Mitsubishi J2M3 Model 21 in US colours from the left
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Introduction and Development
Service Record
Variants
Specifications J2M3
The Mitsubishi J2M Raiden (Thunderbolt) 'Jack' was a land-based interceptor that emphasised performance and pilot protection rather than manoeuvrability, and that would have been of great value to the Japanese Navy if its combat debut hadn’t been delayed until 1944.
Work on the J2M actually began in October 1938, when Mitsubishi and the Japanese Navy began to discuss the idea of producing a land-based interceptor to work alongside the more manoeuvrable carrier-borne fighters. At this time Mitsubishi were developing the A6M Zero, and so work on the new concept was slow. Its official 14-Shi specification didn't appear until September 1939, and the first prototype wasn't ready until 1942.
The specification called for a cannon armed single-seat interceptor, with a top speed of 373mph at 19,685ft, that would take no more than 5 minutes 30 seconds to reach 6,000m, with an endurance of only 45 minutes, and that would have armour plating behind the pilot's seat. This contrasted with the Zero, where manoeuvrability and range were seen as more important than protection.
Jiro Horikoshi, head of the design team that worked on the J2M, was restricted in his choice of engines. Eventually he decided to use the 1,430hp Mitsubishi Kasei, a fourteen-cylinder radial, even though most of the best fighters of 1939-40 used inline engines. This engine had a large frontal area, and in an attempt to reduce drag it was connected to the propeller via an extension shaft. An air driven fan directed cooling air onto the engine, and the entire setup was contained within a tapered cowling. The engine was thus much further back within the fuselage than on most radial engined aircraft, and the nose was much more streamlined.
Work on the J2M progressed slowly, with most effort going on the A6M Zero. The prototype wasn't completed until February 1942, and it didn't make its maiden flight until 20 March 1942. At this stage the aircraft was disappointing. Its performance wasn't as good as expected, the sloped windscreen reduced visibility, the landing gear was problematic and the Kasei 13 engine and extension shaft unreliable.
Most of the problems were solved on the J2M2. The Kasei 13 engine was replaced with a Kasei 23a, which had the fan cooling system built in. This allowed the cowling to be reduced in length, improving visibility. This was the first Japanese engine to use water-methanol injection, which provided a performance boost, but caused some delays. The unpopular windscreen was also removed, and was replaced with an optically flat bulletproof screen.
Production of the J2M was as slow as its development had been. Only fourteen had been completed by March 1943. It wasn't issued to an operational unit until the late summer of 1943, and only 141 aircraft were produced between March 1943 and March 1944. In June 1944 the Navy decided to adopt the Kawanishi Shinden as its main land-based interceptor, but to keep the J2M in production until the Mitsubishi A7M Reppu was ready to enter service (this aircraft, designed to replace the A6M Zero, had barely entered production at the end of the war).
Eventually six units were equipped with the J2M. A small number reached the Philippines, where they made an unsuccessful combat debut during 1944. The J2M was more successful as a bomber destroyer over Japan, where its climb rate, pilot protection and 20mm armament came into its own. A number of aircraft were given the obliquely mounted 20mm cannon tested on the J2M4, similar to the 'jazz music' installation used by the Germans.
The different variants of the J2M demonstrate the complexities of the Japanese Navy's designation system. The familiar letter/ number codes move up in sequence from the J2M1 prototype to the proposed J2M7, but the model numbers appear to move in the opposite direction (after the Model 11 J2M2 and Model 21 J2M3), from the Model 23 J2M7 to the Model 34 J2M4. In the model number the first number is the airframe version, the second number the engine, so the J2M2 was the first airframe, first engine, the J2M3 the second airframe, first engine. The J2M4 is something of an anomaly, with the third version of the airframe but the fourth different engine, suggesting that plans were already in place for the third engine, which appeared on the J2M5. Presumably a second engine type was given a code, but not used on any aircraft that received a J2M designation.
