Background

The Kawanishi N1K2-J Shiden Kai (Violet Lightning Modified) is generally rated as being one of the finest land-based fighter planes fielded by the Japanese during the Pacific War. It was actually superior to most of the carrier-based US Navy fighters that opposed it, and could even hold its own against the later models of the P-51 Mustang. Unfortunately for the Japanese, the aircraft was available too late and in insufficient numbers to affect the outcome of the war. The N1K2-J had a rather curious evolution. It actually originated from a floatplane fighter designed for offensive operations, and evolved in stages to produce what was perhaps the finest land-based fighter plane available to any of the combatants in the Pacific War.

N1K1 Kyofu (Mighty Wind) Fighter Floatplane

In 1940, anticipating a coming war in which Japan would be involved in far-ranging offensive operations, the Japanese Navy issued a requirement for a floatplane fighter which could be used for offensive operations in forward areas were no airfields existed. In response to this requirement, the Nakajima Hikoki K. K. concern at Koizumi offered a design based on a modified Mitsubishi A6M2 Reisen carrier-based fighter. This eventually emerged as the A6M2-N and was given the Allied code name Rufe when it entered service. However, this aircraft was considered as only an interim solution, and the Kawanishi Kokuki K. K. of Naruo was instructed to begin work on a more-advanced aircraft specially designed for the purpose. The Japanese Navy issued a 15-Shi specification (so named for the 15th year of the Showa era, which was 1940) for this aircraft in September of 1940.

A team of engineers at the Kawanishi plant including Toshihara Baba, Shizuo Kikuhara, Hiroyuki Inoue, and Elizaboro Adachi came up with a design for a compact aircraft with mid mounted wings of laminar-flow section. A single large float was to be installed underneath the fuselage, with auxiliary floats being carried underneath each outer wing. The central float was to be attached to the fuselage by a forward V-strut and an I-strut at the rear. The initial design had the auxiliary floats being retractable and with metal planing bottoms and inflatable rubberized-fabric tops. However, these retractable floats were deemed to be too heavy and complex, and were replaced by fixed cantilever floats prior to the first flight of the prototype. The aircraft was to be powered by a 1460 hp Mitsubishi MK4D Kasei 14 air-cooled radial driving a pair of contra-rotating two-bladed propellers. The contra-rotating propellers were intended to offset the high propeller torque on takeoff expected from such a powerful engine mounted in a relatively small airframe.

The first N1K1 prototype took off on its first flight on May 6, 1942. The contra-rotating propellers of the prototype were later dropped as being too complex, and the design was modified to accept a 1460 hp MK4C Kasei 13 (Ha.32/13) radial engine driving a single conventional three-bladed propeller via an extension shaft. The single propeller installation was simpler and less mechanically troublesome, but it did produce (as expected) an extremely powerful torque on takeoff that required considerable skill on the part of the pilot to counter.

Armament consisted of two 20-mm Type 99 Model 1 cannon and two 7.7 mm (0.303 in) machine guns.

Once in the air, the N1K1 was found to be an extremely pleasant aircraft to fly and it had remarkable manoeuvrability by virtue of its combat flaps. The Japanese Navy accepted the design under the designation N1K1 Navy Fighter Seaplane Kyofu (Mighty Wind) Model 11, and production began.

Service trials aircraft were delivered to the Japanese Navy starting in August of 1942. Early production aircraft were powered by 1460 hp MK4C Kasei 13 engines, but later production aircraft were powered by 1530 hp MK4E Kasei 15 engines which differed only in minor details. 

The Kyofu entered service with the Japanese Navy in July of 1943, and was assigned the Allied code name "Rex". Production was slow in gearing up and by December of 1943, it had reached only 15 aircraft per month.

