the Navy) at Sasebo, Japan. This prototype was longer than its predecessor and was also equipped with modified engine cooling gills. It received the designation of J2M4kai Model 32kai and was converted by Yokosuka.

Only two prototypes were made of the J2M4 because of problems with the turbo-superchargers, rendering the mass manufacturing process impossible. According to documents captured by American troops, only one prototype was completed, while the other one was a regular J2M3 converted to a supercharger version.

The next version, J2M5 Model 33 was also going to be a high altitude fighter. This version was tested with a new Mitsubishi Kasei 26 engine (fitted in J2M2 airframes) rated at 1.820 hp. It's not possible to tell if the new cockpit frame and the additional flat profile of the upper fuselage in front of the windscreen was first adopted in this variant or in the J2M6, which was developed in parallel. The production variant, of which a total of 34 airplanes were made between May 1944 and August 1945 in Nagoya (though, according to other sources the total number was 43), was powered with the Mitsubishi Kasei 26ko engine fitted with a three-stage centrifugal supercharger. This feature made the J2M5 the fastest Raiden version as it reached a top speed of 615 km/h (382.143 mph) at 6.800 m (22.3097 feet) high. 
One of the J2M5 was shown in surviving photos armed with two 30 mm Type 5 cannons instead of the usual 20 mm ones.

It's also feasible that, due to limited availability of the Kasei 26 engine, some J2M5 airframes were fitted with the Kasei 23ko engine, making it similar-looking to the J2M6.

The last version, the J2M6 Model 31, looked on the outside like a combination of the J2M3 airframe with the J2M5 cockpit. This version was probably tested using the J2M2 airframe with the new cockpit and the flat fuselage top portion in front of the windscreen. Two prototypes were built between June 1944 and February 1945, but one was converted to the J2M4 standard. This variant appeared before the J2M4 and the J2M5, in spite of its numeration, and was developed in parallel, hence the usage of the Mitsubishi MK4C engine.

There were also some projected variants, that were never completed, like the J2M6ko Model 31ko, which was going to use the J2M3ko airframe combined with the J2M3 cockpit. The J2M7 Model 23 was under development and was going to have the J2M3 airframe, but powered by the Kasei 26ko engine. 

There are also mentions to a J2M8 variant which, apparently, was going to have a cut-down rear fuselage and an all-round vision canopy, similar to the of the A6M Zero. 

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_J2M

2. Mushroom Model Magazine - Yellow Series 6110 - Mitsubishi j2M Raiden 'jack'

3. https://www.valka.cz/Micubisi-J2M-Raiden-Jack-t28908

Mitsubishi J2M Raiden, part one

 

The Mitsubishi J2M Raiden was designed by Jiro Horikoshi, the creator of the Mitsubishi A6M Zero to meet the 14-shi official specification calling in 1939. This specification called for a strictly local-defense interceptor, to defend against high-altitude bomber raids. To meet that requirement, the proposed fighter had to rely on speed, climb performance and armament sacrificing maneuverability. The J2M was a sleek, but stubby aircraft with its oversized Mitsubishi Kasei engine buried inside a long cowling and cooled by an intake fan which was connected to the propeller with an extension shaft.

Work on the project began in March 1940 and, back then, it was very innovative by Japanese standards. It featured a low wing with symmetrical airfoil and slotted flaps with a very low cockpit, to minimize drag. The prototype was powered by a single 1.460 hp Mitsubishi Kasei radial engine mounted in a very slim cowling with a small air intake. This, forced the designers to use a fan to achieve proper cooling. 

All those innovations resulted in serious delays in work on the prototype. Furthermore, with Horikoshi concentrating on development of the A6M Zero, Kiro Takahashi, had to take the lead on the development team, remaining in overall control of the project.

It wasn't until March 1942 that the prototype was completed and the first flight, from Kagamigaura airfield, in Chiba, Japan, took place on 20th May. A total of 8 development prototypes were built.