J2M1
The designation J2M1 was given to the prototype version, with the unsatisfactory Kasei 13 engine. Three were built before the improved J2M2 appeared. The J2M1 was armed with two .303in machine guns in the fuselage and two 20mm Type 99 Model 2 cannon in the wings.
J2M2 Model 11
The J2M2 Model 11 was the first production version of the aircraft. Mitsubishi built 155 J2M2s, and they were the only production versions to carry two 7.7mm machine guns and two 20mm cannon. The J2M2 used the Kasei 23a fourteen-cylinder radial engine, in place of the Kasei 13. The windscreen was also modified.
J2M3 Model 21
The H2M3 Model 21 was the first version to be entirely armed with 20mm cannon. The fuselage mounted machine guns were deleted, and the wing modified to carry four cannon - two Type 99 Model 2 cannon with protruding muzzles and two Type 99 Model 1 cannon contained entirely within the wings. At first the J2M3 was produced alongside the J2M2, but it soon replaced it on the production line. Mitsubishi produced 260 J2M3s, just over half of their entire production run of 476 aircraft.
J2M3a Model 21a
The J2M3a was similar to the J2M3, but with the slower firing Model 1 cannon replaced with two Model 2 cannon carried in pods under the wings. Only 21 were built.
J2M4 Model 34
The J2M4 Model 34 was given a turbo-supercharged MK4R-C Kasei 23c engine, with the turbo-supercharger mounted behind the cockpit (itself made wider). This doubled the altitude at which the engine could produce its rated power, from 15,750ft up to 30,185ft. The J2M4 carried two extra oblique firing 20mm cannon, installed for use against high flying American B-29 bombers. Two prototypes were completed, but the turbo-supercharger proved troublesome, and no further aircraft of this type were produced.
J2M5 Model 33
The J2M5 was a second attempt to improve the high-altitude performance of the aircraft. It used the same airframe as the J2M4, but was powered by a MK4U-A Kasei 26a engine with a three-stage mechanical supercharger. Thirty four were built.
J2M5a Model 33a
The J2M5a would have been armed with four 20mm Type 99 Model 2 cannon. None were built.
J2M6 Model 31
The single prototype J2M6 was based on the J2M3, but with a new domed cockpit canopy. The designation Model 31 suggests that production versions would have used the fuselage of the J2M4.
J2M7 Model 23
The J2M7 would have been a version of the J2M3 but using the Kasei 26a with its three-stage mechanical supercharger. None were built.
J2M7a Model 23a
The J2M7a would have be similar to the J2M7 but with four Type 99 Model 2 cannon. None were built.
Models
| Model 11 | J2M2 |
Kasei 23a |
Model 21 |
J2M3 |
Kasei 23a |
Model 21A |
J2M3a |
|
Model 23 |
J2M7 |
Kasei 26a |
Model 23a |
J2M7a |
Kasei 26a |
Model 31 |
J2M6 |
|
Model 31a |
J2M6a |
|
Model 33 |
J2M5 |
Kasei 26a |
Model 33A |
J2M5a |
|
Model 34 |
J2M4 |
Kasei 23c |
Specifications J2M3
Engine: Mitsubishi MK4R Kasei 23a radial engine
Power: 1,820hp
Crew: 1
Wing span: 35ft 5.25in
Length: 32ft 7.75in
Height: 12ft 11.5in
Empty Weight: 5,423lb
Maximum take-off Weight: 8,695lb
Max Speed: 370mph at 19,360ft
Service Ceiling: 38,385ft
Range: 655 miles
Armament: Four 20mm cannon
Bomb-load: Two 132lb bombs
J2M Raiden and N1K1/2 Shiden/ Shiden-Kai Aces, Yasuho Izawa with Tony Holmes.
Looks at the limited careers of three late Japanese Navy interceptors of the Second World War, tracing their development and performance in combat. Includes an interesting account of the combat record of the 343rd Kokutai under Genda Minoru, a late war Japanese leader who didn't believe that the kawikaze ramming attack was the best way to attack American bombers. [read full review]