However, by the time that the Kyofu entered service, Japan had been thrown back onto the defensive, and the Kyofu was never to serve in the offensive fighter role for which it had been designed. Instead, the the N1K1 was assigned as an interceptor based at Balikpapan in Borneo, a role for which it had never been intended. Even though the Kyofu was a rugged and efficient floatplane, it was no match for the single-seat Allied fighters which opposed it. Consequently, production of the Kyofu was terminated in March of 1944 after the delivery of only 89 production aircraft. Also abandoned at the same time was the N1K2-I Kyofu-Kai project, to have been powered by the improved 1900 hp Mitsubishi MK4R Kasei 23 engine.

Later in the war, one Kyofu unit was assigned as an interceptor with the Otsu Kokutai operating from the inland Lake Biwa on the Japanese home island of Honshu.

Specification of the Kawanishi N1K1 Kyofu Floatplane

Powerplant: One Mitsubishi MK4E Kasei 15 fourteen-cylinder air-cooled radial rated at 1530 hp for takeoff, 1400 hp at 8530 feet, 1280 hp at 19,685 feet.

Performance: Maximum speed 302 mph at 18,700 feet, service ceiling 34,645 feet cruising speed 230 mph at 6560 feet. Climb to 16,400 feet in 5 minutes 32 seconds. Normal range 660 miles, maximum range 1040 miles.

Weight: 6,067 pounds empty, 7,716 pounds loaded, 8,184 pounds with maximum loadout.

Dimensions: wingspan 39 feet 4 7/16 in, length 34 feet 8 7/8 in, height 15 feet 7 in, wing area 252.95 square feet.

Armament: Two 7.7 mm (0.303 in) Type 97 machine guns in the fuselage and two 20-mm Type 99 Model 1 cannon in the wings. Two 66 lbs bombs could be carried externally.

N1K1-J Shiden (Violet Lightning)

In December of 1941, the Kawanishi engineering team proposed to their management that it might be a good idea to produce a land-based version of the company's N1K1 Kyofu seaplane fighter. Kawanishi management thought enough of the idea that they decided to go ahead with the project as a private venture.

Initially, few changes over the N1K1 were planned other than the replacement of the floats with retractable land undercarriage. However it was decided to replace the 14-cylinder Kasei engine with an eighteen-cylinder Nakajima Homare air-cooled radial which, it was hoped, would deliver 2000 hp. To take advantage of the increased power, a new four-bladed propeller with a diameter of 10 feet 10 inches was to be fitted. However, since the original mid-wing configuration of the Kyofu was retained, a very stalky undercarriage was required in order that the prop be able to clear the ground. This in turn required a rather complex scheme of double landing gear retraction, in which the legs contracted as they folded into the wing wells. The aft portion of the fuselage was deepened to give more vertical stabilizing area and included a retractable tailwheel.

A unique feature of the N1K1-J was its set of combat flaps. Whereas flap extension was manually controlled on the Kyofu seaplane, the flaps on the landplane version had the ability automatically to change their angle in response to changes in g-forces during manoeuvres. This automatic operation freed up the pilot from having to worry about his flaps during combat, and eliminated the possibility of a stall at an inopportune time.

The land based fighter made its maiden flight on December 27, 1942. Since the aircraft was a private venture, it had no military designation, and was known as the Model X-1 experimental land based fighter by the manufacturer. The engine was the 1820 hp Nakajima Homare 11 radial. It was armed with two 7.7 mm Type 97 machine guns in the fuselage and two 20-mm Type 99 Model 2 cannon housed in underwing gondolas.

Since the Homare 11 had been accepted for production before the completion of its final tests, it was plagued with teething troubles. The early Homare engine failed to develop its rated power, the propeller torque during takeoff was excessive, and the visibility during taxiing was poor. However the aircraft had pleasant flying characteristics and the automatic combat flaps gave the aircraft exceptional manoeuvrability.

