The J2M1 Raiden (Thunderbolt) was conceived to meet an Imperial Navy requirement for a shore-based Kyokuchi Sentoki, or Local [defence] Interceptor, usually abbreviated to Kyokusen. Al-though a 14-Shi (1939) requirement, the definitive specifica-tion for the Kyokusen was not formulated until April 1940, design being undertaken by Jiro Horikoshi assisted by Yoshitoshi Sone and Kiro Takahashi.
The Japanese navy's emphasis upon speed and climb rate prompted the designer Jiro Hinkoshi to adopt a squat single-engine design with long-chord radial engine cowling, and high-raked, curved windscreen. Of all metal construc-tion with a low aspect ratio laminar flow wing, the J2M1 was powered by a 14-cylinder Mitsubishi MK4C Kasei 13 radial rated at 1,430 hp for take-off and which, in order to reduce aerodynamic drag, drove the propeller via an extension shaft, a fan drawing cooling air through a narrow annular intake. Armament comprised two 7,7-mm and two 20-mm guns. The first of three J2M1 prototypes flew on 20 March 1942, but the test programme was plagued with technical difficulties and service test pilots were critical of some of its characteristics. Consequently, Mitsubishi was instructed to introduce numerous changes as the Kyokusen-Kai, or J2M2, these being introduced on the fourth of 14 experimental airframes that had been laid down.
On 13 October 1942, the fourth Kyokusen prototype was flown as the J2M2, this embodying numerous changes. The most noticeable external change was the replacement of the ex-tremely shallow, curved windscreen by one of deeper, more conventional form, with a suitably enlarged canopy and raised aft fuselage decking. The MK4R-A Kasei 23Ko drove a four-rather than three-bladed propeller via a shorter extension shaft, this engine benefiting from water-methanol injection and affording 1,800 hp for take-off. Individual exhaust stacks were introduced, fuel tankage was rearranged, and the pilot’s seat was moved both forward (2.75 in/70 mm) and upward (3.15 in/80 mm). In this form, the Kyokusen, or J2M2, was adopted as the Navy Interceptor Fighter Raiden (Thunder-bolt) Model 11, armament remaining as for the J2M1.
Production J2M2 fighters left the factory slowly and entered service with the 381st Kokutai late in 1943.
In the event, only eight J2M2 (Model 11) Raidens were built as this version was overtaken by the J2M3 (Model 21) characterised with a stronger wing stressed to mount an armament of four wing-mounted 20-mm cannon, this thus becoming the first service Raiden, the J2M3-Ko (Model 2lKo) differing in the type of cannon installed. The heavier armament now restricted the performance of the Raiden to the extent that it no longer met the original demands, and the J2M4 was an attempt to restore the performance by including a turbocharger.
The J2M4 had a Kasei 23Hei engine with a turbosuper-charger and two of the wing cannon transferred to the fuselage to fire at an oblique angle. The first of three prototypes of the J2M4 flew on 24 September 1944, but persistent difficulties with its turbosupercharger led to its discontinuation.
The J2M5 (Model 33) and J2M6 (Model 31) were developed in parallel, entering flight test in May and June 1944 respectively and both being committed to production. Whereas the J2M6 differed from the J2M3 essentially in having a wider and taller windscreen, the basic model reverting to J2M2 armament and the J2M6-Ko (Model 3lKo) having four wing cannon, the J2M5 had a 1357kW Kasei 26Ko engine equipped with a mechanically-driven three-stage supercharger. This latter was ordered into production with the Takaza Arsenal and Nihon Kentetsu, as well as Mitsubishi. The J2M5 (34 built) achieved 382 mph (615 km/h) at 22,310 ft (6 800 m.
In all, 476 J2Ms were built. The Allies selected the reporting name 'Jack' for the J2M.
Engine: Mitsubishi MK4C Kasei 13 radial, 1,430 hp
Max speed, 359 mph (577 km/h) at 19,685 ft (6 000 m)
Empty weight, 4,830 lb (2 191 kg)
Normal loaded weight, 6,307 lb (2 861 kg)
Span, 35 ft 5¼ in (10,80 m)
Length, 32 ft 5¾ in (9,90 m)
Height, 12 ft 6 3/8 in (3,82 m)
Wing area, 215.82 sq ft (20,05 sq.m)
Armament: two 7,7-mm and two 20-mm guns
Engine: MK4R-A Kasei 23Ko, 1,800 hp
Engine: 1 x Mitsubishi "Kasei-23a", 1350kW
Max take-off weight: 3435 kg / 7573 lb
Empty weight: 2460 kg / 5423 lb
Wingspan: 10.8 m / 35 ft 5 in
Length: 9.95 m / 32 ft 8 in
Height: 3.95 m / 12 ft 12 in
Wing area: 20.05 sq.m / 215.82 sq ft
Max. speed: 580 km/h / 360 mph
Ceiling: 11700 m / 38400 ft
Range: 1900 km / 1181 miles
Armament: 4 x 20mm cannons, 120kg of bombs
J2M3 (Model 21)
Max speed, 363 mph (584 km/h) at 17,880 ft (5 450 m)
Initial climb, 3,838 ft/min (19,50 m/sec)
Normal range, 655 mls (1055 km)
Empty weight, 5,489 lb (2490 kg)
Loaded weight, 7,584 lb (3440 kg)
Span, 35 ft 5¼ in (10,80 m)
Length, 32 ft 7½ in (9,94 m)
Height, 12 ft 11¼ in (3,94 m)
Wing area, 215.82 sq ft (20,05 sq.m)\Armament: four wing-mounted 20-mm cannon
Engine: Kasei 23Hei.
Engine: Kasei 26Ko
Max speed: 382 mph (615 km/h) at 22,310 ft (6 800 m)
Mitsubishi J2M Raiden