Heavy Bomber First flight: 1941 Nakajima

G5N Shinzan (Decay) . In the late 1930s, the aviation command of the Imperial Japanese Navy came to the conclusion that it was necessary to have a heavy bomber capable of solving strategic tasks. Realizing this, in 1938 Kaigun Koku Hombu formulated the 13-Si requirements for a new bomber, the flight range of which was to be of the order of 5556-6482 km (3000-3500 nautical miles). The only way to achieve such a range - along with an increased bomb load (2000-4000 kg) compared to the G3M and G4M - was to use a four-engine scheme.However, at that time, none of the Japanese aircraft manufacturers had the experience of building such large aircraft, and this is still more complicated an already very difficult task.

A way out of the situation was found in the USA, where two years earlier, Douglas specialists began working on a large four-engined long-range DC-4E passenger aircraft (not to be confused with the later DC-4 / C-54 Skymaster project) ... This aircraft, which lost in the competition to the Boeing B-307 and was built in a single copy, was bought by the civil airline "Japanese Airlines" by order and for the money of the fleet, allegedly for its own needs. After the assembly of the American aircraft delivered to Japan in disassembled form, it passed flight tests and was secretly transferred to the Nakajima company, which was instructed to develop a bomber project in accordance with the 13-C specification. It was prescribed to use the DC-4E design as a base.

The prototype G5N1, which became the first four-engined aircraft in the Japanese fleet, took off in April 1941. From the "American" he borrowed a wing, engine nacelles, landing gear with a front strut and a number of other, smaller units and assemblies. The fuselage was completely new, narrower than that of the original, with a glazed nose and an extensive bomb bay, as well as a two-keel spaced tail unit.

The all-metal G5N mid-wing was borrowed from the American Douglas DC-4E transport aircraft that served as the prototype. It had an unprecedentedly large span for Japanese cars - more than 42 m.Four new Nakajima NK7A Mamoru 11 radial engines with a capacity of 1870 hp were used as power plants. from.

The G5N's all-metal fuselage was designed from scratch by the Japanese. The aircraft was the first in Japan with a front landing gear.

Defensive armament included two 20-mm Type 99 Model 1 cannons (one each in the dorsal and tail turrets) and four 7.7-mm Type 97 machine guns for the bow, lower and two side rifle mounts.The maximum bomb load was supposed to reach 4000 kg (when flying over long distances - 2000 kg). The crew consisted of seven people.

The flight test results did not meet the customer's expectations. Fully equipped and armed, the Shinzan turned out to be almost 20% heavier than planned, its engines were unreliable, and its characteristics - primarily speed and range - were unsatisfactory. Despite this, three more experimental G5N1s and two modified G5N2s were built with the proven, but even less powerful (1530 hp) Mitsubishi Kasei 12 engines. The lack of power was too obvious, and in the end Kaigun Koku Hombu abandoned plans for further development of the aircraft as a bomber. Two experimental G5N1s were also equipped with Kasei 12 engines and, together with two G5N2s, converted into a transport version, designated "Shinzan KAI Model 12 Transport Aircraft" (G5N2-L Model 12). The firing points were dismantled and the bomb bay was converted into a cargo bay. The crew was reduced to six people.

The G5N2-L aircraft were used as transport aircraft almost until the end of the war. They flew on the routes connecting the Japanese Islands with Hong Kong, Taiwan, the Philippines, about. Tinian and the Mariana Islands. At the turn of 1944-1945, two vehicles were lost.

Despite the fact that the G5N project was unsuccessful, the company "Nakajima" acquired extremely important experience, which was later used in the development of the next four-engined bomber G8N "Renzan".

Heavy Bomber First flight: 1943 Nakajima

G8N Renzan (Mountain Range) . The failure with the G5N Shinzan forced Kaigun Koku Hombu to return to the twin-engine bomber concept for a while. However, by the end of 1943, after analyzing preliminary designs and design parameters, it became clear to both the developers and the customer that the twin-engine aircraft was not able to meet the requirements. This conclusion was predictable, therefore, back in February 1943, Kaigun Koku Hombu handed over to the Nakajima company the preliminary design requirements of the 18-Si for a four-engine long-range bomber. To this, the fleet command was also prompted by reports from the fronts about the high efficiency of the American four-engine B-17 and B-24 bombers. In the final form, the assignment for the development of a new bomber, designated G8N1 "Renzan" (Mountain Range), was issued on September 14, 1943. It provided for the creation of a powerful defensive weapon and a well-protected vehicle that would develop a maximum speed of 592 km / h, climb 8000 m in 20 minutes and had a flight range of 3700 km with a full bomb load (4000 kg) and 7400 km without a load.