By July of 1943, four prototypes had been built, and one was handed over to the Navy for trials. The performance was disappointing, the maximum speed being only 357 mph (403 mph had been promised). However, it was faster than the Mitsubishi A6M5 Reisen and was more manoeuvrable and longer-ranged than the faster Mitsubishi J2M2 Raiden. By this time, the Japanese Navy was in desperate need of fighters capable of countering the Vought F4U Corsair and the Grumman F6F Hellcat, and gave authorization for Kawanishi to proceed with further development of the land-based version of the Kyofu under the designation N1K1-J Shiden (Violet Lightning) Interceptor Fighter. The J indicated that it was a landplane development of the original N1K1.

Further prototypes and service trial aircraft were built during 1943. They were fitted with the more powerful 1990 hp Nakajima NK9H Homare 21 radial. The cowling was modified and featured an additional lower lip scoop. Individual exhaust stacks were fitted, and an external oil cooler was mounted on the port side of the cowling behind and below the cooling gills. Two additional 20-mm Type 99 Model 2 cannon were installed in the wings just outboard of the external underwing cannon gondolas.

Quantity production was ordered by the Navy as the Navy Interceptor Fighter Shiden Model 11. By the end of 1943, 70 aircraft had been built at the Naruo Works, and the first aircraft had been delivered by the Kawanishi plant at Himeji.

The N1K1-J entered service with land-based squadrons of the Japanese Navy early in 1944. Armament consisted of 2 7.7-mm machine guns in the fuselage and four 20 mm cannon in the wings (2 in the wing, 2 in underwing gondolas). The first large unit of Shidens to be deployed was the 341st Kokutai (Air Corps), which was transferred to Luzon from Formosa on October 20, 1944. The N1K1-J was first encountered by American forces in combat over Formosa and the Philippines. It was assigned the Allied code name George. It quickly established itself as one of the toughest and most troublesome Japanese fighters yet to be met in combat. It was a truly exceptional combat aircraft in the hands of an experienced pilot. It proved itself superior to most US shipboard fighters that it encountered, and many experienced Shiden pilots regarded the previously-formidable Grumman F6F Hellcat as a particularly easy "kill".
 

The N1K1-J was, however, not without its faults. Operations were plagued by frequent undercarriage malfunctions, the complex double-retraction landing gear causing lots of problems. Aircraft availability was frequently limited by insufficient maintenance crews and by logistics problems. The Homare engine was rather unreliable and was a maintenance headache. The wheel brakes were so bad that most pilots chose to land their Shidens on the grass alongside the runway in order to shorten the landing run.

The N1K1-Ja Model 11A differed from the Model 11 in having all four of its 20-mm cannon inside the wing, and it dispensed with the fuselage-mounted machine guns. The N1K1-Jb Model 11B had four improved 20-mm cannon in the wing, was fitted with two underwing racks for bombs of up to 550 pounds in weight, and late production N1K1-Jb fighters had completely redesigned, square-tipped vertical tail surfaces. The N1K1-Jc Shiden Model 11C was a specialized fighter-bomber version similar to the Model 11B but with four underwing bomb racks. At least one N1K1-J used in the Philippines was captured by US forces. It was repaired and tested by American Technical Air Intelligence Unit pilots at Clark Air Base. The respect that American pilots had for the airplane was found to be fully justifiable.

Following the fall of the Philippines to US forces, the Shiden was met in large numbers during the invasion of Okinawa. A Japanese military communique reported an engagement in which a unit of 34 Shidens met a force of 70 Allied fighters, destroying 20 of them against a loss of only twelve of their number. Shidens also equipped the 343rd Kokutai the First Air Fleet based at Tinian, and were later based at Shikoku in Japan in defense of the home islands during the spring of 1945.

Late in 1944, a Shiden was modified as the N1K1-J-Kai with a supplementary rocket unit to increase power for short periods. The rear portion of the fuselage was modified to house a rocket motor. Several aircraft received this modification, but the conversion never achieved operational status.

The Shiden Special Attack aircraft was a variant capable of carrying out suicide attacks. In early 1945, four Shiden 11s were modified for this mission, but were never expended.

