Nakajima J1N Gekko (Moonlight) 'Irving'

The Nakajima J1N, allied code name 'Irving', was originally designed as a long range fighter aircraft for operations over China, but entered service as a long-range reconnaissance aircraft and later became a night fighter, when it was known as the Gekko (Moonlight).

Development

Soon after the outbreak of the Second Sino-Japanese War the Japanese Navy began to discover the difficulties of fighting in such a vast country. Their bombers were being forced to operate beyond the range of the existing single-seat fighters (in particular the Mitsubishi A5M Navy Type 96 Carrier Fighter). They believed that the answer was a long-range fighter that could escort the bombers all the way to their targets.

In 1938 the Japanese Navy issued a specification for the new fighter. It was to be a three-seat twin-engined aircraft with a normal range of 1,496 miles, a top speed of 322mph. the manoeuvrability to cope with single-seat fighters and an armament of fixed forward firing 20mm cannon and 7.7mm machine guns and rear-firing flexibility mounted guns. The overall specification was influenced by the French Potez 63, but even the Potez 631, the best fighter variant to see service before the fall of France, only had a top speed of 275mph and a range of 758 miles.

The Nakajima design team was led by Katsuji Nakamura. It produced a low-wing monoplane with a clean fuselage. The prototype was powered by contro-rotating 1,130hp Nakajima Sakae radial engines (the Sakae 21 and Sakae 22). One 20mm cannon and two 7.7mm machine guns were mounted in the nose. The rear firing guns were carried in an experimental housing - two hydraulically powered remote controlled barbettes, each carrying two 7.7mm guns, were mounted behind the cockpit.

The J1N1 prototype made its maiden flight in May 1941. Manoeuvrability was poor and so the second prototype was given leading-edge wing slots. Service trials began in August 1941, and the J1N1 soon proved to be disappointing. The contra-rotating engines caused problems, the experimental barbettes were both too heavy and too difficult to aim. The modified aircraft was very manoeuvrable for a two-engined aircraft, but not good enough to cope with single-seat fighters. In competitive trials against the Mitsubishi A6M2 the Nakajima aircraft came off badly, coming second in everything but range. The Zero still had an impressively long range for a single-seat fighter, and so in October 1941 the J1N1 was rejected as a fighter. 

J1N1-C/ J1N1-R Navy Type 2 Reconnaissance Aircraft

Although the J1N1 had been rejected as a fighter, the Japanese Navy realised that its combination of long range and good top speed would make it a useful reconnaissance aircraft. Nakajima already had a number of further fighter aircraft under construction, and they were ordered to complete them as the prototypes for a possible reconnaissance aircraft.

Nakajima concentrated on reducing weight and improving reliability. Weight was reduced by removing all of the guns, including the complex barbettes, and by reducing the internal fuel capacity by 125 gallons. Two 72.6 gallon drop tanks could be carried under the wings and a flexibly mounted rear-firing 13mm Type 2 machine gun was added.

The fuselage was redesigned, splitting the cockpit into two. The pilot and radio operator/ gunner set in the forward cockpit, while the navigator/ observer had a separate position just behind the wing trailing edge.

Reliability was improved by replacing the contra-rotating engines with two Sakae 21 engines.  

The J1N1-C was accepted for production in July 1942 as the Navy Type 2 Reconnaissance Plane. Fifty-four were produced between April 1942 and March 1943, and the type was introduced into service in the autumn of 1942. When the Allies first sighted the J1N1-C over the Solomon Islands it was misidentified as a fighter, and thus given the male code name 'Irving'. The aircraft was later redesignated as the J1N1-R. In some aircraft the 13mm gin was replaced with a 20mm cannon mounted in a spherical turret.

J1N1-C KAI Night Fighter prototype

In the spring of 1943 the commander of a unit based on Rabaul, Yasuna Kozono, suggested that the J1N1-C could be used as a night fighter. A single aircraft was modified to test out his idea. Four 20mm cannon were mounted in the observer's position, two firing up and forward at 30 degrees and two firing down and forwards. This prototype, with the designation J1N1-C KAI, successfully shot down two B-24 Liberators, and the Navy decided to order the night-fighter variant into production.

J1N1-S Gekko Night Fighter

The night fighter entered production as the J1N1-S Gekko Model 11 in August 1943. Early production aircraft carried the same four guns as the prototype. The rear fuselage was modified to smooth out the step behind the old observer's cockpit. Some carried a small searchlight in the nose and others were given AI radar.

The night fighter was produced in much larger numbers than the reconnaissance aircraft - 183 J1N1s were built between April 1943 and March 1944 and another 240 between April 1944 and the end of production in December 1944. Most of these aircraft were fighters. Total production of all types was 479.

J1N1-Sa Gekko Model 11

The J1N1-Sa only carried the two upward firing guns - the downward firing guns were rarely used during interceptions of American bombers and so were thus useless weight. Most of the J1N1-Sa carried the AI radar. Some aircraft had a 20mm cannon installed instead of the radar or searchlights. 

J1N1-Sa Gekko Model 11 Ko

In combat the J1N1-S proved to be quite effective against the B-24 Liberator, but the B-29 Superfortress was too fast for it - the J1N1-S was normally only able to make a single attack on each bomber before it was out of range, and that was rarely enough to take down the well protected B-29. As with many Japanese types most of the surviving aircraft were used in kamikaze attacks during 1945, normally carrying two 551lb bombs.

J1N1-S
Engine: Two Nakajima Sakae 21 radial engines
Power: 1,130hp each
Crew: 2
Span: 55ft 8.25in
Length: 41ft 10.75in
Height: 13ft 1.5in
Empty weight: 10,692lb
Maximum take-off weight: 18,045lb
Max speed: 315mph at 19,030ft
Service ceiling: 30,580ft
Range: maximum 2,348 miles, normal 1,581 miles
Armament: Four 20mm cannon, two obliquely upwards mounted and two obliquely downwards mounted

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How to cite this article: Rickard, J (25 September 2013), Nakajima J1N Gekko (Moonlight) ‘Irving’ , http://www.historyofwar.org/articles/weapons_nakajima_J1N_gekko.html

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