One of the better fighter designs operated by the Imperial Japanese Navy in World War Two but not built in enough numbers, was the Mitsubishi J2M Raiden (“Thunderbolt” – Allied Code Name: Jack) land based interceptor used to attack Allied bombers such as the USAAF Boeing B-29 Superfortress. It was designed to be fast with a top speed 596km/h (370 mph – examples captured and tested by the United States using 92 octane fuel plus methanol, flew at speeds between 655km/h and 671km/h!), with an excellent rate of climb, to quickly reach the enemy bombers at altitude and later variants packed a punch with 4 x 20mm Type 99 wing mounted cannons to bring them down. It was armoured but maneuverability was sacrificed for speed and this pilot protection. Unfortunately performance at high altitude was hampered by the lack of an engine turbocharger on the main production Raiden aircraft.
Although a fast and well armed design, only 671 were built. The first J2M1 prototype flew on March 20th, 1942 (8 were built – they were armed with 2 x 7.7mm machine guns above the engine and 2 x 20mm Type 99 cannons in the wings) but production was delayed due to issues with the 14 cylinder Mitsubishi Kasei 13 radial engine cooling system (it used an air driven fan to blow cool air onto the engine) and a troublesome undercarriage design. The first J2M2 Model 11 variants, armed as per the prototypes reached development units in December 1942 but the engine problems delayed testing and more J2M2 production examples did not reach the operational 381st Kōkūtai until December 1943 – by then the tide of war had well and truly turned against Imperial Japan and Allied bombing soon reduced production by hitting aircraft parts and engine factories. The engine issues were partially overcome by using a Kasei 23a radial engine that had an inbuilt fan cooling system.
Developed in conjunction with the J2M2 was the J2M3 Model 21 variant that was armed with 2 x 20mm Type 99-1 outboard wing mounted cannons and 2 x 20mm Type 99-2 inboard wing mounted cannons. The first J2M3 entered service in October 1943 for testing but did not enter operational service with frontline squadrons until February 1944. Again all too late to turn that ever-present tide of incoming Allied forces.
A small number of J2M Raiden interceptors were used in combat during the Battle of the Philippine Sea in 1944 but saw limited success. Based off captured British examples the Imperial Japanese Navy must have operated the type in Malaya and they were also deployed in Korea but it was in the defence of the home islands in Japan where it saw its main use attempting to intercept the USAAF Boeing B-29 Superfortress bombers (as mentioned earlier the lack of a supercharger limited its performance though) – the cannon armament and diving tactics brought down some bombers but when the USAAF switched to night bombing its effectiveness was even further reduced as the Raiden was not fitted with radar. A lack of numbers also did not help the strategy to stop the Allied bombing offensive.
A small number of J2M4 and J2M5 were produced with Kasei 23c and Kasei 26a engines that had a turbo-supercharger to improve high altitude performance. The J2M4 had two upward firing 20mm cannons and the supercharger was fitted behind the cockpit but this proved unreliable, hence only 2 prototypes were built. Modifications were made to the J2M5 and a three stage turbo-supercharger was fitted to the engine – 34 of this variant were produced.
A number of Mitsubishi J2M Raiden aircraft were captured by the Allies and tested by the Americans and the Brits at the end of the war. In some cases Japanese pilots were used to fly the aircraft under close supervision (they knew the aircraft)! Technical Air Intelligence Units (TAIU) made up of USAAF, US Navy & RAAF personnel tested captured aircraft in the Pacific Theatre – initially set up in Australia in 1943, by 1945 they were in operation in the Philippines and tested at least one captured J2M Raiden. The general assessments seemed to be impressed with the rate of climb of the J2M.
The sole Mitsubishi J2M Raiden (Jack) survivor, a J2M3 variant (Serial Number 3014) is in the United States and can be found at the Planes of Fame Air Museum in Chino, California. I first saw this impressive looking fighter in person at Chino in 2013. I have not been able to find much information about this aircraft, the information sign at the museum was more about specifications and the museum website doesn’t have any background info but it must have been one of the aircraft tested by the Technical Air Intelligence Unit (TAIU). The livery and markings on the aircraft are a little confusing though, as the twin yellow lightning bolts on the fuselage are like those seen on Imperial Japanese Navy 352nd Kōkūtai (352nd Naval Air Group) Raiden aircraft but the tail number is more like those from the 302nd Kōkūtai (302nd Naval Air Group)! Perhaps they were just taking an each way bet?!