A total of 9 prototype and 520 N1K1-J production aircraft were built by the Naruo plant, and 468 N1K1-J production aircraft were built by the Himeji plant. This brought total production of the Shiden to 1007 examples, including prototypes. Production of the N1K1-J was phased out at the Narou plant in December 1944 in favour of the improved N1K2-J. Production of the N1K1-J at the Himjei plant was halted by the damage caused by B-29 raids.

Kawanishi N1K2-J Shiden of the 343rd Kokutai
 

N1K2-J Shiden Kai (Violet Lightning Modified)

Although the N1K1-J was an outstanding fighter, it did have some serious defects. Its Homare 21 engine was notoriously unreliable, and the complex doubly-retracting landing gear was subject to frequent failures. Even before the N1J1-J entered production, work had already begun at Kawanishi on correcting some of its more glaring defects, in particular its long and complex landing gear.

The result of these changes was the Shiden-Kai (Violet Lightning--Modified). Given the designation N1K2-J, the aircraft was completely redesigned so as to use fewer components in order to simplify its construction. More non-critical materials were to be used. Another step towards simplification involved the use of pre-formed sheet construction. Perhaps the most easily-noted innovation was the use of a low-mounted wing in place of the original mid-mounted wing. This permitted a shorter set of landing gear legs to be used, and the complex double-retraction system which had caused so many problems could be eliminated. In addition, the fuselage was lengthened and the tail surfaces were redesigned. The result was a virtually new aircraft, although the unreliable 1990 hp Homare 21 engine of the N1K1-J was retained. Armament was four 20-mm cannon, all mounted internally to the wing.

The first N1K2-J prototype took off on its maiden flight on December 31, 1943. It was handed over to the Japanese Navy for trials in April of 1944. Although the Homare 21 engine was still mechanically unreliable, the Navy liked the aircraft so much that they authorized quantity production of the N1K2-J to be its standard land-based fighter and fighter-bomber even before the service trials were completed. Production aircraft were designated Navy Interceptor Fighter Shiden Kai (Violet Lightning Modified) Model 21. In addition to the Kawanishi plant at Naruo, the Shiden Kai was ordered into production at the Himeji works of Kawanishi. Shiden Kai fighter aircraft were also ordered into production from the Dai-Nana Kokuki Seisakusho (7th Airframe Works) of the Mitsubishi Jukogyo K. K. at Tsurashima, from the Aichi Kokuki K. K. at Eitoku, from the Showa Hikoki K. K. at Shinonoi, and from the Naval Air Arsenals at Hiro, Omura, and Koza.

A further seven prototypes had been completed by June of 1944, However, the prototypes began to experience a long series of teething troubles, which proved difficult to correct. The Shiden-Kai program began to slip its schedules, and by the autumn of 1944 the N1K2-J production lines were beginning to experience shortages of vital components due to B-29 attacks against the factories of Kawanishi's subcontractors. By the end of 1944, only 60 Shiden Kais had been delivered by the Naruo factory, and production at Himeji did not begin until March of 1945. The other manufacturers in the Shiden Kai pool were never able to produce more than a handful of aircraft.
 

The Shiden Kai was to become perhaps the best all-round fighter to be operational in the Pacific theatre. It was fast, powerful, and maneuverable, and was well-armed and armoured. In the hands of an experienced pilot, the Shiden-Kai was the equal of any Allied fighter, even the later models of the P-51 Mustang which began to appear over Japan in the spring of 1945. In one notable action, on February 16 1945 over Yokohama, Warrant Officer Kinsuke Muto of the 343rd Kokutai in an N1K2-J single-handedly battled a dozen F6F Hellcats. He shot down four of them before the rest were forced to break off combat and return to their carrier. However, against the B-29, the N1K2-J was less successful, since its climbing speed was insufficient and the power of the Homare 21 engine fell off rather rapidly at higher altitudes.

A two-seat trainer version, the N1K2-K Shiden Kai Rensen (Violet Lightning Modified Fighter Trainer) was planned, but only a few examples were produced by fitting a second seat behind the pilot's seat of some existing N1K2-J airframes.

