Mitsubishi J2M3 Intercepter Raiden (Thunderbolt) Model 21 “Jack”

J2M3_Jack01

“Lt. Sadaaki Akamatsu was the Japanese version of the infamous “Pappy Boyington.” He entered the Pacific war in China, and amassed more than 8,000 flight hours during his carrer. “The time before WW II, fighter planes did not have the great speeds. It was the pilots ability that counted, and it became known as the one-to-one dogfight era. The combat of this era wasn’t fast but slow and determined. One by one, we announced our identities and fought to the end. We didn’t fight in mass formations.”

Akamatsu was widely known as the “Master of the Raiden.” With the Allied code name of “Jack,” this stubby interceptor was designed to attack B-29’s. It carried two 20mm cannon in each wing, and could attain a speed of more than 380mph. It’s only drawback was it’s lack of maneuverability. ”

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Strengths:

Firepower  – Its four 20mm cannons give it firepower equal to all but the 30mm equipped planes.

Weaknesses:

Speed  – A top speed of only 371 mph at altitude leaves the Jack outclassed by contemporary fighters, which were well over 400 mph by the time it saw service.

 

Showing remarkable foresight, the JNAF decided to build a land-based interceptor, with Mitsubishi’s Jiro Horikoshi being consulted about the project as early October 1938. However, the needs of the A6M project kept the interceptor idea on hold until September 1939 when the specifications were first drawn up.

The specification called for strict takeoff performance characteristics, with the plane having to take off in overload condition in under 300m. With an endurance of 45 minutes, it was supposed to be able to attain a speed of 600 kph at 6,000m (373 mph at 19,685 ft) and had to climb to that altitude in less than 5 1/2 minutes. For the first time the Navy included a requirement for protective pilot armor and, remarkably, the specification included no maneuverability requirement at all.

Intended to use the same Mitsubishi Kasei engine as they had used in the Zero, the Raiden was designed for maximum streamlining and drag reduction. The engine was mounted further back from the front of the cowl than normal, allowing the cowl to be tapered to keep drag to a minimum. A long shaft connected the engine to the propeller gear and an engine driven fan was installed in front of the engine to maximize airflow for cooling. The wing had a low aspect ratio and was designed with a laminar flow cross-section, while the cockpit canopy was low and wide with curved glass, all intended for drag reduction.

The low-priority of the project combined with cooling and laminar flow problems so that the first J2M1 prototype wasnít flown until March 20, 1942. Numerous problems plagued development including the inability to raise the landing gear at speeds greater than 100 mph! However, the airframe was stable and had good controllability at all speeds from stall to 325 mph, with the ailerons getting a little heavy over that speed, so the decision was made to go ahead with Service Trials.

As expected, pilots complained about the curved canopy glass that distorted their view during landings and the propeller pitch change mechanism was unreliable. The speed and climb rate fell far short of specifications and so Mitsubishi was ordered to try and improve on these characteristics.

The first change was to replace the Kasei 13 with a more powerful Kasei 23a modified to accept a water-methanol injection system. The complicated and unreliable extension shaft was deleted and the cowl length was reduced to improve over-the-nose visibility. The curved glass problem was fixed by adopting a new canopy and windscreen that utilized optically flat armored glass at a slight cost in increased drag. To further improve speed, the collector exhaust was replaced with individual “ejector” stacks designed to produce a small “jet” effect.

The J2M2 was accepted for service in October 1942, but again A6M priorities coupled with problems to delay production. The engine smoked excessively at maximum power and at certain power settings sympathetic vibrations set in that in some cases shook the plane apart in mid-air. This was fixed by reducing the rigidity of the engine mounts while increasing the rigidity of the propeller blades.

The second J2M2 was destroyed and the pilot killed shortly after take off on June 16, 1943. Mitsubishi engineers were unable to determine the cause of the crash until the tenth J2M2 had a similar mid-air incident. Fortunately the pilot immediately put the landing gear down and was able to make a safe landing. It was found that the tail-wheel shock strut was pressing against the elevator controls when retracted, causing the plane to nose over and the problem was rectified immediately.

By March 1944 only a little over 150 Raidens had been produced, the whole program being delayed by teething problems and the priorities of other projects. Along with the introduction of the J2M2 to squadron service, the first J2M3 was produced. While it retained the same engine as the previous model, it had a stronger wing. The new wing allowed the armament to be improved by removing the 7.7mm machine guns in the cowl and augmenting the two 20mm Type-I cannon in the wings with a pair of improved, faster-firing 20mm Type II cannon.

However, performance still fell well below specifications and the Navy decided to phase out the Raiden and to concentrate their efforts on the Kawanishi Shiden to fill the interceptor role. A small number of Raidens served in the Philippines campaign where they earned the code-name “Jack”, but most were used in the home defense role where their heavy armament and pilot protection made them better suited to the bomber interception than to duty under tactical conditions.

 

Sources:
Francillon, Rene J.; Japanese Aircraft of the Pacific War; Naval Institute Press, Annapolis, MD; 1979.
Green, William; War Planes of the Second World War Fighters Volume Three; MacDonald & Co, Ltd., London; 1961
 

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