Empire of Japan (1941)
Strategic Bomber- 1 Scale Mockup Built

The Mitsubishi G7M “Taizan” (泰山/Great Mountain) was a planned long range strategic bomber for Imperial Japan’s Army Air Service. Developed out of the need for a bomber capable of striking the continental United States, the Taizan would face a series of developmental problems, ultimately leading to the cancellation of the project.

History

Prior to the start of World War II, Japan had foreseen that in a potential future conflict with the United States, it would require a long range bomber capable of striking the US mainland. In order to fulfill this requirement, a review was conducted in 1941 of all the Imperial Japanese Navy’s bomber aircraft in service. It was revealed that the entirety of the Japanese bomber arsenal was incapable of striking targets in the United States from the Japanese airfields. The Mitsubishi G4M “Betty” was one of Japan’s newest aircraft being pushed into service. Despite its superior range of 3,749 mi (6,043 km) compared to previous IJN bombers, it still was not sufficient enough to strike the US mainland or targets deep in the Soviet Union. As a result of this, the Naval Kōkū Hombu (Aviation Bureau) issued the 16-shi specification in 1941 for a long range bomber. The 16-shi specification would call for a bomber capable of flying at least 361 mph (580 km/h) with a maximum range of 4,598 mi (7,340 km).

Interested in this specification, Mitsubishi’s staff began work on a design that would meet the criteria set by the Kōkū Hombu. Mitsubishi engineer Kiro Honjo (the designer of the G3M and G4M) proposed a four engine design, but this was promptly rejected by the Kōkū Hombu. As a result, another Mitsubishi engineer by the name of Kijiro Takahashi submitted his own design. Upon inspection by the Kōkū Hombu, Honjo’s design was approved and given the green light to proceed. Within Mitsubishi, the 16-shi design was known as the “M-60”. Takahashi’s design was to be powered by two “Nu” engines. The Nu was a 24 cylinder liquid cooled engine which was able to provide 2,200 hp at 16,404 ft (5,000 m) but, due to the start of Operation Barbarossa, Germany was unable to export machinery and tools needed to manufacture the Nu engine. Unfortunately for Takahashi, this turn of events would prevent his design from being completed. As a result of this, Takahashi fell out with the Kōkū Hombu and Kiro Honjo would take over the M-60 project. This time, Honjo followed the Kōkū Hombu’s suggestion and used two engines instead of his idea of four. Under Honjo’s lead, the Taizan’s power plant was changed to two 18 cylinder Mitsubishi Ha-42-11 engines capable of generating 2,000 hp each. It was also seen that Honjo’s design was less aerodynamic than Takahashi’s due to the weaker engines and heavier armament.

On October 31st of 1942, an evaluation was conducted on the work done so far, and a performance estimation gave the Taizan a range of 3,454 mi (5,559 km) and a speed of 332 mph (518 km/h) at 16,404 mi (5,000 m). Falling short of the original 16-shi specification, Mitsubishi scrambled to make adjustments but further revised estimates stated that the design didn’t see any improvements, and actually saw some deterioration. By the time the Taizan’s design was completed in late 1942 and ready for construction of a wooden mockup, a new 17-shi specification was released calling for a new bomber design. Kawanishi took up the design and created the K-100 bomber project. Seeing promise and a better alternative to the Taizan, the Kōkū Hombu ordered all work on the Taizan to be halted until the K-100 could be completed and evaluated. Kawanishi completed initial work on the K-100 and a comparison was made between K-100 and Taizan in the summer of 1943. The Taizan’s range differed significantly from the proposed normal range from 2,302 mi (3,705 km) to 1,726 mi (2,778 km). Due to the significant range reduction, the Kōkū Hombu stopped supporting the Taizan. With no more interest and reason to develop the Taizan, Mitsubishi would finally shelve the project and stop all work on it.

Design

From an exterior aesthetic point of view, the Taizan bears a striking resemblance to the German Heinkel He 177. The nose of the Taizan was rounded and glazed over, a new design not in use by any Japanese bombers at the time. The wings of the Taizan were mounted mid fuselage, and were to be constructed out of metal. Fabrics, however, were to be used for the cover of the Taizan’s ailerons and rudder.

Ordinance wise, the Taizan was to carry a maximum bomb load of 1,764 lbs (800 kg). The defensive armament underwent several changes. Takahashi’s Taizan design was to be armed with two 20mm Type 99 Mk.2 cannons and two 7.7mm Type 97 machine guns. Honjo’s initial design would carry two 20mm Type 99 Mk.2 cannons, two 13mm Type 2 machine guns and two 7.92mm Type 1 machine guns. Later on, the armament finalized at two 20mm Type 99 Mk.2 cannons and six 13mm Type 2 machine guns. There would have been one Type 99 Mk.2 in the nose and one in the tail. There would have been two Type 2 machine guns in the forward upper fuselage turret, two in the rear fuselage turret and two in ventral position, firing rearwards.

Operators

• Empire of Japan – The Taizan would have been operated by the Imperial Japanese Navy Air Service.

Gallery

Sources

Dyer, E. M. (2013). Japanese secret projects: experimental aircraft of the IJA and IJN 1939-1945. Burgess Hill: Classic., Aircrafts of Imperial Japanese Navy. (n.d.). Retrieved February 06, 2018, from http://zenibo-no-milimania.world.coocan.jp/epljn.html, Images: Side Profile Views by Ed Jackson – Artbyedo.com