The Shiden Kai had its centre of gravity too far aft, and to correct this problem the N1K3-J Shiden Kai 1 Model 31 was built, which had the Homare 21 engine moved forward six inches. This freed up enough space to permit two 13.2-mm machine guns to be fitted in the engine cowling. Two prototypes were built at Himeji, but this model was never put into production.

The N1K3-A Shiden Kai 2 Model 41 was a carrier-based variant of the N1K3-J. It too was never put into production.

In an attempt to overcome some of the operational problems caused by the still unreliable Homare 21, the N1K4-J Shiden Kai 3 Model 32 and its carrier-borne variant the N1K4-A Shiden Kai 4 Model 42 were developed. These were powered by the 2000 hp NK9H-S Homare 23 fuel-injected radial. Two prototypes of the N1K4-J and one of the N1K4-A were built in the spring of 1945 at Naruo. The carrier-based aircraft was accepted for production as the Shiden 41, but was later abandoned since by that time Japan's carrier forces had been completely destroyed.

One of the weaknesses of the Shiden Kai was its rather lacklustre high-altitude performance. It had proven to be ineffective against the B-29 owing to its poor climbing ability. In search of better high-altitude performance, the N1K5-J Shiden Kai 5 Model 25 was planned, powered by a 2200-hp Mitsubishi MK9A eighteen-cylinder air-cooled radial. However, the sole prototype of the N1K5-J was destroyed prior to completion during a B-29 raid in June of 1945. Another high-altitude interceptor version of the Shiden Kai was to be based on a Homare 44 engine equipped with a three-speed mechanical supercharger. The end of the Pacific War brought an end to all these projects.

Only 415 production examples of the outstanding N1K2-J fighter were built, owing primarily to construction snags and delays resulting from the continuous B-29 raids on the Japanese homeland in the last year of the war. With the exception of Kawanishi's Naruo and Himeji plants, the other companies involved in the production pool were late in getting started and delivered only a token number of machines before the war ended. It is fortunate for the Allies that this outstanding aircraft was not available in greater quantity.
 

After the war in the Pacific was over, several N1K2-J fighters were discovered intact at Japanese airfields and were brought back to the United States for study. Several of these are now on display in museums or are awaiting restoration. 

(Navy Interceptor Fighter Shiden "Violet Lightning" - Kawanishi N1K2-J)

Allied Codename: (Kawanishi N1K2-J) George - (N1K1 Kyofu) - Rex

Type: Single Seat Land Based Fighter Interceptor

Powerplant: One 1,900 hp (1484 kw) Nakajima NK9H Homare 21 18-cylinder radial piston engine.

Performance: Maximum speed 370 mph (595 km/h) at 18,370 ft (5600 m); cruising speed 230 mph (370 km/h) at 9,845 ft (3000 m); service ceiling 35,300 ft (10760 m).

Range: 1,451 miles (2335 km) with a single drop tank.

Weight: Empty 5,858 lbs (2657 kg) with a maximum take-off weight of 10,714 lbs (4860 kg).

Dimensions: Span 39 ft 4 1/2 in (12.00 m); length 30 ft 8 in (9.35 m); height 13 ft 0 in (3.96 m); wing area 252.96 sq ft (23.50 sq m).

Armament: Four wing mounted 20 mm Type 99 Model 2 cannon, plus two 551 lbs (250 kg) bombs on underwing racks.

Variants: N1K1 Koyfu (naval floatplane), N1K1-J (land based prototype), N1K1-Ja (revised armament), N1K1-Jb (modified wing with the intent to carry cannon and rockets), N1K1-Jc (night fighter), N1K2-J (Navy Interceptor Fighter Shiden KAI), N1K2-K (two seat trainer), N1K3-J (two prototypes), N1K4-J (two prototypes), N1K4-A (carrier based), N1K5-J (single prototype destroyed while under production).