Illustrated by Shigeo Koike.
There were some early attempts to produce a long range bomber - for example, the Mitsubishi G7M1 Taizan (a 16-shi project) - plus designs that were actually built such as the Nakajima G5N Shinzan and Nakajima G8N Renzan. The Shinzan was not a success and the Renzan failed to reach operational service as a combat aircraft, let alone reach America and return.
The DC-4E was sold by Douglas to Japan's Mitsui Trading Company, Ltd. for Japan Air Lines Company, Ltd.; no more are built. The Japanese pay $950,000 for the airplane, which is shipped to Tokyo by sea on September 29. After it is reassembled by Douglas technicians, the Super Mainliner will be the model for that nation's first four-engine land plane, the unsuccessful Nakajima G5N bomber/transport Shinzan (Mountain Recess).
The design that emerged from this study was for an all-metal mid-wing monoplane with fabric-covered control surfaces and powered by four 1,870 hp Nakajima NK7A Mamori 11 air-cooled radial engines driving four-bladed propellers. Notable features included a long ventral bomb-bay, glazed nose and twin tailfins replacing the DC-4E's distinctive triple rudder. The DC-4E's retractable tricycle undercarriage was retained, as well as the original wing form and powerplant arrangement. Defensive armament comprised one 20mm Type 99 Model 1 cannon each in a power-operated dorsal and tail turret plus single-mount hand-operated 7.7mm Type 92 machine guns in the nose, ventral and waist positions.
The first prototype G5N1 made its maiden flight on 14:35 8 April 1941. Overall performance proved disappointingly poor however, due to a combination of excessive weight, the unreliability of the Mamori engines and the complexity of the design. Only three more prototypes were completed. In an attempt to salvage the project, two additional airframes were fitted with 1,530 hp Mitsubishi MK4B 12 "Kasei" engines and redesignated G5N2s. Although the Mitsubishi engines were more reliable than the original Mamori 11s, the aircraft was now even more hopelessly underpowered and further development of the type was halted.
Of the six completed Shinzans, four of them were relegated for use as long-range Navy transports under the designation G5N2-L Shinzan-Kai Transport. The Allies allocated the code-name "Liz" to the aircraft, in the expectation it would be used as a bomber.
Z Superbombers Project (1942-1944)
Similar to the Nazi ‘Amerika-Bomber’ project to develop long-range strategic bomber to strike the United States from Germany, Japan initiated the ‘Project Z’ to develop an intercontinental bomber to strike North America. The Japanese were desperate to develop something like the US B-29 Superfortress long-range heavy bomber which was introduced in 1944.
Imperial Japanese Navy had designed the four-engined ‘Nakajima G5N’ heavy bomber prior to the Second World War and introduced it in 1941. But their planners wanted something much larger, faster, heavier and capable of flying at 32,800 feet with a load of 22 one thousand pound bombs; B-29 Superfortress also had similar capabilities with a speed up to 350 mph during wartime. Imperial Japanese Army was presented several designs for the Project Z; these included- the Nakajima G10N Fugaku and Kawasaki Ki-91. Fugaku means Mount Fuji. G10N Fugaku was supposed to have a wingspan of 213 ft 2 in and a total length of 147 ft 7in. It would have been powered by six 5,000 hp engines and capable of reaching speeds of 365 mph at 25,000 ft. Nakajima Aircraft Company started developing G10N’s 4 row 36 cylinder 5,000 hp engines in 1943 but abandoned due to complexity. Z Superbombers Project was cancelled in July 1944.