On October 23, 1944, the first flight was made by the prototype G8N1, which was an all-metal monoplane, the design of which was simplified as much as possible to facilitate mass production, with a mid-wing, having a laminar profile and high elongation with a relatively small surface area. It was equipped with four turbocharged (Hitachi Type 92) Nakajima Homare 24 radial engines with 2000 hp. everyone.

The all-metal mid-wing G8N had a laminar profile and was characterized by a fairly small surface area (112 m²; compared to 202 m² for the G5M) with a high aspect ratio. Inside it housed sealed fuel tanks with a total capacity of 13,450 liters. The main landing gear was retracted into the engine nacelles. The morally obsolete tail unit with end washers was replaced by a single keel tail.

An unprecedentedly powerful defensive armament for Japanese aircraft was represented by six 20-mm Type 99 Model 2 cannons (in the dorsal and ventral turrets, as well as in the tail mount) and four 13-mm Type 2 machine guns (twin in the mechanized bow turret and one in the windows on the sides of the fuselage).

In case of successful completion of the tests, it was planned to release 48 production G8N1 bombers by September 1945, including 16 experimental and pre-production vehicles. But in practice, it all boiled down to the construction of three more prototypes, which were completed in October 1944, March and June 1945. This delay was caused by the constant raids of American aircraft and the shortage of light alloys. In addition, the sharply deteriorating strategic situation in Japan forced to change priorities. Now there was no time for strategic bombers and the serial production of the Renzans had to be abandoned.

After the war, the fourth prototype of the G8N1 "Renzan" was transported to the United States, where it was thoroughly tested. The results surprised the Americans. The characteristics demonstrated by the Japanese bomber were much higher than those of the American "classmates" Boeing B-17 and Consolidated B-24 and were only slightly inferior to those of the Boeing B-29 strategic bomber. After the end of hostilities, the allies assigned the codename "Rita" to G8N1.

Photo	Description
	Drawing G5N2
	Drawing G8N1, (turbocharger at the bottom of the engine)
	G5N Shinzan at the Japanese airbase Atsugi, 1945
	G5N Shinzan. Cockpit and tail gunner.
	G8N Renzan in the USA, 1945

Throughout the war, the Japanese aircraft industry failed to mass-produce heavy strategic bombers capable of carrying a significant bomb load over long distances. Designed for naval aviation by Nakajima, two types of heavy four-engine bombers, the G5N Shinzan (Allied code name Liz) and the G8N Renzan (Allied code name Rita) never lived up to their expectations. The first of them was ready in April 1941, but did not go into production due to low flight characteristics. The second, much more advanced, could have been a very unpleasant surprise for the Allies if its creation had not been delayed, and the Japanese aviation industry was able to build this aircraft in significant quantities. However, neither of these happened. Naval aviation remained until the end of the war without strategic bombers.

Attempts by army aviation to acquire a heavy strategic bomber were even weaker. However, they were, and this fact should not be ignored.

In May 1943, Kawasaki was given the task of developing a project for a long-range four-engine strategic bomber for the Army's long-range bomber aviation. The assignment specified the basic requirements for the aircraft: a range of at least 4,500 km, a bomb load of at least 4,000 kg, and a pressurized cabin. Since Kawasaki was closely engaged in the production of the main fighter for the army, the Ki-61, the company was unable to allocate any significant capacity for the implementation of this project. The army leadership still did not seriously appreciate the importance of strategic aviation, and therefore, the project received the lowest priority level, and the serial construction of the aircraft was planned in the long term. Despite this, the Kawasaki designers developed a bomber project, which was approved by the army aviation command. Kawasaki not only started building a prototype aircraft, but also began to prepare technological equipment for serial production of the bomber.

As well as the appearance of large numbers of G8N in the fleet, the appearance of the Ki-91 could come as an unpleasant surprise for the allies. However, this did not happen. In February 1945, during one of the regular raids by American aviation, the technological equipment was completely destroyed and the prototype was destroyed, which by that time was at the final stage of construction. The armament of the aircraft was to be very impressive. The prototype has already managed to install cannon turrets controlled by electric motors in the bow, in the upper part of the fuselage and in the rear sections along two sides. The armament of one turret consisted of two 20 mm guns. Also, according to the project, it was planned to install a turret armed with four 20-mm cannons in the tail section of the prototype. At that time, not a single bomber in the world had such powerful defensive weapons! However, the plans were not destined to come true. After the destruction of a significant part of the expensive equipment along with the prototype, the Kawasaki management was simply unable to restore the program, and work on it was completely stopped. History played a cruel joke with the Ki-91 - its prototype was destroyed by the "super-fortresses" of the B-29. So ingloriously ended the career of the first strategic bomber of the Japanese army aviation that had not begun.

