Mitsubishi G1M1

The Mitsubishi G1M1 was a designation given retrospectively to the sole Mitsubishi Ka.9, the first prototype in the series of aircraft that would enter service as the G3M ‘Nell’. The Japanese Navy’s first attempt to produce a modern long range bomber had been part of the ambitious Experimental 7-Shi Programme of 1932. It had been hoped that this programme would produce a new generation of Japanese naval aircraft, but the only successful aircraft to emerge from it was the Kawanishi E7K ‘Alf’ Navy Type 94 Reconnaissance Seaplane. The only land based bomber to emerge from the programme was the Hiro G2H, which had made its maiden flight early in 1933. The G2H had the range required, but lacked the speed, and only eight would be built, eventually entering service as the Type 95 Heavy Land-Based Attack aircraft of 1935.

In 1933 the head of technical developments at the Naval Aircraft Establishment was Rear Admiral Isoroku Yamamoto. He was convinced that the navy needed a long range land based bomber, to be used as a defensive weapon from bases on the scattered islands of Japan’s Pacific empire. The G2H was clearly not going to be that aircraft, and so early in 1933 Yamamoto gave Mitsubishi a non-competitive contract to produce a long range high speed multi-engined monoplane. No bomb load or performance figures were specified, giving Mitsubishi free reign.

Mitsubishi was chosen because in the late 1920s it had developed strong relationship with Junkers. In 1928 Mitsubishi had purchased licenses to a number of Junkers patents and to a series of their aircraft designs, and by the start of 1933 had designed the Ki-1, Ki-2 and Ki-20 bombers for the Japanese Army Air Force. A number of Mitsubishi engineers, amongst them Sueo Honjo, had also received design training from Junkers.

Sueo Honjo became the chief engineer on Navy Project 435, or the Experimental 8-Shi special reconnaissance plane. The new aircraft was given the Mitsubishi designation Ka.9.

The Ka.9 emerged on 18 April 1935. It was a twin engined monoplane, powered by two 650hp Hiro Type 91 engines. It had a slim streamlined fuselage, twin vertical fins and rudders, and Junkers double wings. In this design a second much smaller airfoil was mounted on the back on the main wing. The gap between the two wings increased lift, especially when the aircraft was flying at a steep angle (either when climbing or landing), but at the expense of added drag. It was also the first Japanese military aircraft to have a retractable undercarriage.

Yamamoto was amongst the first people to test the aircraft, and was immediately impressed with its performance. Honjo had produced an aircraft with a range of 3,265 nautical miles, better than any contemporary military aircraft. The Ka.9 was given the short description designation G1M1, making it the first entry in a new land-based bomber sequence (the eight Hiro G2H bombers did not enter service until the following year).

Mitsubishi were rewarded with Navy Project 79, for the Navy Experimental 9-Shi land-based attack plane. This would emerge as the Ka.15, and would enter service as the G3M ‘Nell’.

The sole G1M1 was used as an experimental airframe, and was used to test Mitsubishi’s 14-cylinder Shinten twin-row air cooled radial engines. These engines produced 920hp, but only increased the aircraft’s speed by 15mph, and were very unreliable.

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How to cite this article: Rickard, J (4 December 2008), Mitsubishi G1M1 ,

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