The J2M2 Model 11 was the first production version, which flew for the first time in October 1942. It featured a redesigned cockpit and a Kasei engine with better cooling system and individual exhausts. A total of 131 machines (155 according to other sources) of this variant were manufactured (which were also heavily field-modified to reduce engine vibration) between October 1942 and 1943, including the fourth prototype, which was the pattern for production aircraft. 

The J2M3 Model 21 was another version with improved armament. The fuselage-mounted machine guns were discarded in favor of two additional cannons in the wings, making the airplane to be armed with two 20 mm Type 99 Model 1 and two 20 mm Type 99 Model 2 cannons. In order to fit the additional cannons, the wings had to be strengthened. It also featured improved armor protection. All those changes made a heavier airplane, with the subsequent performance decrease. When the new framed cockpit of the J2M6 was tested, some J2M3 were retroactively fitted with that new cockpit frame.

It also had a sub-variant, called J2M3ko Model 21ko, which replaced the two wing-mounted Type 99 Model 1 cannons with Type 99 Model 2 cannons placed in underwing pods. Twenty-one machines of this sub-variant were built.

In total, counting all sub-variants, 307 J2M3 were manufactured (438 according to other sources) by Mitsubishi at Nagoya and Suzuka and Koza Naval Aviation Workshop from February 1944 to July 1945.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_J2M

2. Mushroom Model Magazine - Yellow Series 6110 - Mitsubishi j2M Raiden 'jack'

3. https://www.valka.cz/Micubisi-J2M-Raiden-Jack-t28908

Mitsubishi J2M Raiden, foreign users

 

The Mitsubishi J2M Raiden (Japanese word for 'Lightning Bolt') was a single-engined land-based fighter aircraft used by the Imperial Japanese Navy Air Service (IJNAS) during the World War II. Although there were not any official foreign users, some captured exemplars were used by:

• United Kingdom: Two Raidens, originally belonging to the 381st Kokutai, were captured at the end of the war. They were evaluated at RAF Tebrau airbase, in Malaysia, with officer from RAF Seletar, in Singapore shortly after the war, in 1946. Their ultimate fate is unknown.
• United States of America: At least one J2M3 was captured by the United States Army Air Force (USAAF) during the latest stages of the war. It was par of the 301st Kokutai and was assigned to the aerial defense of Manila, capital city of the Philippines. It had previously belong to the 381st Kokutai as it was found to have its original codes overpainted, however other reports claim it didn't have any code when it was captured.
  Anyway, it was found in February 1945 at Dewey Boulevard, in Manila, which was used as an ad-hoc air strip. The Raiden was taken to Clark Field, an air base close to Manila, for testing with the TAIU-SWPA (Technical Air Intelligence Unit - South West Pacific) where it was assigned the code S-12, was stripped of any paint and received US markings with pre-war tail stripes. It was only tested twice, for a total of 3 hours and 20 minutes of duration, before an oil pipe failed, causing the engine to seize up. It was later destroyed on the ground when a B-25 Mitchell collided with it when landing.
  Another Raiden, belonging originally to the 302nd Kokutai, was captured after Japan's surrender, at Atsugi airfield. It was sent to the United States for performance tests It was later acquired by Frank Wiggins Trade School, in Los Angeles, to be used as an instructional airframe. By 1952 it was being used as a park attraction at Travel Town in Griffith Park. It was later donated to the Planes of Fame Museum in Chino, California, where it's on static display nowadays.

Sources:

1. https://en.wikipedia.org/wiki/Mitsubishi_J2M

2. https://captured-wings.wikia.org/wiki/Category:Mitsubishi_J2M

3. https://en.wikipedia.org/wiki/Technical_Air_Intelligence_Unit

4. https://captured-wings.wikia.org/wiki/ATAIU-SEA

5. https://planesoffame.org/aircraft/plane-J2M3

6. https://captured-wings.wikia.org/wiki/C/n_3008

For more profile drawings of captured Japanese planes:
http://www.risingdecals.com/DyingSun/DyingSun_A.htm