The C6N originated from a 1942 Imperial Japanese Navy specification for a carrier-based reconnaissanceplane with a top speed of 350 knots (650 km/h) at 6,000 m and range of 2,500 nautical miles (4,960 km). Nakajima's initial proposal, designated N-50, was for a craft with two 1,000 hp (750 kW) engines housed in tandem in the fuselage, driving two propellers mounted on the wings. With the development of the 2,000 hp (1,500 kW) class Nakajima Homare engine, the dual powerplant configuration was abandoned and Nakajima decided on a more conventional single-engine layout. Unfortunately the new Homare's power output was less than expected, and the design had to be optimized in other areas. The resulting aircraft was designed around a long and extremely narrow cylindrical fuselage just large enough in diameter to accommodate the engine. The crew of three sat in tandem under a single canopy, while equipment was similarly arranged in a line along the fuselage. The C6N's low-mounted laminar flow wing housed fuel tanks and was fitted with both Fowler and slit flaps and leading-edge slats which lowered the aircraft's landing speed to ease use aboard aircraft carriers. Like Nakajima's earlier B6NTenzan torpedo bomber, the vertical stabilizer was angled slightly forward to enable tighter packing on aircraft carrier decks.
The C6N's first flight was on 15 May 1943, with the prototype demonstrating a speed of 639 km/h (345 kn; 397 mph). Performance of the Homare engine was disappointing, especially its power at altitude, and a series of 18 further prototypes and pre-production aircraft were built before the Saiun was finally ordered into production in February 1944.
Although designed for carrier use, by the time it entered service in September 1944 there were few carriers left for it to operate from, so most C6Ns were flown from land bases. Its speed was exemplified by a telegraph sent after a successful mission: "No Grummans can catch us." ("我に追いつくグラマンなし"). The top speed of the Hellcat was indeed of the same level, so overtaking a Saiun was out of the question.
A total of 463 aircraft were produced. A single prototype of a turbocharged development mounting a 4-blade propeller was built; this was called the C6N2 Saiun-kai. Several examples of a night fighter version C6N1-S with oblique-firing (Schräge Musik configuration) single 30 mm (or dual 20 mm) cannon were converted from existing C6N1s. As Allied bombers came within reach of the Japanese home islands, a first class night fighter was required. This led Nakajima to develop the C6N1-S by removing the observer and replacing him with two 20 mm cannons. The C6N1-S's effectiveness was hampered by the lack of air-to-air radar, although it was fast enough to enjoy almost complete immunity from interception by Allied fighters. A torpedo carryingC6N1-B was also proposed, but was not needed after most of Japan's aircraft carriers were destroyed.
Despite its speed and performance, on 15 August 1945 a C6N1 happened to be the last aircraft to be shot down in World War II. Just five minutes later, the war was over and all Japanese aircraft were grounded.
Nakajima C6N1-S night fighter variant. Note the obliquely mounted 30 mm cannon in the fuselage.
Three prototypes and sixteen supplementary prototypes produced, four-blade propeller; latter batch were equipped three-blade propeller, mounted Nakajima NK9K-L Homare 22 engine, No. 6 was mounted Nakajima NK9H Homare 21 engine. Renamed Test production Saiun (試製彩雲, Shisei Saiun) in July 1943.
C6N1 Saiun Model 11 (彩雲11型, Saiun 11-gata)
General production model. Three-blade propeller, mounted Nakajima NK9H Homare 21 engine.
C6N1 Saiun Model 11 night fighter variant (彩雲11型改造夜戦, Saiun 11-gata Kaizō yasen)
Temporary rebuilt two-seat night fighter version; this was not a regulation naval aircraft. Development code C6N1-S was not discovered in the IJN official documents. One model with a singular 30 mm Type 5 cannon and at least five models with ×2 20 mm Type 99-1 cannon were converted from standard C6N1 models. One surviving example of the ×2 20mm cannon variant is stored in the Paul E. Garber Preservation, Restoration, and Storage Facility.
C6N2 Test production Saiun Kai/Saiun Model 12 (試製彩雲改/彩雲12型, Shisei Saiun Kai/Saiun 12-gata)
Fitted with four-blade propeller, 1,980-hp (1,476-kW) Nakajima NK9K-L Homare 24-Ru turbocharged engine. Two prototypes were converted from regular C6N1 models in February 1945.
C6N3 Test production Saiun Kai 1 (試製彩雲改1, Shisei Saiun Kai 1)
Proposed high-altitude night fighter version of the C6N2. Dual 20 mm cannons were installed. Only a project.
C6N4 Test production Saiun Kai 2 (試製彩雲改2, Shisei Saiun Kai 2)