Photo	Description
	Drawing Ki.91

In 1944-1945. for the Japanese, American air raids became a real natural disaster. The USAF assembled not even dozens, hundreds of aircraft into one strike group. The consequences of the bombing were simply catastrophic, although the Japanese fought with exceptional courage, sometimes inflicting sensitive B-17 and B-24 squadrons, the situation changed for the worse with the start of the massive use of long-range B-29 bombers, which, without a bomb load, could escape at speeds from most Japanese interceptors. However, one should not think that the Japanese Air Force did not want to have such aircraft in service. Rather, on the contrary, if you recall, it was the JIAF that was one of the first to switch to the operation of heavy long-range monoplane bombers, having bought a license in Germany for the production of the Junkers G.38 aircraft. Its bomber version was produced at Mitsubishi factories under the designation Ki-20, and until 1940 formed the basis of long-range army aviation.

By the beginning of the Japanese aggression against the US and its allies, the Ki-20 had already been put into reserve. To replace it, several promising projects were being prepared, which, in terms of their design characteristics, were not inferior to the American B-17B. The undisputed leader in this direction was Nakadjima. In April 1941, tests began on the G5N1 "Shinzan" bomber, built on the basis of the multi-purpose American Douglas DC-4E aircraft. As it turned out later, the alteration did not benefit the DC-4. The Japanese aircraft was not very suitable for combat use, and all its prototypes were left for rear use. Two years later, a more powerful aircraft was built - G8N1 "Renzan" - this time the Japanese only used the experience of the Americans in the construction of heavy aircraft.

A little earlier, Nakadjima engineers, with the participation of officers from the Fleet Air Arm, began designing a new aircraft being developed as part of the "Z program". As conceived by the creators, the bomber was to be equipped with six Nakadjima Ha-54-01 (5000 hp) engines, carry powerful defensive weapons and a bomb load of about 20 tons. The geometric dimensions of the aircraft were amazing - 40-44 meters in length and 65-72 meters in wingspan. Takeoff weight was estimated at 125-160 tons.

Naval aviation is very interested in this aircraft. In the middle of 1943, the leadership of the Navy issued official requirements for a machine of this class, adjusting the ceiling to 15,000 meters. The Nakadjima project also received a new designation - the Marine Experimental Heavy Bomber "Fugaku", to which the purely naval G10N1 was later added. Looking ahead, let's say that the Na-54-01 engines were still at the design stage and could actually be prepared for serial production closer to 1946. The prototype itself, according to preliminary estimates, could be fully completed by the winter of 1945.

The construction of huge slipways and structural elements of the bomber, which had been vigorously begun, was abruptly stopped in the spring of 1944. The leadership of the Air Force urgently needed production facilities for the construction of fighters, due to which the "Z program" was closed. Approximately the same picture was observed in Germany, where during 1944-1945. dozens of jet bomber projects were rejected, some of which were at the stage of making working drawings. The Germans, however, realized it in the spring of 1945, deploying the construction of several prototypes of different companies at once, but time was hopelessly lost and not one of the aircraft was even half ready.

The Japanese did the same, dismantling the stocks and sending the finished G10N1 units for scrap. The fallacy of this decision became apparent in the summer of 1945, when the Americans occupied part of the Japanese islands near the mother country. Here, the G10N1s could come in handy with their huge bomb load and large ceiling, one squadron of which could easily raze any enemy base to the ground.

Bibliography

• "Encyclopedia of military engineering " /Aerospace Publising/
• "Japan Warplanes of World War II" /Oleg Doroshkevich/

August 05, 2018
The G5N, which was never put into service, nevertheless received a codename from the allies - "Liz", a feminine name assigned only to bombers. The transport use of prototypes of a heavy bomber is a payback for the low flight characteristics of the aircraft.

April 27, 2018

G8N Renzan is a heavy four-engined bomber that never became a saving super-fortress for the Imperial Japan.
High performance characteristics "Renzan" owes, first of all, to its "laminar" wing with a small area and a power plant with a capacity of 8000 hp.

April 28, 2018

It is interesting to compare with the attempt of the Germans to create their own strategic bomber Me 264 , also an unfulfilled program due to the Allied bombing and end of the war.